Materials Science & Engineering R 161 (2024) 100834
Contents lists available at ScienceDirect
Materials Science & Engineering R
journal homepage: www.elsevier.com/locate/mser
Recent progress in high-entropy alloys for laser powder bed fusion: Design,
processing, microstructure, and performance
Asker Jarlöv a,b, Zhiguang Zhu c , Weiming Ji a , Shubo Gao a , Zhiheng Hu b,
Priyanka Vivegananthan a , Yujia Tian a , Devesh Raju Kripalani a , Haiyang Fan a,d, Hang Li Seet b,
Changjun Han e, Liming Tan f , Feng Liu f, Mui Ling Sharon Nai b,* , Kun Zhou a,*
a
School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Republic of Singapore
Additive Manufacturing Division, Singapore Institute of Manufacturing Technology (SIMTech), Agency for Science, Technology and Research (A*STAR), 5 Cleantech
Loop, Singapore 636732, Republic of Singapore
c
School of Mechanical Engineering, Nanjing University of Science and Technology, Nanjing 210094, China
d
Yantai Research Institute, Harbin Engineering University, Yantai 264006, China
e
School of Mechanical and Automotive Engineering, South China University of Technology, Guangzhou 510640, China
f
State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
High-entropy alloys
Laser powder bed fusion
Alloy design
Computational modeling
Performance
Laser powder bed fusion (LPBF), as the most commercialized metal additive manufacturing technique, is
tantalizing the metallurgical community owing to its capabilities of directly producing highly intricate parts with
complex geometries and achieving superior properties compared to those of conventionally manufactured alloys.
High-entropy alloys (HEAs) represent a class of novel materials consisting of multiple principal elements in nearequiatomic ratios, revolutionizing the alloy design concept. LPBF has been employed to fabricate HEAs in
numerous attempts to improve their outstanding mechanical, physical, and chemical properties. This review
systematically compares seven unique classes of LPBF-produced HEAs—the 3d transition metal HEAs, eutectic
HEAs, precipitation-strengthened HEAs, refractory HEAs, metastable HEAs, interstitial HEAs, and high-entropy
matrix composites—pertaining to their feedstock preparation, printability, microstructure, strengthening
mechanisms, material properties, and potential applications. Additionally, the computational modeling of HEAs
for LPBF is extensively discussed. This work aims to guide relevant research in the field by systematically
reviewing the advancements in the design strategies employed for the successful fabrication of HEAs by LPBF.
1. Introduction
Conventional alloys consist of minor elements added to a principal
element to tune its properties, with typical examples including steels
[1], titanium alloys [2], aluminum alloys [3], and nickel-based super­
alloys [4]. In stark contrast to the conventional approach, high-entropy
alloys (HEAs) incorporate multiple principal elements in
near-equiatomic ratios [5,6], allowing them to span a previously un­
charted compositional space. These multicomponent alloys have capti­
vated the research community because of their outstanding mechanical,
physical, and chemical properties, which include enhanced
strength–ductility synergy [7,8], high corrosion and irradiation resis­
tance [9,10], remarkable fracture resistance at cryogenic temperatures
[11], and a low transition temperature for superconductivity [12]. These
outstanding properties are attributed to four core effects intrinsic to the
complex composition, i.e., the high-entropy, lattice distortion,
sluggish-diffusion, and cocktail effects [13,14].
However, the multi-element nature of HEAs complicates their
fabrication because of potential elemental segregation and the forma­
tion of undesired intermetallic phases. Moreover, mixing multiple ele­
ments in a near-equiatomic ratio tends to increase the cost of producing
HEAs and compromise their recyclability [15,16], meaning they should
target high-value applications where their outstanding properties are
required. Therefore, a fabrication technique that enables the exploration
of a wide composition range, minimizes elemental segregation, and is
suitable for low-volume production of specialized high-value parts
would be ideal.
In recent years, additive manufacturing (AM), also known as three-
* Corresponding authors.
E-mail addresses: mlnai@simtech.a-star.edu.sg (M.L.S. Nai), kzhou@ntu.edu.sg (K. Zhou).
https://doi.org/10.1016/j.mser.2024.100834
Received 6 December 2023; Received in revised form 11 July 2024; Accepted 6 August 2024
Available online 9 September 2024
0927-796X/© 2024 Published by Elsevier B.V.
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
dimensional (3D) printing, has transitioned from being solely used for
prototyping to a renowned technique for fabricating metallic parts [14].
Particularly, laser powder bed fusion (LPBF) offers several advantages
over conventional manufacturing, including unrivalled design freedom,
reduced material waste, and unique microstructure control to achieve
the desired material properties [17–19]. As a processing technique for
HEAs, LPBF provides several specific advantages, such as a rapid so­
lidification rate to suppress the formation of harmful intermetallic
phases and elemental segregation [14], the possibility of
high-throughput screening through mechanical alloying [20], remark­
able geometrical accuracy that results in unmatched design freedom
[21], and an economical path to achieve low-volume production of
highly specialized parts [17].
Despite the tremendous advantages of LPBF, the limited portfolio of
alloys that can be processed by this technique remains a major obstacle
[20]. The complex thermal history with cooling rates on the scale of
105–108 K s–1 [21] tends to introduce processing defects, including so­
lidification cracks, keyhole and lack-of-fusion pores, and warping,
which can severely degrade the performance of the printed part [22,23].
To address this issue, new alloys designed explicitly for the LPBF process
are needed, along with optimization of their printing parameters and
post-process treatment. The enormous number of alloys offered by the
HEA concept has already yielded promising candidates for LPBF,
demonstrating how intelligent alloy design can circumvent common
processing defects [23-25].
To effectively identify novel alloys and potential knowledge gaps, a
structured approach is needed to categorize the alloys into different
classes based on their design strategy. Fig. 1 illustrates how LPBFfabricated HEAs can be grouped based on their underlying design
strategy. With the addition of extrinsic reinforcing particles or nonmetallic elements, high-entropy matrix composites or interstitial
HEAs, respectively, can be fabricated. If the HEA is designed to yield a
dual-phased eutectic microstructure, it can be categorized as a eutectic
HEA. If the as-printed HEA is designed to have a metastable micro­
structure, the HEA can be classified as a metastable HEA. Refractory
HEAs mainly consist of refractory elements, while precipitationstrengthened HEAs are designed to form precipitates of secondary
phases to enhance their mechanical performance, mainly by adding Ti
and Al. Finally, 3d transition metal HEAs mainly consist of 3d transition
elements.
Fig. 1. Systematic categorization of HEAs for LPBF based on their design strategies [13,22,23,26,27–42].
2
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
properties as well as the strengthening mechanisms active in each class,
is presented. The article then analyzes the potential industrial applica­
tions of LPBF-fabricated HEAs before concluding with an outlook on
current knowledge gaps and future research trends.
While the enhanced freedom in compositional design allows for
developing novel high-performance alloys for LPBF, tremendous chal­
lenges are also introduced as conventional trial-and-error experiments
are unfeasible in terms of the required time and monetary cost. There­
fore, computational simulations are necessary to guide alloy design and
reduce the number of expensive experiments [43–45]. Additionally,
computational modeling may be used to describe the multi-physics
mechanisms occurring during the LPBF process, including energy ab­
sorption, melt flow, elemental segregation, crack formation, and part
solidification, and speed up the process optimization. Various ap­
proaches have been adopted to understand and optimize the LPBF
process, including machine learning algorithms [46], calculation of
phase diagrams (CALPHAD) [24,47], the finite-element method (FEM)
[23,48], computational fluid dynamics (CFD) [49], molecular dynamics
simulations [50,51], and other numerical methods [52–54]. A complete
understanding of the available computational tools is required to ensure
further progress and industrial adoption of LPBF-fabricated HEAs.
Although several review papers have focused on the LPBF of HEAs
[14,55–62], including some that focus on the individual classes of HEAs
[63–66], no previous work has systematically compared the different
classes in terms of their printability, microstructure, material properties,
and potential applications. Drawing on recent advancements in the field,
this review conducts a thorough examination of the seven unique classes
of LPBF-fabricated HEAs. We distinguish these classes in terms of feed­
stock preparation, printability, microstructure, material properties, and
potential applications in the energy, aerospace, and biomedical sectors.
Since a comprehensive review covering the computational modeling of
HEAs for LPBF is still absent in the current literature, this review also
provides an in-depth discussion of the modeling and simulation tech­
niques employed in designing HEAs for LPBF, including CALPHAD,
FEM, CFD, molecular dynamics simulations, and ab initio calculations.
The role of these techniques in compositional and process design is
systematically discussed to provide a holistic overview.
The subsequent section reviews the modeling techniques employed
to facilitate the adoption of LPBF-fabricated HEAs. Then, the feedstock
preparation and LPBF process are introduced, and the typical processing
parameters employed for the different classes of HEAs are discussed. A
comparison of the individual classes is provided, followed by an indepth review of the microstructures formed for different alloys of each
class. Next, a discussion on the mechanical, physical, and chemical
2. Compositional design and modeling of HEAs for LPBF
This section introduces the computational simulation methods
employed to accelerate the adoption and deepen the understanding of
LPBF-fabricated HEAs, with a focus on compositional and process
design. Existing methods that can be extended to the HEA concept are
also reviewed.
To perfectly model reality in all its complexity is a near impossible
task, and the different simulation techniques must employ approxima­
tions to reduce the computational cost. A crucial step in modeling the
LPBF of HEAs thus lies in picking the best-suited technique, where the
imposed approximations do not significantly compromise the accuracy.
This decision requires a deep understanding of each simulation tech­
nique and its underlying theoretical framework. Numerous computa­
tional tools have been used to describe the LPBF process, and their
respective roles are highlighted in Fig. 2. As the specifics of each tech­
nique are beyond the scope of this review, only a brief introduction for
each technique is provided before discussing their use in modeling the
LPBF of HEAs.
At the nanoscale, ab initio calculations and molecular dynamics
simulations can provide atomistic insights into the printed parts. Ab
initio calculation is a quantum mechanical simulation technique in
which the electrons are treated as wave functions [73,74]. Utilizing
several approximations, the Schrödinger equation can be solved, and in
principle, any material property can be estimated with high accuracy.
Molecular dynamics simulation is a non-quantum mechanical method
where highly accurate force fields are used to describe the interaction
between atoms [75]. This approach to estimate the interatomic forces
avoids the need to solve the Schrödinger equation, thus allowing for
simulations on a larger temporal and spatial scale than ab initio
calculations.
CALPHAD is a commonly employed method that predicts the phase
composition (i.e., the type and amount of each phase present) of a spe­
cific alloy [76,77]. By combining experimental databases with ab initio
calculations, CALPHAD can reduce the reliance on time-consuming
Fig. 2. Role of different simulation techniques in modeling the LPBF of HEAs. Images are taken and modified from refs. [67–72].
3
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
experiments by making thermodynamic predictions readily available for
multiple alloy systems. CFD predicts the temperature fields and viscosity
of the melt pool while treating the solid parts as the boundary condition
[78]. The FEM sections the structure into a fine mesh to not only predict
the temperature fields but also residual stress in the as-printed part [79].
Machine learning is an informatics-based method where a computer
algorithm is trained on a dataset to predict the outcome of situations
outside the dataset [80]. The algorithm can be used for multiple pur­
poses, including accelerating the screening process of HEAs for LPBF,
optimizing the LPBF process parameters, and predicting the mechanical
and functional properties for targeted applications, provided that a
sufficiently large dataset exists. This dataset could come from experi­
ments, one of the above simulation methods, or a mixture of both.
In addition to the techniques shown in Fig. 2, several numerical
models, i.e., where a numerical time-stepping algorithm captures the
behavior of the LPBF process over time, have been developed. These
models are capable of predicting the melt pool dimension [81], relative
density [82–84], compositional heterogeneity in mechanically alloyed
powder [85], etc.
2.1. Compositional design
Numerous tools have been introduced to accelerate the screening for
promising alloys. In addition to outstanding material properties, print­
ability must be considered when designing alloys for LPBF. The tools
used for the compositional design of HEAs include CALPHAD, atomistic
simulations, and machine learning.
CALPHAD is able to assist in designing HEAs for LPBF, although the
high cooling rates result in non-equilibrium conditions, unlike pre­
dictions by the phase diagrams. Commonly employed criteria to ensure
good printability include a narrow solidification range of less than 100
◦
C and secondary phases having a solvus temperature of more than 125
◦
C below the solidus temperature [27,86]. Both criteria are adopted
from the welding literature as LPBF can be seen as an iterative welding
process [87,88]. The first criterion is used to limit solidification cracking
by reducing the time that the alloy remains in the critical solidification
range (~95–99% solidified). The second criterion is adopted to suppress
strain–age cracking caused by the sudden strengthening from pre­
cipitates formed quickly after solidification, thereby preventing the
relaxation of thermal stress. These criteria were used to design a
high-entropy matrix composite with excellent printability by performing
~107 equilibrium calculations (Fig. 3a).
The more conventional use of CALPHAD, namely to predict the phase
stability of an alloy, has also been leveraged to design HEAs, including
metastable [36,89] and eutectic [90,91] HEAs. Phase diagrams have
been extensively used to identify alloys with an eutectic point, often in
combination with machine learning to traverse the large compositional
space [92]. To account for slow growth kinetics during the
non-equilibrium LPBF process, a composition that is skewed towards the
slower-growing phase can be utilized to obtain an eutectic lamellar
microstructure. For example, when designing an FCC–Laves eutectic
HEA for LPBF, the Al content was intentionally set to exhibit
hyper-eutectic composition to promote the growth of the Laves phase
because of its slower growth kinetics during rapid solidification [93].
The use of non-equilibrium Scheil–Gulliver simulations provides
information regarding the precipitation of different phases and crack
susceptibility during solidification [24,26,86]. By calculating the vol­
ume fraction change as a function of temperature within the critical
solidification range, the solidification crack index can be calculated to
allow for quantitative comparison between different alloys (Fig. 3b)
[86]. This index serves as an easily accessible metric to evaluate the
crack susceptibility and should be included in datasets for machine
learning algorithms.
Numerous additional design criteria have been proposed based on
Scheil–Gulliver solidification simulation and leveraged to optimize the
printability of conventional alloys. These criteria allow for evaluating
Fig. 3. Use of CALPHAD to design LPBF-fabricated HEAs: (a) Predicted phase
fraction diagram of (CrCoNi)96.9W0.95Al0.65Nb0.47Re0.47Ti0.30C0.24 [27]. (b)
Average solidification cracking index (SCI) in the critical solidification range of
Ni46.23Co23Cr10Fe5Al8.5Ti4W2Mo1C0.15B0.1Zr0.02 (MNiHEA) and other commer­
cial precipitation-strengthened Ni-based superalloys [86].
the tendency to form hot cracks (through the use of Clyne and Davis
[94], Kou [95], or Tang [96] criteria), dendritic grains (through the
Kurz–Giovanola–Trivedi model [97]), pores (through Buckingham’s
Π-theorem [98]), etc. Consolidating the above criteria into a computa­
tional framework would provide a holistic view of the effect of chemical
composition on the freezing range, the tendency to form columnar
grains, and susceptibility to processing defects such as hot cracks,
lack-of-fusion pores, keyhole pores, and balling [99]. Extending such a
design concept to the high-entropy space can drastically accelerate the
design process of printable HEAs.
Ab initio calculations are capable of obtaining the thermal conduc­
tivity, melting point, cohesive energy, elastic constants, density of states,
and ground-state energy [100–102]. Such calculations have been used to
identify suitable alloys for LPBF from the Al–Ti–V–Fe–Co–Ni–Zr–Sm
[44,103] and Cr–Co–Ni [27] alloy systems. Depending on the specific
application of the designed alloy, different properties must be opti­
mized. For alloys designed to be used at elevated temperatures,
high-temperature creep will be one of the major challenges, and the
atomic diffusion must be accurately estimated [104]. As the ab initio
approach can be used to obtain the parameters of adhesion and atomic
diffusion between extrinsic particles and the matrix phase, it is suitable
for designing high-entropy matrix composites for such applications
[105]. For HEAs intended for structural applications, the shear modulus
and Poisson’s ratio are essential. The ability to theoretically calculate
any material property using the ab initio method makes it advantageous
over other simulation techniques, although the high computational cost
restricts the number of computations that can be performed. As
LPBF-fabricated HEAs start to target functional applications, the use of
4
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
ab initio calculations to calculate the magnetic and catalytic properties
will become increasingly important [106,107].
Another potential use of atomistic simulations is to predict the
microhardness, stress required for homogenous dislocation nucleation,
twinability, and stacking fault energy, i.e., the energy penalty for dis­
rupting the stacking sequence [108,109]. Reduced stacking fault energy
can improve printability by enabling the thermal stress induced during
the printing process to be consumed by forming crystallographic defects
[23,110]. Molecular dynamics simulations have demonstrated the
ability to calculate the stacking fault energy over a sizeable composi­
tional space [109,111]. The interatomic force field allows molecular
dynamics simulations to obtain these properties using a much larger
simulation cell than ab initio calculations, thereby giving nanoscale in­
sights into these deformation mechanisms [74]. However, the reliance
on accurate force fields limits molecular dynamics simulations to
comprehensively studied alloy systems, thus restricting the exploration
of novel alloy chemistry to ab initio calculations. With the emergence of
new force fields describing a more comprehensive composition range,
molecular dynamics simulations are expected to see increasing usage as
a computationally more efficient alternative to ab initio calculations.
Machine learning is emerging as a promising approach to uncover
hidden correlations in the large body of available literature [112–114].
However, regarding the compositional design of HEAs for LPBF, print­
ability must be considered as an additional constraint. The high cost of
producing high-quality powder limits the currently available data on
LPBF-fabricated HEAs, thus restricting the prospect of leveraging ma­
chine learning as large datasets are required to train the algorithm.
Obtaining such databases from computational algorithms is a promising
alternative to facilitate the use of machine learning. Input parameters to
consider include the alloy’s freezing temperature range, liquid viscosity,
thermal expansion, and shear-to-bulk modulus ratio [115]. Neural net­
works, natural language processing, and physics-informed artificial in­
telligence are different types of algorithms that have demonstrated high
potential in providing user-friendly guidelines for the design of HEAs
[112–114]. However, it is essential that the available data are normal­
ized prior to the training process to ensure that all data points are
collected under similar conditions. As reliable databases become more
available, machine learning is expected to see increasing application due
to its immense potential to accelerate material discovery.
2.2. Process design
Cr–Mn–Fe–Co–Ni HEAs are by far the most investigated alloy system
for LPBF, and thus, novel simulation methods tasked to model the
printing of HEAs typically focus on these alloys as a benchmark [46,81].
Machine learning has a high potential to optimize the printing process of
HEAs, with the main challenge being to identify input parameters that
predict the printability [46,115]. Alternatively, regression models could
be used to assess suitable printing parameters rapidly. These models
form a relationship between the relative density RD and different pro­
cessing parameters Yx according to
RD = a1 + a2 Y1 + a3 Y2 + a4 Y3 + a5 Y1 Y2 + a6 Y1 Y3 + a7 Y2 Y3 + a8 Y21
+ a9 Y22 + a10 Y 23 + …,
(1)
Fig. 4. Simulation techniques employed to model the LPBF process of HEAs: (a) Printability map for CrMnFeCoNi HEAs calculated using the FEM. LOF, KEY, BALL,
and G refer to lack of fusion and keyhole pore formation, balling, and good quality, respectively [48]. (b) Experimental validation corresponding to points 1–4 in (a).
(c) CFD simulations revealing the temperature distribution in the melt pool of CrFeCoNiMo0.2 [49]. (d) Simulated and calculated thermal gradients in the melt pool
of (c).
5
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
evaluate the microstructure, phase composition, and mechanical prop­
erties of printed parts. CFD simulations can analyze the temperature
distribution in the melt pool, revealing a lower temperature gradient at
the edge than at the center of the melt pool. The lower temperature
gradient generally allows for the precipitation of secondary phases
(Figs. 4c and d) [49]. Comprehensive information on such secondary
phases is required to understand the crack susceptibility of as-printed
HEAs as precipitates can inhibit crack formation during printing. Sec­
ondary phases with a larger molar volume than the matrix phase can
inhibit intergranular cracks by exerting compressive forces that prevent
crack formation [24] while secondary phases with a lower stacking fault
energy can mitigate the crack formation by consuming thermal stress
caused by the printing process through the formation of stacking faults
[23]. Leveraging CALPHAD and atomistic simulations to rapidly assess
the molar volume and stacking fault energy of different phases is
necessary to extend these strategies to other alloy systems.
The compositional heterogeneity of HEAs at the atomic level advo­
cates using atomistic simulations to gain insights into the solidification
process during LPBF. Recent success in using molecular dynamics sim­
ulations to model the LPBF process provides an avenue for gaining such
insights [122,123]. These studies have focused on printing using nano­
sized powder particles to combat the limited spatial scale of the simu­
lations and elucidated the effect of the scan speed, laser power, and scan
strategy on the atomic distribution and nanoscale mechanical response
[50]. The redistribution of elements in the melt pool, columnar growth,
geometry of the solidification front, and formation of vacancies and
stacking faults can be accurately captured and guide how to leverage
LPBF to architect the microstructure of HEAs on the nanoscale (Fig. 5)
[51].
To conclude, the selection of a suitable simulation method depends
on the type of property and the length scale of the study. Atomistic
simulations provide a promising avenue to understand the relationship
between the chemical composition and different material properties.
However, the limited temporal and spatial scale prevents the techniques
from providing insights into the printability of the designed alloys,
making them more suitable as complements in a computational frame­
work in conjunction with the FEM, CALPHAD, or CFD. Such a
where the coefficients ax are obtained by fitting experimental data. Both
quadratic and cubic forms of Eq. (1) have been used to optimize the
printing process of multiple HEAs [82–84].
Another common method to assess the printability of an alloy is by
obtaining the printability map of the specific alloy. The use of the FEM
allowed for the calculation of printability maps for equiatomic
CrMnFeCoNi, which are in good agreement with experiments (Figs. 4a
and b) [48]. Processing maps have also been generated for multicom­
ponent shape memory alloys by estimating the thermophysical proper­
ties using thermodynamic-simulation software and physics-based
Eagar–Tsai models [116,117]. Extending these simulations to HEAs
shows promise in optimizing the printing process.
The FEM can be used to obtain the thermal distribution during the
LPBF process and is thus adopted to mitigate printing defects caused by
large temperature differences within the same part. Particularly, re­
fractory HEAs are susceptible to warping and the formation of cracks. By
tuning the process parameters, the temperature distribution and thermal
stress can be homogenized, thereby eliminating these defects [118,119].
Mechanical alloying is a process that facilitates the screening of HEAs
using LPBF by circumventing the need for expensive gas-atomized
powder (Section 3.1), but additional insight into obtaining composi­
tionally homogenous alloys is still needed. An integrated discrete
element method (DEM)–FEM–CALPHAD framework has been used to
optimize the LPBF process parameters of a mechanically alloyed
Cr–Fe–Co–Ni HEA [85]. The DEM, FEM, and CALPHAD were tasked to
model the packing of the heterogeneous powder bed, temperature field
from multi-layer and multi-track laser melting, and diffusion kinetics in
the liquid and solid phases, respectively. Using the density and particle
radius of the powder, the optimal weight fraction of each powder, layer
thickness, molten time duration, and molten temperature were pre­
dicted for achieving the targeted chemical composition and elemental
homogeneity. To further model the use of mechanically alloyed powder,
recently developed physics-based models that predict the elemental
distribution of mixed powders in conventional alloys can be expanded to
HEAs [120,121].
Computational simulations and modeling have been further used to
Fig. 5. Molecular dynamics simulation of LPBF-fabricated HEAs. Atomic model for LPBF processing of CrFeNi (left). The simulation cell is highlighted in the red box,
and the atoms are colored according to their structure types (green: FCC; red: hexagonal close-packed (HCP); grey: unidentified). Cross-sectional view of the model at
different time (right). The atoms inside and outside the blue boxes are colored according to their temperature and structure types, respectively. The red arrows, red
arcs, and blue arrows show the direction of heat conduction, boundary of the columnar crystal, and depth of the molten pool, respectively [51].
6
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
framework would be computationally more efficient as the different
advantages of each technique can be fully utilized. For example, CAL­
PHAD can rapidly provide information regarding macro-scale properties
(e.g., phase composition, solidus–liquidus temperature range, and
elemental composition of different phases), while ab initio calculations
provide an opportunity to predict the material properties for previously
unexplored alloys. The individual simulation techniques can be used to
access a wide range of length scales, including macroscale (FEM),
mesoscale (CALPHAD and CFD), and nanoscale (ab initio and molecular
dynamics simulations).
The development of computational frameworks specifically for LPBF
of HEAs represents a promising path to accelerate their industrial
adoption, although continued progression is necessary to advance the
field further. Machine learning, in particular, has the potential to
accelerate the design of novel HEAs drastically. However, machine
learning requires a large quantity of data for accurate predictions.
Generating such databases using experiments negates the motivation for
using simulations in the first place, i.e., to mitigate the reliance on costly
and time-consuming experiments. Currently, in-house databases are
being used to train and validate machine learning algorithms [124].
While it will be challenging to advocate for data sharing and
transparency, these steps will significantly aid in accelerating the field.
Alternatively, using computationally generated databases built on
thermophysical properties obtained from CALPHAD and atomistic
properties obtained from ab initio calculations or molecular dynamics
simulations presents a promising prospect for accelerating the design of
HEAs.
3. Feedstock preparation and printability of HEAs for LPBF
3.1. Feedstock preparation
An essential aspect of LPBF-fabricated HEAs is the preparation of
powder feedstock. The technical details of the existing methods used to
prepare HEA powder have been extensively covered [14,17,56], and
only the three most prevalent techniques are introduced here.
Gas atomization (Fig. 6a) is the most common preparation technique,
yielding powder with high flowability and uniform particle size distri­
bution ideal for the LPBF process. The flowability is especially important
as a recoater, either a roller or a blade, must spread the powder uni­
formly between each melting step. Gas atomization uses pre-alloyed
HEAs or elemental ingots, which are melted and poured into an
Fig. 6. Powder preparation techniques: Schematic of the (a) gas atomization, (b) water atomization, and (c) mechanical alloying process. (d) 3d transition metal
CrMnFeCoNi powder prepared through gas atomization [125], water atomization [126], and mechanical alloying [127]. The mechanically alloyed powder is
prepared by mixing Cr, Mn, Fe, Co, and Ni elemental powders. (e) Eutectic Ni2.1AlCrFeCo powder prepared through gas atomization [128], water atomization [33],
and mechanical alloying [129]. The mechanically alloyed powder is prepared by mixing pre-alloyed AlCrFeCoNi and elemental Ni powders.
7
Materials Science & Engineering R 161 (2024) 100834
A. Jarlöv et al.
atomizer. The melt is hit by a high-pressure jet of inert gas and thus
broken into tiny droplets, then solidified into spherical and subspherical
powder particles that are screened to produce various particle size dis­
tributions. Water atomization (Fig. 6b) is a related but less common
technique in which a stream of water hits the melt, producing powder
particles with an irregular shape due to the high cooling rate compared
to when a gas jet is used. However, its economic advantage over gas
atomization warrants further investigation into its viability in preparing
HEA powder feedstock for LPBF, as long as the alloy is not prone to
reacting with the atomization medium.
Another extensively used technique for preparing LPBF powder is in
situ powder mixing, which refers to a family of techniques in which
different powders are mechanically mixed. Mechanical alloying, ball
milling, and electrodeposition are different mixing methods, among
which mechanical alloying is most commonly used to prepare HEA
powder [130]. It is a non-equilibrium solid-state fabrication technique
used to prepare powder (Fig. 6c) [130,131]. Different powders are
mixed either with or without large grinding balls in a rotating bowl, and
the continuous collisions with the grinding balls and other particles
result in deformation, welding, or fracture of the powder particles.
Eventually, the rates of welding and fracture reach an equilibrium, and
the process can result in significant refinement of the powder micro­
structure, although care needs to be taken to not excessively alter the
powder particle shape. The absence of a melting step means that me­
chanical alloying is a cost-effective preparation method where the
composition can be easily tuned, although the sphericity of the powder
particles and elemental homogeneity of the printed part may be
compromised [56]. Either all constituent elements are mixed as separate
powders, or a gas-atomized alloy is used as the base and mixed with a
secondary powder.
Figs. 6d and e compare CrMnFeCoNi and Ni2.1AlCrFeCo powders
prepared by the three techniques, while Table 1 summarizes the con­
stituent elements used in the different classes of HEAs and the methods
employed to prepare the powders. The choice of the powder preparation
technique significantly impacts the morphology and oxygen content of
the powder. Gas atomization yields high-quality spherical powder par­
ticles with a low oxygen content, which is best suited for the LPBF
process. However, the economic advantage of water atomization and
mechanical alloying make them preferred in certain aspects, particularly
for high-throughput screening, where many alloys must be prepared.
Because of the different properties of gas-atomized and mechanically
alloyed powders, the phase composition [24,132], printability [24,83],
and mechanical properties [133] of the printed parts generally depend
on the type of powder used. High-entropy matrix composites are
commonly prepared using mechanical alloying to add the extrinsic
particles, resulting in the final powder particles having a less spherical
shape than those of other classes. An exception is when the gas-atomized
HEA powder is coated by nanoparticles through the acoustic mixing
process, thereby retaining their spherical shape [27,134].
The preparation of refractory HEA powder is challenging because of
the high melting points of the constituent elements, and multiple
methods have been employed to ensure the cost-effective fabrication of
high-quality powder. Mechanical alloying is typically employed [135,
136], but because of its negative effect on the particle shape and flow­
ability of the powder, methods such as plasma spheroidization [137,
138], plasma rotating electrode process [139], and fluidization [140]
are used to alleviate these issues (Table 1). Residual refractory powder
particles in the printed parts may act as defects and compromise their
performance (Section 4.4). Notwithstanding, a recent study has
employed normalized processing maps to eliminate processing defects in
TiZrNbTa HEAs printed using mixed elemental powders, demonstrating
that it is still possible to achieve high-quality parts using mechanically
alloyed powders [141].
3.2. Printability
Although multiple AM techniques are available, LPBF is the most
widely adopted one by the industry [17], with examples of its applica­
tion ranging from parts in jet and rocket engines to implants for the
biomedical industry and heat exchangers for energy applications [17].
The LPBF process is illustrated in Fig. 7a. Before printing begins, the part
is modeled and digitally sliced into thin layers (typically 20–100 μm
thick). A recoater, either a roller or a blade, distributes uniform layers of
powder over the build platform. The laser then selectively melts the
powder to form the desired part. These steps are iterated until all the
layers have been built. The quality of the printed part depends heavily
on the process parameters used. The most influential process parameters
for LPBF are listed in Fig. 7, including the laser power P, scan speed v,
hatch spacing h, layer thickness t, rotation angle α between subsequent
layers, laser spot diameter ΦL, and scan strategy (i.e., toolpath taken by
the laser) [21].
An important metric used to optimize the printing process is the
volumetric energy density Ev, which is obtained by combining P, v, h,
and t according to
Ev =
Constituent
elements
Feedstock preparation method
3d transition metal
HEAs
Eutectic HEAs
Fe, Ni, Cr, Co, Mn, Al,
Cu, Ti, V, Si, Mo, Sm
Ni, Al, Cr, Fe, Co, Cu,
W, Mo
Co, Ni, Fe, Cr, Ti, Al,
Cu, V, Mo
Gas atomization, mechanical
alloying, water atomization
Gas atomization, mechanical
alloying, water atomization
Gas atomization, mechanical
alloying
Nb, Mo, Ta, W, Ti, Zr,
V, Ni, Cu, Co
Plasma spherodization, mechanical
alloying, gas atomization, mixing
fluidized powder
Gas atomization, mechanical
alloying
Gas atomization, mechanical
alloying, printing in reactive gas
Mechanical alloying, acoustic
mixing
Precipitationstrengthened
HEAs
Refractory HEAs
Metastable HEAs
Interstitial HEAs
High-entropy
matrix
composites
Fe, Mn, Co, Cr, Si, Cu,
Ni, C
Cr, Fe, Co, Ni, Mn, C,
N, Ti, W, Nb, Mo, Ta
Cr, Co, Ni, Fe, Mn, V,
Nb, Mo, Ta, W
(2)
Although Ev is a simplified metric that does not consider α, ΦL, or the
scan strategy, it has proved effective in optimizing the printing process
of a wide range of HEAs. For example, the tendency to form pores and
the type of pore formed (i.e., lack-of-fusion and keyhole pores) depends
heavily on Ev. Lack-of-fusion pores are highly irregular large pores
caused by insufficient Ev, while keyhole pores are small spherical pores
caused by excessive Ev [21].
However, the effect of individual processing parameters should not
be understated. Processing defects such as pores, warping, and cracks
are greatly influenced by specific processing parameters. The probabil­
ity of balling, i.e., when the melt track breaks up into liquid spheres, can
be decreased by lowering the layer thickness and scan speed, which
increases Ev, and lowering the laser power, which decreases Ev [17].
These are general guidelines, and the susceptibility to any specific
processing defect depends on the alloy system. For example, warping
generally occurs in brittle metals; thus, refractory HEAs are more sus­
ceptible to this defect [23]. The process parameters also significantly
affect the microstructure and final chemical composition of the specific
HEA. Increasing Ev reduced the lattice parameter of CrFeCoNi [142] and
CrMnFeCoNi [143] because of the preferential evaporation of Cr and
Mn, respectively.
Fig. 7b shows the Ev range used to print all classes of HEAs. As 3d
transition metal, eutectic, precipitation-strengthened, metastable, and
Table 1
Constituent elements and feedstock preparation methods, ranked from most to
least used, for the different classes of LPBF-fabricated HEAs.
HEA class
P
.
vht
8
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 7. Fundamentals of the LPBF process: (a) Process schematic. (b) Volumetric energy density Ev used to print the different classes of HEAs (only HEAs with a
reported relative density greater than 99% are included).
interstitial HEAs use similar constituent elements, the corresponding
energy density is also similar. The Ev values used to print high-entropy
matrix composites are slightly larger than the ones used to print the
other classes of HEAs, which may be attributed to the differences be­
tween their powder feedstock preparation method (Table 1). An addi­
tional motivation for using higher Ev may be to facilitate atomic
diffusion between the extrinsic particles and the matrix phase, which
results in enhanced solid solution strengthening and improved me­
chanical properties. However, higher Ev risks introducing hot cracks,
keyhole pores, and secondary phases, all of which can be detrimental to
the performance of the alloy. It is thus essential to optimize the process
parameters to allow for optimal solid solution strengthening while
ensuring the fabrication of a high-quality part. Refractory HEAs require
excessive Ev because of the high melting point of the constituent ele­
ments, notably Ta (3000 ◦ C) and W (3410 ◦ C) [144]. However, Fig. 7b
reveals that some refractory HEAs can be successfully printed using low
Ev for the lower proportion of elements with a high melting point.
Table 2 lists the process parameters of different classes of LPBFfabricated HEAs. 3d transition metal HEAs show a large processing
window [48,145], although some studies have reported the formation of
hot cracks during LPBF [22,24,110]. A CrFeCoNi HEA formed large
columnar grains (~106 μm), resulting in localized stress concentrations
and solidification cracking [22]. The authors used the Rappaz–­
Drezet–Gremaud criterion and related the grain size to the depression
pressure to show that once the grain size is below a critical value (~104
μm), the tendency to form hot cracks would be reduced. Other strategies
to reduce the cracking susceptibility are to add Al, which may form
secondary phases that can exert compressive stress and thereby suppress
crack formation [24], or reduce the stacking fault energy, which alle­
viates local stress concentrations by initiating planar stacking faults
[110].
LPBF-produced eutectic HEAs form a lamellar or cellular dual-phase
microstructure and have demonstrated excellent printability. Particu­
larly, Ni2.1AlCrFeCo HEAs demonstrate great potential, with most pub­
lications reporting a relative density of over 99.5% [32,128]. The high
printability can be attributed to the eutectic reaction being an
isothermal reaction and the cooperative solidification behavior of
eutectic HEAs. The isothermal reaction significantly reduces the solidi­
fication temperature range and practically eliminates thermal contrac­
tion, thereby reducing the tendency for solidification cracking [170].
The cooperative solidification stems from the dual-phase microstructure
in which two solutes will be rejected, each only having to diffuse to the
neighboring phase where they are incorporated into the growing solid
solution [171]. As such, the solute buildup is much smaller in eutectic
HEAs than in other dual-phase HEAs.
Alloys with a high volume fraction of precipitates may crack during
LPBF because of the intrinsic embrittlement of the material and harsh
processing conditions, i.e., rapid cyclic heating and steep thermal gra­
dients [4,172]. The practice is thus to avoid precipitation during the
printing process and instead form precipitates during the subsequent
heat
treatment
step.
Notwithstanding,
some
prominent
precipitation-strengthened HEAs, such as (FeCoNi)86Al7Ti7 [173],
AlVCrFeNi [174], and (CoNi)1.5CrFeNiTi0.5Mo0.1 [175] HEAs, have been
shown to contain L12 or L21 secondary phases and still be resistant to
cracking. Combined with the intrinsic heat treatment caused by the
layer-by-layer nature of LPBF, these observations indicate that the
reliance on subsequent post-printing heat treatment could be reduced if
the precipitation behavior can be tailored. Additional studies to eluci­
date the relationship between the process parameters and the complex
thermal history are still needed to realize in situ precipitation during
LPBF. Moreover, additional process conditions, such as substrate pre­
heating and the time between scans, should be studied as they have
shown significant influence on the thermal history of titanium alloys
[176].
It is challenging to print refractory HEAs because of the high melting
point of the constituent elements, which results in insufficient fusion of
the powder, and the brittle nature of these alloys, resulting in cracking
during the printing process. Different strategies have been employed to
improve the printability of refractory HEAs. Based on the melt pool
geometry, a pore suppression strategy was employed to fabricate a
Nb30Ta30Ti20Ni10Mo10 HEA [177]. Using a preliminary multi-­
pass–multi-layer experiment to obtain the dimension of the melt pool,
the layer thickness and hatch spacing were optimized to ensure that the
overlap between two melt pools would be equal to the layer thickness.
On the other hand, metastable HEAs can effectively prevent the propa­
gation of processing defects through localized work hardening by the
transformation-induced plasticity (TRIP) effect, thus realizing excellent
printability [25,37]. One of the challenges with LPBF-fabricated meta­
stable HEAs is to retain a sufficient amount of the metastable phase after
printing to provide work hardening during service. A high fraction of the
metastable FCC phase was retained in an Fe60Co15Ni15Cr10 HEA because
the cyclic heating during the LPBF process was sufficient to transform
the BCC structure back to the metastable FCC structure, allowing the
TRIP mechanism to be active during both printing and post-process
9
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Table 2
Process parameters used to fabricate crack-free HEAs using LPBF. RD: relative density. α: rotation angle (67◦ unless stated otherwise).
HEA
class
Chemical
composition
P
(W)
v
(mm s–1)
l
(mm)
h
(mm)
ΦL
(μm)
Feedstock type
RD
(%)
Ref.
3d transition
metal HEAs
CrMnFeCoNi
CrFeCoNi
CrCoNi
Cr35.0Fe32.5Ni32.5
AlCrFeCoNi
CrFeCoNiAl0.5
AlCrMnFeCoNi
CrFeCoNiMo0.2
CrCoNiSi0.3
Ni2.1AlCrFeCo
200
240
200
400
350
350
400
200
330
79
350
750
2000
740
600
700
1000
270
250
600
560
1000
0.05
0.04
0.04
0.04
0.05
0.04
0.05
0.07
0.06
0.025
0.04
0.085
0.05
0.04
0.12
0.11
0.09
0.10
0.09
0.1
0.08
0.08
65
75
–
90
90
90
80
90
45
–
100
99.6
99.2
99.7
99.6
–
98.4
–
–
99.12
99.5
99.5
[146]
[147]
[148]
[149]
[150]
[151]
[24]
[152]
[49]
[153]
[32]
Ni2.5AlCrFeCo
Ni2.4CrFeCoAl0.7
300
250
1000
1000
0.04
0.05
0.07
0.07
100
120
99.7
–
[154]
[155]
Precipitationstrengthened
HEAs
Ni3AlCrFeNiCu
Co30Ni30Al18Cr10Fe10Mo1W1
(FeCoNi)86Al7Ti7
(CrCoNi)94Al3Ti3
Co29.5Fe28.0Ni27.5Al8.5Ti6.5
Fe29.3Co28.7Ni28.6Al6.8Ti6.6
(CoNi)1.5CrFeTi0.3Al0.2
200
200
200
175
180
180
260
400
962
800
1000
800
800
1000
0.02
0.03
0.03
0.03
0.03
0.05
0.08
0.08
0.08
0.06
0.05
0.04
0.07
–
–
70
–
60
60
–
–
99.9
99.3
–
–
99.9
97.0
[156]
[157]
[158]
[41]
[39]
[159]
[160]
Refractory HEAs
TiNbTa0.5Mo0.2
320
500
0.03
0.06
20
–
[135]
NbMoTaTi0.5Ni0.5
300
300
0.03
0.06
–
99.9
[23]
Ti1.5ZrNbMo0.5Ta0.5
(TiZr)1.4(NbMoTa)0.6
Fe50Mn30Cr10Co10
Fe40Mn20Co20Cr15Si5
Fe60Co15Ni15Cr10
Fe34Co34Cr20Mn6Ni6
(CrMnFeCoNi)99C1
300
360
400
120
90
260
90
1000
1200
800
800
500
800
600
0.05
0.06
0.03
0.04
0.025
0.05
0.025
0.1
0.08
0.09
0.10
0.077
0.06
0.08
–
–
90
–
–
80
–
99.7
99.5
99.8
99.5
99.0
–
–
[161]
[38]
[25]
[162]
[35]
[163]
[164]
(CrMnFeCoNi)99.84N0.16
200
700
0.03
0.12
–
97.8
[165]
(NbMoTaW)99.5C0.5
CrMnFeCoNi–12 wt% TiN
400
250
200
450
0.03
0.045
0.10
0.045
–
–
99.6
99.0
[166]
[28]
CrMnFeCoNi–3 wt% TiC
CrMnFeCoNi–3 wt% Y2O3
Cr36Co32Ni32–3 wt% TiC
VNbMoTaW–4 wt% TiC
160
90
250
325
800
600
800
200
0.050
0.025
0.04
0.04
0.030
0.08
0.11
0.08
–
110
–
–
Gas-atomized
Gas-atomized
Gas-atomized
Gas-atomized
Gas-atomized
Gas-atomized
Mixed Al and CrFeCoNi (stripe scan strategy)
Gas-atomized (α = 90◦ )
Gas-atomized
Gas-atomized (α = 90◦ )
Gas-atomized (bidirectional scan strategy, α =
90◦ , printed at 80 ◦ C)
Mixed AlCrFeCoNi and Ni
Mechanically alloyed Ni6Fe1.04Cr1.02Co0.92Al0.9
and FeCo0.87Al0.86Cr0.84
Mechanically alloyed Ni and AlCrFeNiCu
Gas-atomized
Gas-atomized
Gas-atomized
Gas-atomized
Gas-atomized
Gas-atomized (zigzag scan strategy, preheated at
200 ◦ C)
Mixed elemental powders (printed at 200 ◦ C, α =
90◦ )
Mixed elemental powders
(printed at 200 ◦ C)
Gas-atomized and mixed powder
Gas-atomized
Gas-atomized
Gas-atomized
Gas-atomized (α = 180◦ , remelted)
Gas-atomized
Gas-atomized
(bidirectional strategy, α = 180◦ )
Gas-atomized in a reactive N2 gas
(chessboard strategy, α = 23◦ )
Mixed W, WC, and NbMoTa
Mixed CrMnFeCoNi and TiN (alternate hatching
strategy)
Mixed CrMnFeCoNi and TiC (α = 90◦ )
Mixed CrMnFeCoNi and Y2O3
Mixed Co32Cr36Ni32 and TiN
Mixed VNbMoTaW and TiC (substrate preheated
at 400 ◦ C for 2 h)
99.4
–
99.0
–
[167]
[168]
[26]
[169]
Eutectic HEAs
Metastable HEAs
Interstitial HEAs
High-entropy
matrix composites
deformation [35].
The addition of extrinsic particles [58,99] and interstitial elements
[101] may enhance the printability of high-entropy matrix composites
and interstitial HEAs, respectively. This phenomenon can be attributed
to faster consumption of the liquid film, more uniform defect and
thermal stress distribution, and more refined grains due to heterogenous
grain nucleation [178]. For example, the addition of TiC enhanced the
printability of Cr36Co32Ni32 [26] and VNbMoTaW [169]. The
hot-cracking susceptibility of Cr36Co32Ni32 was reduced because of
carbon diffusing into the FCC matrix and forming Cr23C6 precipitates at
the grain boundaries, thus reducing the grain boundary energy and
allowing the liquid film to be consumed. For VNbMoTaW, the addition
of 4 wt% TiC reduced the number of cracks at a given scan speed,
attributed to the ability of Ti to capture oxygen impurities, which
otherwise would embrittle the grain boundaries [169]. However, adding
excessive amounts of extrinsic particles can adversely affect printability
because of embrittlement of the matrix HEA and agglomeration of the
added particles.
Regarding the fabrication of interstitial HEAs, C and N are the most
typical elements to add to the pre-alloyed powder. N can also be added
using reactive gas during printing [31,165]. While the LPBF of (CrFe­
CoNi)98.2N1.8 resulted in crack-free parts with improved mechanical
properties [30], the presence of Mn caused elemental segregation,
thereby facilitating the hot cracking of N-doped CrMnFeCoNi compared
to the undoped alloy [179].
To summarize, the quality of the initial powder feedstock is crucial
for the performance of the final part, explaining the dominance of gasatomization. Emerging powder preparation technologies that can effi­
ciently produce highly spherical refractory HEA powder with a desirable
size distribution are needed. Achieving this may enable the fabrication
of refractory HEAs at a lower Ev, thus broadening the range of suitable
process parameters and facilitating greater control through the proc­
ess–microstructure–property relationship. Regarding the printability of
the other HEA classes, developing strategies to mitigate cracking in 3d
transition metal HEAs, in situ tailoring of precipitates in precipitatestrengthened HEAs, and retaining the metastable microstructure after
printing for metastable HEAs are essential aspects that warrant further
investigation.
4. Microstructure of LPBF-fabricated HEAs
Different design strategies have resulted in seven unique classes of
LPBF-fabricated HEAs, each displaying different mechanical, physical,
and chemical properties stemming from vastly distinct microstructures.
The microstructure for different alloys within the same class might also
differ significantly because of variations in the composition, printing
10
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
process, and post-printing thermo–mechanical treatment. This section
reviews the microstructure of 3d transition metal HEAs, eutectic HEAs,
precipitation-strengthened HEAs, refractory HEAs, metastable HEAs,
interstitial HEAs, and high-entropy matrix composites. A summary of all
seven classes is given at the end of this section.
Mn and Ni are the elements that tend to segregate into interdendritic
regions [180] or at cellular boundaries [143] because of their higher
diffusion coefficients. Secondary phases that may form during the
printing of CrMnFeCoNi include the σ phase and HCP martensite phase.
The high density of grain boundaries compared to that in conventionally
fabricated counterparts facilitates the formation of the tetragonal σ
phase because of enhanced atomic diffusion [143]. The martensite
phase forms as a result of the high dislocation density, enabling Shockley
partials to propagate along alternate slip planes [181].
The Ev value plays a major role in determining the grain texture of
the CrMnFeCoNi HEA. As Ev increases, the grain size grows, and the
preferred texture changes in the order of <233>, <001>, <203>, and
<101> along the build direction, which is linked to the shape of the melt
pool [188]. Additionally, the grain texture can be affected by the scan
strategy [180,182], rotation angle [186], and location in the printed
part [185]. This phenomenon can be understood by acknowledging that
the grain texture of LPBF-fabricated alloys aligns with the largest ther­
mal gradient, and different thermal gradients are created as the laser
turns, stops, or continues forward.
A bidirectional scan strategy results in columnar grains with an
alternating grain orientation [182] while a chessboard scan strategy
results in fewer columnar grains [180]. A 0◦ or 90◦ rotation angle results
in a <001> texture along the build direction, while only a weak texture
can be observed for a 67◦ rotation angle [186]. These observations are
4.1. 3d transition metal HEAs
3d transition metal HEAs, consisting of elements such as Cr, Mn, Fe,
Co, Ni, and Cu, represent the most widely investigated class of HEAs.
The equiatomic CrMnFeCoNi HEA is the most extensively studied HEA
for LPBF applications, exhibiting a complex hierarchical microstructure
that includes fusion boundaries [147], nanocrystalline grains [147],
elemental segregation [180], secondary phases [143,181], cellular
dislocation structures [147], and deformation twins [181] (Fig. 8). The
variations in microstructures reported in the literature can be attributed
to differences in the powder feedstock and processing parameters. Most
as-printed alloys form a single FCC phase with a homogeneous elemental
distribution [182–186] while a dendritic microstructure has been
observed in some cases [180]. This dendritic structure can be explained
by a low Ev value, which, according to the constitutional supercooling
criterion, results in a lower ratio of the thermal gradient to growth rate
[187]. As this ratio decreases, the microstructure is predicted to transit
from planar to cellular and finally to dendritic.
Fig. 8. Hierarchical microstructure of as-printed CrMnFeCoNi HEAs showing (a) fusion boundaries [147], (b) grain boundaries [147], (c) cellular dislocation
structures [181], (d) elemental segregation and MnO precipitates [180], (e) dislocation pile-ups and tetragonal σ phase precipitates [143], (f) deformation twins
[181], (g) stacking faults (indicated by arrows) [181], and (h) FCC-to-HCP phase transformation [181].
11
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
similar to those seen in the LPBF of conventional alloys and imply that
different scan strategies must be combined to fabricate industrial parts
with complex geometries.
Within the Cr–Mn–Fe–Co–Ni compositional space, multiple other
HEAs have also been prepared by LPBF, including CrFeCoNi [22,148,
189], CrCoNi [145], CrFeNi [150], CrMnFeNi [190], and Ni35C­
o23Cr21Fe21 [142]. The equiatomic CrFeCoNi HEA showed the forma­
tion of a single-phase solid solution over a wide process parameter
window. The laser power was reported to be the most crucial process
parameter for achieving fully dense parts, followed by the scan speed
and hatch distance [189]. Similar to the CrFeCoNi HEA, the ternary
CrCoNi HEA also forms a single FCC phase with homogeneous elemental
distribution after printing (Fig. 9a), but with a better build quality than
CrFeCoNi [145,149]. However, CrMnFeNi, CrFeNi, and Ni35C­
o23Cr21Fe21 HEAs exhibit elemental segregation, highlighting the
importance of the chemical composition on the elemental distribution
(Figs. 9b–d) [150,190]. In the case of Ni35Co23Cr21Fe21, Cr- and Fe-rich
BCC phases were observed in the FCC matrix phase, attributed to the
original BCC structure of these elements [142].
Several attempts have been made to add elements to the
Cr–Fe–Co–Ni HEA, significantly affecting the as-printed microstructure.
Al is among the most common elements to add for its ability to stabilize
the BCC phase [110]. A consequence of adding Al to the CrFeCoNi HEA
is reduced crack susceptibility during printing [24]. At higher Al con­
tent, a B2 honeycomb network is formed, endowing the alloy with
intrinsic toughening during deformation [191]. An equiatomic AlCrFe­
CoNi HEA printed using gas-atomized powder solidified into B2
(ordered BCC phase) and disordered BCC phases because of the rapid
solidification rate [151,192]. The Cr atoms underwent elemental
segregation, causing the formation of Cr- and Fe-rich precipitates with
nanoscale chemical fluctuations.
A newly developed Co-free Fe2Ni2AlCr HEA has been investigated for
the LPBF process [193,194]. A pioneering study on this alloy reported a
duplex BCC and FCC microstructure where the phase composition could
be fine-tuned to achieve the desired mechanical properties [193]. In
another study, LPBF-fabricated Fe2Ni2AlCr formed a single B2 phase
that decomposed at 850–1050 ◦ C [194]. However, its low printability
limited the assessment of the mechanical properties because of the for­
mation of a brittle metastable BCC microstructure that is susceptible to
crack formation. To address this issue, the composition was tuned to
Fe2.1Ni2.1Al0.9Cr0.9 via mechanical alloying [83]. The reduced Al content
shifted the primary solidification path from the BCC phase to the FCC
phase, thereby preventing hot cracking. The FCC phase decomposed into
an FCC matrix rich in Cr and Fe and an ordered BCC phase rich in Al and
Ni after a heat treatment at 850 ◦ C for 6 h (Fig. 10a).
Another alloy system investigated for LPBF is Al–Cr–Fe–Co–Ni–Cu
[195]. While the equiatomic HEA demonstrates Cu segregation and a
duplex FCC and BCC microstructure [195], omitting Cr results in a single
BCC phase [196]. If Co is instead omitted, the HEA will consist of
disordered and ordered BCC phases, as well as nanosized Cu-rich pre­
cipitates [197]. A CrFeCoNiCuAl0.3 HEA demonstrated a single FCC
phase [198], indicating that the high Al content stabilized the BCC phase
in AlCrFeCoNiCu, AlFeCoNiCu, and AlCrFeNiCu. However, all the alloys
were highly prone to cracking, highlighting the challenge of using them
Fig. 9. Phase composition of LPBF-fabricated Cr–Mn–Fe–Co–Ni HEAs: (a) Electron backscatter diffraction (EBSD) image of a CrCoNi HEA showing a single FCC
lattice structure [145]. The inset shows the X-ray diffractogram (XRD), revealing that the CrCoNi alloys fabricated using high (H), medium (M), and low (L) laser
power all consist of a single FCC structure. (b) Transmission electron microscope (TEM) image and (c) energy dispersive spectroscopy (EDS) maps of LPBF-fabricated
CrMnFeNi [190]. (d) Atom probe tomography (APT) image of a CrFeNi HEA, revealing the Cr- and C-rich precipitates [150].
12
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 10. Microstructural features of LPBF-fabricated 3d transition metal HEAs: (a) Phase composition before and after annealing the Fe2.1Ni2.1Al0.9Cr0.9 HEA [83].
(b) Scanning transmission electron microscopy (STEM) image showing nanosized inclusions (left) and an atom reconstruction map revealing the compositional
difference among the FCC matrix, σ phase, Ni-rich precipitate, and Cr–S inclusion (right) in a CrCoNiSi0.3 HEA [153]. Microstructure of a CrFeCoNiMo0.2 HEA near
(c) the center of the melt pool and (d) the melt pool boundary [49].
in LPBF applications due to the high phase fraction of the brittle BCC
phase. The composition of Al–Cr–Fe–Co–Ni–Cu HEAs requires further
optimization for use in LPBF. Minimizing the Al content could prevent
the formation of the brittle BCC phase and warrants investigation as
alloys of such composition show great promise as thermomagnetic parts
[199], antibacterial materials [200], and Invar alloys [201]. Another
solution is to add extrinsic nanoparticles that refine the microstructure
as the finer grains can more easily accommodate localized stress con­
centrations and promote a phase transformation from the brittle phase
to a more ductile one.
Other elements added to 3d transition metal HEAs include Si [82,
153], Cu [200], Ti [202], and Mo [49]. The addition of 1.5 at% Si to a
CrFeCoNi HEA results in the formation of a single FCC phase [82] while
a higher Si content in a CrCoNi HEA (~9 at%) leads to the formation of σ
phases rich in Cr and Si, Ni-rich precipitates, and Cr–S inclusions
(Fig. 10b) [153]. Moreover, the addition of Si induces novel dislocation
structures in the as-printed material, including planar defects [153] and
dislocation loops [82], which are attributed to the reduction in stacking
fault energy. Cu tends to segregate during the LPBF process, and me­
chanically alloyed CrFeCoNi and Cu powders with poor mixing can
result in unmelted Cu-rich particles [203]. However, successfully mixed
powders can yield an HEA with homogenous elemental distribution
[200], indicating that gas-atomized CrFeCoNiCu powder will further
facilitate the formation of a single FCC phase. Upon adding Ti, its high
melting point may result in unmelted Ti particles when in situ mixed
powder is used [203] while gas-atomized (CoNi)1.5CrFeTi0.5Mo0.1
powder shows homogeneous elemental distribution with no secondary
phases [202]. The addition of ~4.8 at% Mo to CrFeCoNi caused the
precipitation of a Mo-rich phase near the melt pool boundaries, while
the center of the melt pool remained precipitate-free (Figs. 10c and d)
[49].
reaction, while other elements result in constitutional supercooling,
which destabilizes the planar eutectic solidification front [206]. Eutectic
HEAs were recently prepared using the LPBF technique and have quickly
become a hot research area due to the ease of fabricating crack-free parts
over a wide process parameter window [157,207]. Coupled with the
rapid solidification rate of LPBF and potential heat release when
different elements mix, LPBF-fabricated eutectic HEAs span a wide
range of microstructures, including metastable solidification cells [33,
207] and eutectic lamellas [129,133].
Ni2.1AlCrFeCo is the first eutectic HEA introduced [170] and has
been extensively studied for LPBF applications for its high printability
and impressive mechanical properties [129,207,208]. The steep thermal
gradient in LPBF allows for an ultrafine microstructure, with the BCC
and FCC lamellas having widths of 64 and 151 nm, respectively, and an
interlamellar spacing of 90–215 nm [129]. By controlling the scan angle
and partial remelting to induce epitaxial growth with multiple prefer­
ential growth orientations, an architected microstructure is achieved,
consisting of eutectic colonies with a close-to-random orientation [32].
The BCC lamellas exhibit an even more complex structure, with APT
maps revealing the formation of regions rich in either Al and Ni or Cr, Fe,
and Co (Fig. 11a).
Ni2.1AlCrFeCo was also prepared by large-volume LPBF printing,
with a build volume of ~17600 mm3 in contrast to the standard 7 × 7 ×
7 mm3 cubes typically prepared [33]. The as-printed HEA consisted of a
large fraction of the FCC phase (88 vol%) rich in Cr, Fe, and Co, with
slices of B2 phases rich in Al and Ni between the FCC cells, which is in
contrast to previous work where no precipitates were formed for
LPBF-fabricated Ni2.1AlCrFeCo [32]. This discrepancy can be explained
by the faster solidification arising from using lower laser power [33] and
faster heat dissipation in a larger part, resulting in non-equilibrium
conditions where solutes can segregate to the cell boundaries to form
the secondary phases. High-resolution STEM further revealed the exis­
tence of nanosized precipitates with a Cr content of ~55 at% in the B2
phase (Fig. 11f).
Other studies have demonstrated that decreasing the solidification
time, by reducing Ev, changes the morphology from a lamellar to a
cellular structure (Fig. 11e) [129] while also increasing the fraction of
the FCC phase [208,209]. The change in microstructure can be
4.2. Eutectic HEAs
Eutectic HEAs have composition close to a eutectic point in the phase
diagram, yielding a dual-phase microstructure (HEAs with hyper- [155]
and hypo-eutectic [204,205] composition are also included in this
class). Only a few constituent elements are required for the eutectic
13
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 11. Microstructural features of LPBF-fabricated Ni2.1AlCrFeCo: (a) High-angle annular dark field (HAADF) image and APT maps showing the modulated
nanostructures within the BCC lamellae [32]. (b) HAADF image showing the interface between the FCC and B2 phases [33]. Fast Fourier transform images of the (c)
FCC and (d) B2 phases. (e) Effect of the laser power and scan speed on the microstructure of Ni2.1AlCrFeCo [129]. (f) STEM EDS analysis showing the elemental
distribution at the interface in (b).
explained by the constitutional supercooling criterion, where a
decreasing ratio of the temperature gradient over growth rate results in
the interface morphology changing from planar to cellular and finally to
dendritic [187]. Thus, the decrease in the laser power and increase in the
scan speed can change the morphology from a planar to a cellular one.
Additionally, the change in phase composition can be ascribed to the
fact that the BCC phase will grow in its ordered state for most super­
cooled conditions, which is kinetically unfavored compared to the
growth of the disordered FCC phase [210]. As such, the supercooled
condition, caused by decreasing Ev, will favor the growth of the FCC
phase over the BCC phase.
The effect of gas-atomized, mechanically alloyed, and recycled
powders for fabricating eutectic Ni2.1AlCrFeCo has been investigated,
revealing that vastly different microstructures, and thus mechanical
properties can be achieved depending on the type of powder feedstock
used [128,133]. The gas-atomized powder used in ref. [133] formed a
lower fraction of the FCC phase and a metastable cellular microstructure
while the in situ mixed powder showed a higher fraction of the FCC
phase and a near-eutectic microstructure (Figs. 12a and b). The differ­
ence in the phase fraction was attributed to the high enthalpy of mixing
for Al and Ni elements. TEM–EDS revealed an FCC–B2 phase boundary
rich in Al and Ni for the pre-alloyed powder (Fig. 12c). This phenome­
non was attributed to the low diffusion rate of these elements in the B2
phase compared to the FCC phase, resulting in the accumulation of Al
and Ni as they diffused to form the eutectic microstructure.
The mechanically alloyed powder showed different elemental
composition for the two phases (Fig. 12d) due to regions with elemental
fluctuations acting as nucleation sites for the FCC and B2 phases, and the
enthalpy of mixing provided heat for sufficient diffusion to occur.
Recycling the powder at least four times caused Al-rich oxides to attach
to the surface of the powder [128]. These impurities disrupted the
lamellar growth, thus yielding a cellular microstructure in addition to
the lamellar structure [128]. Further elucidating the relationship be­
tween impurities in the recycled powder and the formed microstructure
is of particular importance in reducing material waste and realizing
manufacturing processes with low environmental impact.
Other eutectic HEAs prepared by LPBF include Ni2.1CrFeAl0.75 [204],
Co30Ni30Al18Cr10Fe10MoxWy [32,91,157], CrMnFeCoNiTi0.6 [211], and
NiyCrFeCuAlx [212–214]. Most of these alloys are designed around the
Ni–Al eutectic point. Although multiple examples of conventionally
14
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 12. Effect of using different Ni2.1AlCrFeCo powder: TEM–EDS maps showing the elemental distribution of the (a) pre-alloyed and (b) mechanically alloyed
powders [133]. Elemental distribution of dual-phase HEAs and a schematic solidification diagram for the (c) pre-alloyed and (d) mechanically alloyed pow­
ders [133].
Fig. 13. Effect of chemical composition on eutectic HEAs: microstructure of (a) CrMnFeCoNiTix HEAs (0≤ x ≤1.0) [211], (b) Ni2CrFeCuAlx HEAs (0≤ x ≤1.0) [213],
and (c) NiyCrFeCuAl HEAs (2.0≤ y ≤3.0) [214].
15
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
fabricated eutectic HEAs exist, the challenge of fabricating high-quality
LPBF powder feedstock may act as an obstacle to exploring their
viability in LPBF.
Crack-free Co30Ni30Al18Cr10Fe10Mo1W1 samples could be fabricated
by LPBF under a large processing window, and the eutectic micro­
structure showed a refined lamellar spacing of 150–200 nm and lamellar
colonies with a size of 2–6 μm [157]. Adding Ti to a CrMnFeCoNi HEA
resulted in a eutectic dual-phase microstructure, which can successfully
reduce the cracking susceptibility during LPBF by transforming the re­
sidual tensile stress into compressive stress, thus closing the formed
cracks (Figs. 13aI–III) [211]. However, an excessive Ti content resulted
in an abundance of the brittle BCC phase and promoted hot cracking
(Fig. 13aIV).
For NiyCrFeCuAlx, the content of Ni and Al plays a vital role in
influencing the phase composition. A Ni2CrFeCuAl HEA comprised a
large fraction of the BCC/B2 phase, with noodle-like precipitates and a
basket weave microstructure (Figs. 13bI and cI) [213,214]. The BCC/B2
phase also contained nanosized Cr–Fe precipitates. Decreasing the Al
content reduced the BCC/B2 phase and caused an equiaxed-to-columnar
transition as the BCC/B2 phase hindered the columnar growth of FCC
grains and acted as heterogeneous nucleation sites (Figs. 13bI–IV).
Conversely, increasing the Ni content changed the primary solidification
structure from the BCC/B2 phase to the FCC phase (Figs. 13cI–IV) [214].
A near-eutectic microstructure was obtained for the Ni2.5CrFeCuAl HEA
(Fig. 13cII), while a higher Ni content yielded a hypoeutectic micro­
structure where the ordered B2 phase contained spherical disordered
BCC precipitates (Figs. 13cIII and IV).
The importance of Ni and Al on the phase composition can be
explained as they are the main stabilizers of the constituent phases, i.e.,
the FCC and BCC phases, respectively. They dictate the eutectic
composition and are thus present in almost every LPBF-fabricated
eutectic HEA. Designing novel eutectic HEAs around other eutectic
points, such as Al–Fe and NiTi–Nb, is a promising avenue to expand the
palette of LPBF alloys. Other challenges in the fabrication of eutectic
HEAs for LPBF lie in achieving higher cooling rates to refine the
microstructure further and investigate its effect on the phase composi­
tion. The cooling rate affects the phase composition in different ways
depending on the rate. Initially, a high cooling rate favors the growth of
the FCC phase, but as the cooling rate exceeds a critical point, it will
favor the formation of the BCC phase with the transition from ordered to
disordered BCC phases [210]. This raises questions regarding what
would happen if an LPBF technique with a higher cooling rate is
employed, e.g., pulsed-wave LPBF [215].
Fig. 14. Electron microscope images of precipitation-strengthened HEAs
fabricated by LPBF: (a) (FeCoNi)86Al7Ti7 [158,217], (b) (CoNi)1.5CrFeTi0.3Al0.2
[160], and (c) (CrCoNi)94Al3Ti3 [41]. (I) As-built HEAs. (II) and (III)
Heat-treated HEAs.
elements with a high affinity for oxygen, such as Al and Ti [217]. In
addition to the Al–Ti–Cr–Fe–Co–Ni HEAs heavily inspired by Ni-based
superalloys, other LPBF-fabricated precipitation-strengthened HEAs
include Cu-containing Cu36Mn25Ni23Co9Cr7 [218] and CrFeCoNiCuAl0.3
[219], which are strengthened by the CrCo- and Cu-rich precipitates,
respectively. The driving force for the formation of secondary phases is
the difference in the mixing enthalpies between the constituent ele­
ments, leading to spinodal decomposition during aging.
A critical step for fabricating high-strength precipitation-strength­
ened HEAs is the post-printing heat treatment, during which the pre­
cipitates are formed. The cellular dislocation network formed during the
LPBF process promotes the formation of precipitates after direct aging,
as the cell walls can facilitate atomic diffusion [39]. In contrast,
conventionally manufactured precipitation-strengthened HEAs require
an annealing step before aging to achieve desirable mechanical prop­
erties [160]. Similar to the aged (CoNi)1.5CrFeTi0.3Al0.2 HEA, (FeCo­
Ni)86Al7Ti7 also contains both L12 and L21. The presence of precipitates
is heavily influenced by the aging temperature and time. For example,
within an aging time of 0.5 h, only L21 structured precipitates form in
(CrCoNi)86Al7Ti7 (Fig. 14aII) at a similar temperature as those for
(CoNi)1.5CrFeTi0.3Al0.2 (Fig. 14II) and (FeCoNi)94Al3Ti3 (Fig. 14cII). In
contrast, a higher annealing temperature is required to form L12 pre­
cipitates for a short aging duration (Fig. 14cIII). The duration of the
aging treatment may vary for different HEAs, ranging from 2 h for
(FeCoNi)86Al7Ti7 to 50 h for (CoNi)1.5CrFeTi0.3Al0.2 (Figs. 14aIII and
bIII) [158,160]. The heat treatment still needs to be optimized for the
specific composition to allow for the best performance.
Precipitates contribute to the main strengthening mechanism of
(FeCoNi)94Al3Ti3, and the highest strength was achieved at 800 ◦ C when
the heat treatment was performed in the temperature range of 500–1100
◦
C [41]. This phenomenon was attributed to the dissolution of the
dislocation network, regardless of the formation of a higher volume
fraction of L12 at higher temperatures (Fig. 15a). Similar results were
obtained when a homogenization heat treatment was applied to an
LPBF-fabricated (FeCoNi)86Al7Ti7 HEA [220], highlighting the trade-off
between the two strengthening mechanisms and the challenge of
4.3. Precipitation-strengthened HEAs
Because of the multi-element nature of HEAs, several secondary
phases can form depending on the chemical composition [63]. While
some of these phases can be detrimental, precipitation-strengthened
HEAs can achieve an optimal distribution and volume fraction of sec­
ondary phases through intricate alloy design and post-processing to
realize outstanding mechanical properties. This section focuses on
precipitation-strengthened HEAs from the Al–Ti–Cr–Fe–Co–Ni system
containing a high volume fraction of L12 precipitates to optimize the
strength–ductility synergy [76,216]. Additionally, some alloys beyond
the Al–Ti–Cr–Fe–Co–Ni system, which are designed to contain similar
phase composition (i.e., an FCC matrix with dispersed L12 precipitates)
are included in this class.
Currently, three main groups of precipitation-strengthened HEAs
have been investigated for LPBF applications: Al–Ti–Fe–Co–Ni [158,
217], Al–Ti–Cr–Fe–Co–Ni [160], and Al–Ti–Cr–Co–Ni [41], with
representative HEAs shown in Fig. 14. The latter two form a single FCC
phase in their as-printed state, while the former tends to form an FCC
and
L21
dual-phase
microstructure
(Figs.
14aI–cI).
Precipitation-strengthened HEAs are prone to segregation in the inter­
dendritic regions and formation of oxides because of the inclusion of
16
­
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 15. Effects of heat treatment on precipitation-strengthened HEAs: (a) Schematics of the microstructural evolution and deformation mechanisms of a (CrCo­
Ni)94Al3Ti3 HEA for the as-printed and annealed samples at 500, 800, and 1100 ◦ C [41]. (b) Scanning electron microscope (SEM) and (c) STEM images of
LPBF-fabricated Co29.5Fe28.0Ni27.5Al8.5Ti6.5, revealing the presence of L12 (yellow arrows) and L21 phases (blue arrows) and a high number of dislocations (red
arrows) [39].
designing an optimal heat treatment strategy.
Nonetheless, the annealing at 780 ◦ C for 4 h of LPBF-fabricated
Fe28.0Co29.5Ni27.5Al8.5Ti6.5 resulted in a dislocation–precipitate skel­
eton within which the ordered L12 phase formed (Figs. 15b and c) [39].
The dislocation network exhibited multiple barriers for further defor­
mation, including the anti-phase boundaries and dislocation network
structure. While precipitation-strengthening is the dominant strength­
ening mechanism, careful consideration is required to minimize the
disruption of the formed dislocation network to further improve the
mechanical performance. Additionally, the stability of both the pre­
cipitates and dislocation network must be evaluated at elevated tem­
peratures,
considering
the
intended
applications
of
precipitation-strengthened HEAs (Section 6).
HEAs.
The printing of alloys containing elements with different melting
points results in the formation of a dendritic microstructure due to the
elements with low melting points solidifying last (Fig. 16). A Ti-rich
interdendritic microstructure was formed in as-printed TiMoWTa
[140] while Ti1.4Zr1.4Nb0.6Mo0.6Ta0.6 [38], Ti1.5NbZrMo0.5Ta0.5 [161,
223], and Ti28.33Zr28.33Hf28.33Nb6.74Ta6.74Mo1.55 [224] exhibited an
interdendritic microstructure rich in both Ti and Zr. Alloying NbMoTa
with Ti or Ni caused the segregation of the alloying element to the
interdendritic regions [23]. While potentially problematic, this phe­
nomenon is generally suppressed compared to the case of refractory
HEAs fabricated by conventional processing routes because of the rapid
cooling rate [38].
The printing process of refractory HEAs containing elements with a
high melting point is challenging, even when high-quality powder is
used. Although spherical VNbMoTaW powder particles were produced
using the radio frequency plasma spheroidization method, several pro­
cessing defects remained in the as-printed HEA, including pores,
unmelted particles, and cracks [137]. Although the pores and unmelted
particles could be mitigated by optimizing the scan speed, the cracks
persisted because of high residual stress induced by the printing process
and the brittle nature of VNbMoTaW. Conversely, refractory HEAs
containing a low content of elements with a high melting point (i.e., W
and Ta) have been printed with no cracks, low porosity, and limited
elemental segregation [38,224], which can be attributed to the more
narrow freezing temperature range suppressing solidification cracks.
Adding 3d transition metal elements such as Ni, Co, and Cu to re­
fractory HEAs may result in complex phase composition. A Ti25Zr25
Ni25Cu15Co10 HEA contained multiple phases, including a BCC-
4.4. Refractory HEAs
Refractory HEAs consist of refractory elements (i.e., Ti, V, Zr, Nb, Mo,
Hf, Ta, and W). Due to their high melting point, strength, and corrosion
resistance, refractory HEAs are commonly regarded as suitable materials
for high-performance applications at elevated temperatures. Addition­
ally, their high biocompatibility makes them promising candidates for
the medical industry [221,222]. However, similar to the Ti-based alloys,
refractory HEAs are challenging to be machined into a desired shape
because of their high hardness [2], limiting their industrial adoption.
The unique advantage of LPBF in fabricating intricate parts in a single
step may solve this challenge, although the high melting point and
limited ductility of refractory HEAs typically result in the formation of
processing defects [23,137]. Creative alloy design and careful process
optimization are thus necessary to improve the printability of refractory
Fig. 16. SEM micrograph and EDS maps of LPBF-printed TiMoTaW [140].
17
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
structured TiNi matrix phase, Laves phases, and zirconium oxides [138].
The formation of ZrO and ZrO2 was attributed to residual impurities in
the feedstock material and contamination during the LPBF process.
However, the formation of secondary phases with lower stacking fault
energy can mitigate the cracking behavior during the printing process.
For instance, Ti and Ni have been added to NbMoTa to investigate their
effect on the printability and mechanical properties of the as-printed
alloy (Fig. 17) [23]. The equiatomic alloys showed limited ability to
accommodate plastic deformation during printing and contained cracks,
while crack-free components of NbMoTaTi0.5Ni0.5 were successfully
fabricated. This was attributed to the low stacking fault energy of the
monoclinic Ni3Ta(Ti, Nb, Mo) phase, which formed at the grain
boundaries of NbMoTaTi0.5Ni0.5 and absorbed the excess thermal stress
through the formation of extended dislocations (Fig. 17f).
While multiple challenges are associated with printing refractory
HEAs, their unique properties make them strong candidates for use in
numerous challenging environments. The strategies discussed to
enhance printability—such as balancing the number of elements with
high melting points and introducing non-refractory elements—hold
significant potential for discovering new high-performance LPBF alloys.
Another promising approach is to use refractory HEAs as a matrix phase
for interstitial HEAs and high-entropy matrix composites, which will be
further elaborated on in the later sections.
change can be attributed to the vastly different thermal properties of Si
compared to those of the other constituent elements.
An Fe60Co15Ni15Cr10 HEA exhibited a heterogeneous grain structure,
high-angle grain boundaries, cellular structures, and compositional
heterogeneities with Fe-rich cell cores and cell boundaries rich in Cr and
Ni (Fig. 19) [35]. Along the build direction, the grains appeared to form
a bimodal size distribution due to the grains growing along the largest
thermal gradient. As such, grains growing perfectly aligned with the
build direction, i.e., with a <100> orientation, appeared as thin grains,
whereas grains growing diagonally from the melt pools, i.e., with a
<110> orientation, appeared as columnar grains.
The mechanical properties of metastable HEAs can be adjusted by
adding extrinsic particles [227] or alloying elements [37,228], both of
which affect the microstructure and phase composition. Adding 4 wt%
B4C changes the HEA to a high-entropy matrix composite, which is
discussed in the subsequent section. Alloying elements used include C
(turning the alloy into an interstitial HEA), Si, Cu, Al, and Ti. Adding
1.5 at% Cu to the Fe40–xMn20Co20Cr15Si5Cux HEA suppresses the TRIP
mechanism during printing, resulting in the formation of microcracks,
which can be attributed to Cu being a strong FCC stabilizer. Notwith­
standing, the alloy demonstrated an impressive damage tolerance as the
strength increased regardless of the microcracks. Al and Ti also sup­
pressed the TRIP mechanism of (Fe50Mn30Cr10Co10)100–2xAlxTix during
the printing process, which was attributed to the formation of Al- and
Ti-rich secondary phases [228].
As mentioned above, the TRIP mechanism yields excellent print­
ability for metastable HEAs [225,226]. A metastable Fe50Mn30Cr10Co10
HEA exhibited better printability than CrMnFeCoNi using the same
process parameters due to the TRIP mechanism alleviating residual
stress [25]. However, it is essential to consider how much of the meta­
stable microstructure can be retained during the LPBF process, as the
already transformed microstructure cannot provide work hardening
during deformation. The rapid cooling rate in LPBF may retain a higher
fraction of the metastable phase than the lower cooling rate in con­
ventional processing techniques (Figs. 20a and b). Additionally,
compositional design can further tune the tendency to undergo TRIP
during the printing process (Figs. 20 c–j) [37,227].
As will be highlighted in the subsequent sections, LPBF-fabricated
metastable HEAs possess inferior yield strength compared to the other
classes as the TRIP mechanism is only active after plastic deformation is
initiated. Notwithstanding, metastable HEAs have multiple avenues to
achieve competitive niches due to their high printability and unique
properties. In particular, their compositional similarity to LPBFfabricated Fe–Mn–Si–Cr–Ni shape memory alloys makes them prom­
ising materials for four-dimensional (4D) printing (Section 6.4) [229,
230].
4.5. Metastable HEAs
Metastable HEAs contrast with the conventional HEA design
concept, which aims to stabilize a single solid solution phase by
increasing the entropy. Instead, metastable HEAs increase the meta­
stability of the alloy to promote the TRIP effect during deformation.
When fabricated by LPBF, these alloys form a metastable FCC phase,
which transforms into an HCP [36,225] or BCC structure [35] when
subjected to a sufficiently high local strain. The TRIP mechanism en­
hances the damage tolerance of metastable HEAs and allows them to
resist the formation of common processing defects such as
micro-cracking. When the area ahead of the crack tip is subjected to
stress concentration, the initial FCC structure undergoes the TRIP
mechanism to provide localized work hardening (Figs. 18a and b) [37].
Metastable HEAs fabricated by LPBF show a hierarchical micro­
structure with heterogeneity spanning several length scales. Near-fully
dense Fe50Mn30Cr10Co10 and Fe49.5Mn30Cr10Co10C0.05 were fabricated
with a hierarchically heterogeneous microstructure similar to that in 3d
transition metal HEAs (Figs. 18c–e). The introduction of 3 at% Si to
Fe50Mn30Cr10Co10 changed the grain growth orientation from <101> to
<100> and <111> along the build direction, and a random orientation
was observed when 5 at% Si was added (Figs. 18f–h), indicating a
change in the melt pool geometry for the different HEAs [226]. This
Fig. 17. Microstructural features of LPBF-fabricated Ti–Ni–Nb–Mo–Ta HEAs: EBSD images of (a) NbMoTa, (b) NbMoTaTi, (c) NbMoTaNi, and (d) NbMoTaTi0.5Ni0.5.
(e) Brittle fracture in the α-Ti phase of NbMoTaTi. Internal stress F denotes the stress caused by thermal contraction. (f) Stacking faults in the grain boundary
precipitate of NbMoTaTi0.5Ni0.5 [23].
18
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 18. Microstructural features of LPBF-fabricated metastable HEAs: (a) Schematic of the TRIP mechanism ahead of the crack tip. (b) Phase transformation ahead
of the crack tip in the Fe38.5Mn20Co20Cr15Si5Cu1.5 HEA [37]. Hierarchical microstructure of Fe49.5Mn30Cr10Co10C0.05 showing (c) fusion boundaries, (d) high-angle
grain boundaries (HAGBs), a cellular structure, and (e) dislocation substructures [225]. EBSD maps of (f) Fe50Mn30Cr10Co10, (g) (Fe50Mn30Cr10Co10)97Si3, and (h)
(Fe49.5Mn30Cr10Co10)95Si5 [226].
4.6. Interstitial HEAs
increasing the C content from 0.5 to 1.5 at% increased the grain size
despite a higher fraction of Cr23C6 (Fig. 21d) because of the suppression
of the intrinsic recrystallization behavior during the LPBF process. Heat
treatment of C-doped Cr–Mn–Fe–Co–Ni HEAs led to the precipitation
and growth of additional Cr23C6. The precipitation followed the Avrami
formula for CrFeCoNiC0.5 with a maximum precipitation density of
~0.33 vol% at 850 ◦ C [236].
Besides 3d transition metal HEAs, metastable Fe50Mn30Co10Cr10 and
refractory NbMoTaW HEAs were doped with C (0.5 at%) and fabricated
by LPBF [166,225]. The Fe49.5Mn30Co10Cr10C0.5 HEA demonstrated a
similar microstructure to LPBF-fabricated Fe50Mn30Co10Cr10, with no
carbide precipitation. However, a higher carbon content may trigger the
formation of Cr23C6, and its effect on the microstructure and meta­
stability requires investigation. The (NbMoTaW)99.5C0.5 HEA formed
carbides, resulting in grain refinement and increased dislocation den­
sity, as was evident from the increased misorientation angle (Figs. 21e
and f). The carbides were rich in Nb (Fig. 21g), which could be attrib­
uted to the high diffusion coefficient of Nb and low formation enthalpy
of NbC [166].
Several N-doped HEAs have been fabricated by LPBF. The addition of
N resulted in a highly heterogeneous microstructure with a bimodal
grain size distribution due to the continuous change in the N content
during printing (Figs. 22a and b). The partial remelting of previously
deposited layers led to N enrichment due to its high solubility in the melt
pool, which caused grain refinement, similar to the case of N-containing
steels [237]. When the N content was sufficiently high, evaporation of
Interstitial HEAs incorporate non-metallic elements that either
occupy interstitial lattice positions and provide solid solution strength­
ening or form precipitates and intermetallic compounds acting as grain
refiners, thus leading to Orowan and grain boundary strengthening.
LPBF-fabricated HEAs currently incorporate C and N as their nonmetallic elements.
Carbon has been added to several HEAs, including CrMnFeCoNi
[231–233], CrFeCoNi [234], NbMoTaW [166], and Fe50Mn30Co10Cr10
[225]. For Cr–Mn–Fe–Co–Ni HEAs, a bidirectional scan strategy resulted
in columnar grains growing along the build direction, while the hori­
zontal direction consisted of alternating bands of fine and coarse grains
(Figs. 21a and b) [164]. The grain interior consisted of a similar dislo­
cation network as reported for the 3d transition metal HEAs, and the size
of the dislocation cells decreased as the Ev value increased. This decrease
in the cell size λ can be understood by the greater degree of supercooling
caused by increasing Ev, resulting in a higher dislocation density ρ ac­
cording to [235]
/√̅̅̅
(3)
λ=c
ρ,
where c is a constant. The addition of carbon formed Cr23C6 precipitates
at the Mn- and Ni-enriched cell boundaries due to the accelerated
diffusion at these boundaries (Fig. 21c). These carbides disrupted the
columnar growth, resulting in grain refinement [166,236]. However,
19
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 19. Microstructural features of LPBF-fabricated Fe60Co15Ni15Cr10: (a) Pseudo-3D EBSD kernel average map and (b) SEM back-scattered electron micrograph of
the as-printed alloy showing melt pool boundaries (MPBs), HAGBs, and cell structures. (c) STEM bright field image of solidification cells. (d) Magnified STEM
micrograph for the cell boundary (left) and EDS line profiles (right) for the constituent elements across the cell boundary along the white arrow marked in the
micrograph [35].
N2 occurred, keeping the N content relatively constant throughout the
printed part [30].
The ability to select the building atmosphere during the LPBF process
(i.e., using an inert or a reactive gas atmosphere) presents an opportu­
nity for the efficient fabrication of interstitial HEAs. The printing of
CrMnFeCoNi under a reactive N2 atmosphere resulted in ordered ni­
trogen complexes (Figs. 22c and d). These complexes facilitated dislo­
cation nucleation during printing, resulting in a high dislocation density
in the as-printed samples [165]. Contrary to C addition, adding N to
CrFeCoNi and CrMnFeCoNi HEAs does not form precipitates. However,
a Cr2.5Ni2TiFeCoW0.5 HEA prepared by LPBF under a reactive N2 at­
mosphere showed precipitation of TiN due to the higher affinity of Ti for
N [31].
A high oxygen content in the powder feedstock can yield unintended
oxides in the printed part (Fig. 22e) [239,240]. While nanosized oxides
(~27.3 nm) have been reported to be beneficial for fatigue [241] and
creep resistance [125], they might impair ductility. Strategies to control
the oxide formation include minimizing the use of in situ mixed powder
with high affinity for oxygen (e.g., Mn and Ti) or purging the LPBF
machine to sufficiently low oxygen levels.
Strategies to advance LPBF-fabricated interstitial HEAs include
expanding the range of interstitial elements, combining elements with
high affinity to tune phase composition, and developing models for
accumulation of interstitial elements during partial remelting. Elements
like B and S, which have shown impressive properties in conventionally
fabricated HEAs, should be evaluated [242]. Interstitial HEAs may
contain beneficial or detrimental intermetallic phases (e.g., carbides,
oxides, and nitrides), and understanding their precipitation is essential.
One strategy is to use constituent elements with high affinity for the
interstitial atoms. Partial remelting can lead to accumulation of inter­
stitial elements, affecting grain morphology. While similar phenomena
are well understood in steels, the complexity of LPBF-fabricated HEAs
requires deeper study in order to reliably fabricate alloys with desired
performance.
4.7. High-entropy matrix composites
High-entropy matrix composites enhance the hierarchical heteroge­
neity of LPBF-fabricated HEAs by adding extrinsic particles. Because of
the ease of mixing different powders during mechanical alloying in the
20
­
­
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 20. Phase evolution of LPBF-fabricated metastable HEAs: (a and b) EBSD phase maps and XRD diffractogram of as-printed and as-cast Fe40Mn20Co20Cr15Si5,
respectively [36]. (c–h) EBSD phase maps of (c–f) (Fe50Mn30Co10Cr10)97Si3 (g–h) and (Fe50Mn30Co10Cr10)95Si5 HEAs at a strain of 0% (c and g), 8% (d and h), 16% (e
and i), and 24% (f and j) [226].
feedstock preparation step, micro- and nanosized particles have been
added to several HEAs. The most commonly added particles include TiC
and TiN, while WC, pure W, Y2O3, SiC, etc. are also used.
TiC has been added to 3d transition metal [167,243] and refractory
[169] HEAs. The addition of extrinsic particles results in grain refine­
ment, attributed to heterogeneous grain nucleation and the restricted
growth of columnar grains [244]. The distribution of strengthening
particles can be tuned using the scan speed: high scan speeds result in
atomic Ti and C solutes while low scan speeds could cause the growth of
TiC precipitates [243]. TiC can also affect the elemental distribution and
suppress the formation of MnO because of the higher oxygen affinity of
Ti than Mn, thus resulting in a homogenous elemental distribution
(Figs. 23a and b) [167]. However, a low TiC content may result in
elemental segregation (Fig. 23c). For Cr36Co32Ni32, the addition of 3 wt
% TiC resulted in the diffusion of carbon into the FCC matrix and the
formation of Cr23C6 precipitates at the grain boundaries (Fig. 23d), thus
reducing the grain boundary energy and mitigating cracking during the
printing process.
TiN also acts as a strong grain refiner [244,245]. The addition of 5 wt
% TiN to CrMnFeCoNi results in a grain size of 3.5–5 μm. Further
addition (12 wt%) reduced the grain size to less than 2 μm and increased
the misorientation angle between grains, indicating an increased dislo­
cation density (Figs. 24a and b) [28]. This phenomenon can be
explained by the dissolution of TiN and formation of interstitial N, which
enhances dislocation activities, similar to the case of interstitial HEAs.
Microregions of amorphous phases have been reported in a CrMnFeCoNi
HEA containing 5 wt% TiN (Figs. 24c–e) [245], further corroborating
that interstitial N leads to extensive dislocation activities. The
amorphization has significant implications for the fabrication of
high-performance HEAs as forming amorphous shear bands can improve
the plasticity under extreme deformation conditions [246,247].
Several other extrinsic particles have been added to 3d transition
metal HEAs, including Y2O3 [168], TiB2 [249], TiAl [250], bulk metallic
glass (BMG) [251,252], and Al65Cu20Fe10Cr5 quasi-crystals [253]. The
addition of TiB2 and Y2O3 resulted in refined grains with random grain
orientation and homogeneously dispersed particles. The high melting
point of Y2O3 and TiB2 limited the diffusion of Y and Ti into the HEA
matrix [168,249]. In the case of Y2O3, serrated grain boundaries were
obtained because of the added particles exerting Zenar pinning pressure
on the grain boundaries duringsolidification [168]. Y2O3 has also been
added to LPBF-fabricated CrCoNi-based HEAs by coating gas-atomized
powder with Y2O3 nanoparticles to avoid altering the powder
morphology and achieve high-quality parts [27,134]. This approach
resulted in finely dispersed Y2O3 particles in the (CrCoNi)96.9
W0.95Al0.65Nb0.47Re0.47Ti0.30C0.24–Y2O3 high-entropy matrix composite
[27]. The intricate microstructure, including the extrinsic particle, grain
boundary strengthening elements enriching the grain boundaries, and
Nb- and Ti-rich carbides (Figs. 24f and g), endowed the alloy with un­
precedented creep resistance (Section 5.1.6).
The lower melting point of BMGs resulted in complete melting dur­
ing the LPBF process, which, depending on the composition of the BMG,
may result in complex phase composition. Adding 5 wt% of
Fe54.5Cr18.4Mn2.0Mo13.9W5.8B3.2C0.9Si1.3 to a CrMnFeCoNi HEA formed
a single FCC phase because of the high solubility of all the elements in
the matrix alloy. Conversely, 20 wt% of Fe43.7Co7.3Cr14.7
Mo12.6C15.5B4.3Y1.9 resulted in the formation of multiple crystalline and
amorphous phases [251,252]. Adding W and diamond to a CrFeCoNi
HEA caused severe lattice distortion as W and C atoms diffused into the
HEA matrix. For CrFeCoNi with 14 wt% added W, a μ phase shell was
formed as unmelted W diffused into the matrix after a heat treatment
step (Fig. 24h) [248].
When extrinsic particles are added to other classes of HEAs, such as
metastable and eutectic HEAs, it may infringe on the initial intention of
that specific class by altering the chemical composition. The addition of
21
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 21. Microstructural features of C-doped HEAs fabricated by LPBF: (a and b) EBSD and (c) APT images of (CrMnFeCoNi)99C1 [29,231]. (d) SEM backscattered
electron images of (CrMnFeCoNi)100–xCx (0.5≤ x ≤1.5) [233]. EBSD image of (e) (NbMoTaW)99.5C0.5 and (f) NbMoTaW. The insets in (e) and (f) show the average
grain size and misorientation angle, respectively. (g) EDS maps of (NbMoTaW)99.5C0.5 [166].
Fig. 22. Microstructural features of N-doped HEAs fabricated by LPBF: EBSD images and grain size distribution of (a) CrFeCoNi and (b) (CrFeCoNi)98.2N1.8 [30]. (c
and d) Matrix phase and ordered nitrogen complexes in CrMnFeCoNi, with the schematic showing the position of the interstitial nitrogen atoms in the matrix lattice.
Modified from ref. [165]. (e) TEM image and EDS line profile of nanosized oxides in a CrMnFeCoNi HEA [238].
22
­
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 23. Elemental distribution of TiC-containing high-entropy matrix composites: EDS maps of as-printed (a) CrMnFeCoNi, (b) CrMnFeCoNi with 2 wt% TiC, and (c)
CrMnFeCoNi with 1 wt% TiC [167,243]. (d) TEM image of Cr36Co32Ni32 with 3 wt% TiC [26].
WC to Ni2.1AlCrFeCo results in the formation of Al4C3, thereby
consuming Al from the matrix HEA and changing the microstructure
from the eutectic FCC–BCC microstructure to an FCC-dominant micro­
structure [254] with inferior tensile performance [32,128]. The addition
of B4C resulted in interstitial carbon remaining in the Fe40Mn20
Co20Cr15Si5 matrix, which prevented the TRIP mechanism during
deformation, significantly reducing the ductility of the composite [227].
Other matrix HEAs where the chemical composition is highly sen­
sitive include dual-phase 3d transition metal HEAs and precipitationstrengthened HEAs. If extrinsic particles are to be added to
precipitation-strengthened HEAs, the added particles could react with
the precipitate-forming elements (i.e., Al and Ti) and thus hamper the
volume fraction of precipitates formed. Moreover, the optimal weight
fraction and size distribution of different extrinsic particles depend on
the matrix HEA and need to be optimized for performance and print­
ability to maximize the potential of LPBF-fabricated high-entropy matrix
composites.
phase, alloying with additional elements (e.g., Al, Ti, Mo, and Si) may
introduce secondary phases. Changing the material system to refractory
elements tends to stabilize a BCC structure, drastically increasing the
hardness and strength of the alloy but decreasing its printability. Adding
non-metallic interstitial elements might result in the formation of
intermetallic compounds. While 3d transition metal, refractory, and
interstitial HEAs typically form a single solid solution phase in their asprinted state, precipitation-strengthened HEAs and high-entropy matrix
composites are designed to inherently contain nanoized precipitates or
extrinsic particles, respectively. In contrast, eutectic HEAs contain two
distinct phases in large proportions. When subjected to sufficiently high
stress, metastable HEAs undergo the TRIP mechanism, transforming the
FCC structure into a more stable crystal structure (either HCP or BCC
phases). As these stress levels can be reached during LPBF, the as-printed
structure typically contains a mixture of the metastable FCC phase and
the more stable crystal structure.
Because of the intrinsic thermal cycling and rapid cooling rate during
LPBF, a high dislocation density is introduced. This dislocation density
yields a hierarchical microstructure with a cellular network in as-printed
3d transition metal HEAs, precipitation-strengthened HEAs, metastable
HEAs, interstitial HEAs, and high-entropy matrix composites. However,
such dislocation structures have not been reported for eutectic and re­
fractory HEAs, which can be attributed to their distinctly different
crystal structures. Depending on the class of HEAs, the dislocation
density may be tuned through compositional design: increasing the
proportion of extrinsic TiC particles in high-entropy matrix composites
increases the dislocation density [167] while for interstitial (CrMnFe­
CoNi)100–xCx, the dislocation density decreases with increasing x [233].
4.8. Summary
Sections 4.1–4.7 discuss the microstructure of as-printed and postprocessed HEAs from the seven classes. The different design strategies
result in starkly different microstructures in terms of the crystal struc­
ture, phase composition, grain size, and dislocation structure, which in
turn impacts the mechanical, physical, and chemical properties, as will
be elaborated upon in the subsequent sections.
The constituent elements play a major role in the formed micro­
structure. Although most 3d transition metal HEAs form a single FCC
23
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 24. Microstructural features of LPBF-fabricated high-entropy matrix composites: (a) SEM image of CrMnFeCoNi containing 5 wt% TiN [244]. The inset shows
the misorientation angle. (b) SEM image of CrMnFeCoNi containing 12 wt% TiN [28]. The inset shows the grain diameter and misorientation angle. (c) TEM images
of CrMnFeCoNi containing 5 wt% TiN revealing a crystalline–amorphous region [245]. Enlargements of regions (d) C in (c) and (e) D in (d). Elemental distribution of
(CrCoNi)96.9W0.95Al0.65Nb0.47Re0.47Ti0.30C0.24–Y2O3 showing EDS maps of: (f) Y and C and (g) W and Re. The graph in (g) shows the APT line scan along the black box
[27]. (h) SEM micrograph of the core–shell structure in CrFeCoNi containing 14 wt% W (red, yellow, and blue denote the FCC phase, unmelted W, and μ phase shell,
respectively) [248].
In both examples, interstitial carbon facilitates the dislocation accu­
mulation. However, in the case of the interstitial HEA, the higher C
concentration in the matrix alloy will promote the formation of carbide
precipitates, which will inhibit the accumulation.
The discussed classes have been established as promising candidates
for LPBF, and only a few LPBF-fabricated HEAs do not belong to a
particular class [255]. Still, multiple HEA classes are yet to be explored
as materials for LPBF, including precious metal HEAs, shape memory
HEAs, and high-entropy brass [13,256]. While 72 elements have been
suggested as potential candidates for HEAs [13], only a fraction of them
have been utilized (Fig. 25). The pool of elements employed in
LPBF-fabricated HEAs is even more shallow, with a staggering focus on
the 3d transition metal elements. This bias is likely exaggerated by the
high cost of preparing high-quality powder feedstock. As the cost of
gas-atomized powder decreases and the accuracy of computational
simulations is enhanced, increased efforts in mapping the uncharted
areas of the periodic table are predicted, which will be necessary to
unlock the full potential of HEAs and expand the limited portfolio of
printable alloys for the LPBF process.
Fig. 25. Elements used in conventionally- and LPBF-fabricated HEAs.
reported for LPBF-fabricated HEAs, including outstanding tensile and
compressive properties, excellent corrosion resistance, and unmatched
high-temperature creep resistance. This section summarizes these
properties, focusing on comparing the classes of LPBF-printed HEAs.
5. Properties of LPBF-fabricated HEAs
Promising mechanical, physical, and chemical properties have been
24
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
5.1. Mechanical properties
the cost of reduced elongation due to the formation of a high density of
precipitates that obstruct dislocation propagation. Eutectic HEAs have
among the highest yield strength of all LPBF-fabricated HEAs, with an
eutectic Ni40Co20Al18Cr10Fe10W2 HEA demonstrating the highest
strength reported to date (~1492 MPa) [32].
The benefit of metastable HEAs is not their yield strength but their
high elongation, with Fe60Co15Ni15Cr10 demonstrating the highest total
elongation of all the LPBF-fabricated HEAs [35,279]. The work hard­
ening offered by the TRIP mechanism increased the ultimate strength of
Fe50Mn30Cr10Co10, (Fe50Mn30Cr10Co10)95Si5, and Fe40Mn20Co20Cr15Si5
HEAs to 250%, 234%, and 207%, respectively, relative to the yield
strength [25,36,226]. The yield strength can effectively be improved
through the incorporation of additional alloying elements [37], extrinsic
particles [227], or interstitial elements [225]. The strengthening effect
of extrinsic particles increases the yield strength of high-entropy matrix
composites at the expense of ductility. For example, increasing the TiC
content from 1 to 3 wt% in CrMnFeCoNi HEAs increased the yield
strength from 748 to 1149 MPa but reduced the total elongation from
29% to 5% [167]. To date, the tensile properties of only a few
LPBF-fabricated refractory HEAs have been reported [177,278]. While
they display impressive strength, their susceptibility to processing de­
fects and the brittle nature of the constituent elements significantly limit
their performance.
The impressive mechanical properties of LPBF-fabricated HEAs arise
from a diverse array of strengthening mechanisms active in these ma­
terials. A deep understanding of these mechanisms is essential to design
high-performance multicomponent materials. This section explores the
tensile and compressive properties as well as the hardness of the HEA
classes. It then delves into the specific strengthening mechanisms and
their contribution to the strength. Finally, other mechanical properties,
including fatigue, creep, and tribological properties, are discussed.
5.1.1. Tensile properties
Fig. 26 compares the yield strength and total elongation of LPBFfabricated HEAs across different classes. There is a wide distribution
of data within the same class due to variations in the alloy composition,
processing conditions, and testing setups. Additionally, the columnar
growth during the LPBF process introduces anisotropy to the printed
alloys, resulting in different properties when the printed part is tested
parallel or normal to the build direction [257,258]. Notwithstanding,
apparent trends can be identified regarding the yield strength and total
elongation of each class.
3d transition metal HEAs, represented by Cr–Mn–Fe–Co–Ni HEAs,
display relatively low yield strength over a wide ductility range due to
limited active strengthening mechanisms. Alloying with additional ele­
ments may enhance the yield strength. For example, adding Si [82] or Al
[191] to a CrFeCoNi HEA increased its yield strength from ~600 to
~701 MPa or ~729 MPa, respectively, because of solid solution
strengthening, dislocation strengthening, and the introduction of a hard
B2 phase (Section 5.1.4). Alternatively, a compositional design that al­
lows for a dual-phase microstructure and sufficiently low stacking fault
energy for TWIP to occur can provide impressive plasticity, as demon­
strated by an Fe60(CrMnCoNi)40 HEA, which consists of both FCC and
BCC phases and has among the highest elongation of LPBF-fabricated
HEAs [259].
The solute elements in interstitial HEAs enhance their strength
compared to that of 3d transition metal HEAs through solid solution
strengthening and the formation of intermetallics [232,233].
Precipitation-strengthened HEAs exhibit significantly different me­
chanical properties before and after the aging step. Before aging, their
yield strength and elongation are similar to those of interstitial HEAs
because of solid solution strengthening and potential secondary phases
introduced by the printing process. After aging, their strength increases
significantly, becoming among the highest for LPBF-fabricated HEAs at
5.1.2. Compressive properties
Fig. 27a illustrates the compressive yield strength plotted against
ductility for LPBF-fabricated HEAs. Compared to the tensile data,
compressive properties are more sensitive to sample size, making it
challenging to compare compressive properties across multiple studies
[282]. Thus, evaluating the mechanical properties by tensile deforma­
tion is preferred, which explains the more limited compressive data.
Additionally, several studies did not report the fracture strain, only that
the fabricated samples did not fracture under a particular strain. With
the insufficient data, comparing the compressive properties across
different classes of HEAs is challenging.
Fig. 27a highlights that HEAs with a BCC structure (i.e., Alcontaining 3d transition metal HEAs and refractory HEAs) possess
high compressive yield strength but low ductility. HEAs with a single
FCC structure, such as 3d transition metal and non-heat-treated pre­
cipitation-strengthened HEAs, demonstrate high ductility but moderate
strength. This difference is due to the close-packed structure facilitating
slipping between the planes. FCC-structured HEAs containing secondary
phases possess strength and ductility between those of pure BCC- and
Fig. 26. Tensile yield strength and ductility of 3d transition metal HEAs [22,84,143,145,147–150,180,186,189,239,238,257,259–270], eutectic HEAs [32,33,128,
129,133,157,205,207,208,271,272–276], precipitation-strengthened HEAs [39–41,173,158–160,277], refractory HEAs [177,278], metastable HEAs [25,35,36,162,
163,226,228,279], interstitial HEAs [29,30,165,179,164,231,232,234,236,280,281], and high-entropy matrix composites [26,28,243,244,248,269].
25
­
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 27. Compressive properties and microhardness of LPBF-fabricated HEAs: (a) Compressive yield strength plotted against the ductility of 3d transition metal HEAs
[42,180,188,194,196,240,283], eutectic HEAs [156,209], a precipitation-strengthened HEA [219], an interstitial HEA [166], refractory HEAs [23,38,166,224,284],
and high-entropy matrix composites [28,251,252]. (b) Microhardness of 3d transition metal HEAs [82,83,103,132,142,148,149,151,183–185,190,194–196,211,251,
264,265,285,286–289], precipitation-strengthened HEAs [39,41,219], refractory HEAs [23,31,137,140,290], eutectic HEAs [207,209,211,272,291,292],
high-entropy matrix composites [105,168,249,251,293], interstitial HEAs [31,236], and metastable HEAs [226]. BMG and BMG* denote Fe54.5Cr18.4Mn2.0
Mo13.9W5.8B3.2C0.9Si1.3 and Fe43.7Co7.3Cr14.7Mo12.6C15.5B4.3Y1.9, respectively.
FCC-structured HEAs. These alloys include heat-treated precipitationstrengthened HEAs and high-entropy matrix composites. While eutectic
HEAs consist of both FCC and BCC phases, the higher fraction of the BCC
phase in Ni2.1AlCrFeCo results in higher compressive yield strength and
lower ductility than Ni3.0AlCrFeCu [156,209].
Unlike the tensile properties, the compressive properties of re­
fractory HEAs have been extensively investigated because these prop­
erties are less influenced by processing defects. These alloys are
characterized by impressive strength, which can be maintained even at
elevated temperatures [221,222]. However, refractory HEAs show
limited ductility, and extensive research has focused on improving it.
Alloying a refractory NbMoTaW HEA with C, thus converting it into an
interstitial HEA, simultaneously enhanced its compressive yield strength
and ductility by 539 MPa and 2.4%, respectively [166]. The enhanced
performance was attributed to the formation of NbC at the grain
boundaries. This formation enhanced the strength by precipitate
strengthening and the ductility by suppressing O segregation, which
would otherwise embrittle the alloy. In another study, a MoTaW HEA
was alloyed with Ti and Ni, resulting in impressive ductility (~15%)
while maintaining a high strength of ~1750 MPa [23]. The MoTaW­
Ni0.5Ti0.5 HEA exhibited refined grains and grain boundary precipitates,
which contributed to strengthening, while the ductility enhancement
was due to a combination of the low stacking fault energy of the grain
boundary precipitates and suppression of processing defects.
microhardness experiences significant variations within the same class
and composition. These variations are because different regions of the
as-printed component experience different thermal histories, resulting
in different texture and hardness values. Cubes of CrMnFeCoNi revealed
that the corner regions of the final layers have higher hardness and a
more inhomogeneous hardness distribution than the central regions
(Fig. 28) [185].
Similar to the case of compressive strength, FCC HEAs show lower
hardness than BCC HEAs as it is easier to initiate slip in the former closepacked structure. As such, 3d transition metal HEAs with a single FCC
5.1.3. Microhardness
The microhardness of LPBF-fabricated HEAs has been extensively
investigated, and Fig. 27b summarizes the recorded Vickers micro­
hardness (HV). Similar to the tensile and compressive properties, the
Fig. 28. Two-dimensional hardness maps of the top, middle, and bottom re­
gions of the centre and corner of an LPBF-fabricated CrMnFeCoNi HEA [185].
26
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
structure, metastable HEAs, and FCC-structured interstitial HEAs pre­
sent the lowest hardness. Among precipitation-strengthened HEAs, asprinted (CrCoNi)94Al3Ti3 [41] and CrFeCoNiCuAl0.3 [219] possessed a
single FCC structure. Co29.5Fe28.0Ni27.5Al8.5Ti6.5 contained a small
fraction of the L21 phase and thus demonstrated high microhardness
[39]. Eutectic and heat-treated precipitation-strengthened HEAs
demonstrate enhanced hardness due to their dual-phase microstructure.
Refractory HEAs typically exhibit high hardness due to the inherent
hardness of the constituent elements. The hardness of high-entropy
matrix composites depends on the type and content of extrinsic parti­
cles added to the composition, and further investigations are required to
better elucidate these effects.
Several strategies have been employed to enhance the hardness of
LPBF-fabricated HEAs through alloy design, printing process optimiza­
tion, and post-printing methods. The strategies that do not require postprinting processes are generally preferred to reduce the cost and time
needed to prepare the final component. Alloy design refers to compo­
sitional optimization. Increasing the Ti content in CrMnFeCoNiTix
enhanced the microhardness [211]. However, solely aiming to maxi­
mize the hardness can be detrimental to the printability of the HEA.
Increasing the Ti content from CrMnFeCoNiTi0.6 to CrMnFeCoNiTi
resulted in the formation of σ phases, which significantly increased the
microhardness (from ~535 to ~973 HV) but resulted in multiple cracks
appearing in the final part. Fe2Ni2AlCr [193,194] demonstrated a higher
fraction of the BCC phase than Fe2.1Ni2.1Al0.9Cr0.9 [83], resulting in
higher hardness but lower printability. This was attributed to the higher
content of BCC-stabilizing Al and the lower content of FCC-stabilizing
Ni.
By tuning the laser power, scan speed, hatch distance, and layer
thickness, the microhardness can be modified correspondingly. For
example, decreasing the scan speed from 800 to 400 mm s–1 enhanced
the microhardness of a refractory VNbMoTaW HEA from ~602.6 to
~719.8 HV, which is attributed to the elimination of pores and grain
refinement by the higher Ev value [137]. When a remelting scan strategy
was used, the microhardness of (CrFeCoNi)98.5Si1.5 increased from ~275
to ~285 HV as the relative density increased [82]. On the other hand,
the microhardness of a CrMnFeCoNi HEA decreased from ~258 to ~222
HV when a remelting scan strategy was used due to the preferential
evaporation of Mn [294]. Alternatively, different approaches can be
employed to affect the printing process. Reactive N2 gas was used to
fabricate an interstitial Cr2.5Ni2TiFeCoW0.5 HEA, resulting in the for­
mation of TiN and increased hardness compared to when a non-reactive
argon gas was used (~436.7 HV) [31].
The effect of annealing on microhardness has been extensively
studied, with varying effects on the hardness. One study reported a
decrease in the microhardness as annealing reduced the residual stress
and eliminated the dislocation substructure induced during the LPBF
process. Consequently, the microhardness of CrFeCoNi [265] and
AlFeCoNiCu [196] decreased with increasing annealing temperature
and time. While the microhardness of Fe2Ni2AlCr and
Fe2.1Ni2.1Al0.9Cr0.9 HEAs also decreased after annealing, it was instead
attributed to the increasing fraction of the softer FCC phase [83,193,
194]. However, post-process annealing might result in the formation of
secondary phases, such as in the case of precipitation-strengthened
HEAs, thus increasing the microhardness. A (CrCoNi)94Al3Ti3 HEA
showed a significant increase in microhardness after annealing at
~800–900 ◦ C due to the formation of the hard but brittle σ phase [41].
Annealing at higher temperatures (1000–1100 ◦ C) formed a
dislocation-free single FCC phase, thus showing decreased hardness
compared to the as-printed HEA.
Annealing carbon-containing interstitial HEAs resulted in the for­
mation
of
Cr23C6
carbides
[233,236].
Similar
to
precipitation-strengthened HEAs, annealing a CrFeCoNiC0.05 HEA for
0.5 h at 800 ◦ C resulted in the highest hardness among annealing times
of 0–8 h. Extending the annealing time decreased the hardness because
of reduced residual stress and dislocation density [236]. Increasing the
annealing temperature above 650 ◦ C for (CrMnFeCoNi)100–xCx
decreased the hardness because of dislocation recovery, although
increasing the C content decreased this tendency [233]. High-pressure
torsion is another post-printing process used to enhance the hardness
[295]. The CrFeCoNi HEA was subjected to high-pressure torsion
(6 GPa, 0.5–8 turns) to significantly decrease the grain size, thus
increasing the hardness from 260 to 400–510 HV [295].
5.1.4. Strengthening mechanisms
Fig. 29 shows a schematic representation of the strengthening
mechanisms active in LPBF-fabricated HEAs. Some of these mechanisms
are inherent to specific chemical composition while others are inherent
to the LPBF process. Multiple strengthening mechanisms can be active at
different length scales within the same HEA, enabling a strong syner­
gistic effect.
The tensile yield strength of an alloy is described according to [147]
σ y = σm + σGb + σ ρ + σ or + σ coh ,
(4)
where σ m , σgb , σρ , σ or , and σcoh are the contributions from matrix
strengthening, grain boundary strengthening, dislocation strengthening,
Orowan strengthening, and precipitates with a coherent interface to the
matrix, respectively. Alternatively, the mean root square of σρ , σgb , σor ,
and σcoh can be considered to account for their interactions under an
external force [160,238],
√̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
(5)
σ y = σm + σgb + σ ρ + σor + σ coh .
The σm component combines the contributions from solid solution
and intrinsic-frictional strengthening [145]. Solid solution strength­
ening stems from mixing multiple elements with different atomic radii,
thereby providing lattice distortions, and thus, the contribution to the
overall strength varies with the chemical composition [13]. Defining the
solute and solvent atoms in HEAs can be challenging because of the use
of multiple elements in near-equiatomic ratios. In the case where such
distinctions
can
be
made
(e.g.,
interstitial
and
precipitation-strengthened HEAs), the solid solution strengthening σss
can be estimated by [41,82,250,251]
Fig. 29. Schematic of the strengthening mechanisms reported in LPBFfabricated HEAs.
27
A. Jarlöv et al.
σ ss = M
√̅̅̅
Gε3/2 c
,
700
Materials Science & Engineering R 161 (2024) 100834
(6)
γ
2b
σ coh = 0.81M APB
where G and c are the shear modulus and molar ratio of the solute atom,
respectively, while M is a constant (equal to 3.06 for FCC metals and
2.75 for BCC metals) [274]. The mismatch parameter ε is defined as
⃒
⃒
⃒
⃒
εG
ε = ⃒⃒
− 3εa ⃒⃒,
(7)
1 + 0.5εG
(13)
where γAPB represents the anti-phase boundary energy. Another type of
coherent precipitate is the spherical ordered BCC particles encountered
in the BCC lamella of eutectic HEAs [274].
The strengthening mechanisms mentioned above have been used to
predict the yield strength of HEAs. While the TRIP mechanism also
contributes to increased strength through work hardening (Fig. 29), it
does so during plastic deformation and is thus only active once plastic
deformation is initiated. The stacking fault energy determines whether
an HEA will deform by the TRIP mechanism. As the stacking fault energy
decreases, the dislocation slip, twinning-induced plasticity (TWIP), or
TRIP mechanisms are facilitated [109,297]. The TWIP mechanism
governs the deformation of alloys with stacking fault energy in the range
of 18–45 mJ m–2 [298]. When the stacking fault energy is below
18 mJ m–2, the TRIP mechanism will instead govern the deformation, as
described for the metastable HEAs [36,298]. Twins can act as obstacles
for dislocations, similar to grain boundaries, and can thus provide
strengthening through the dynamic Hall–Petch effect [299]. The TWIP
mechanism is also an underlying cause for the anisotropy observed in
LPBF-printed parts as it is heavily dependent on the grain orientation,
resulting in diagonally printed parts experiencing a higher twinning
tendency than horizontally and vertically printed ones [257].
Fig. 30 shows the contribution of different strengthening mecha­
nisms to the overall tensile yield strength of LPBF-fabricated 3d transi­
tion metal HEAs, interstitial HEAs, precipitation-strengthened HEAs,
eutectic HEAs, metastable HEAs, and high-entropy matrix composites.
Because of the similar atomic radii of the constituent elements, 3d
transition metal HEAs have limited σ ss [282], and the strength is mainly
contributed by σρ and σ gb . The high σgb contribution for CrCoNi HEAs
was shown to be due to the dislocation cell boundaries acting as
high-angle grain boundaries [145], while the presence of oxygen during
the printing process resulted in the formation of oxides in CrMnFeCoNi,
which contributes to σ or [240]. Interstitial HEAs demonstrate a higher
yield strength than 3d transition metal HEAs due to the interstitial ele­
ments, dislocation density, and formation of M23C6-type carbides, which
where εG and εa refer to the elastic and atomic size mismatch, defined as
G− 1 ∂G/∂c and a− 1 ∂a/∂c, respectively (a refers to the lattice parameter).
The refined grains observed in LPBF-fabricated parts enhance the
strength through grain boundary strengthening. The σ gb contribution is
commonly calculated using the classic Hall–Petch relationship [145,
239,296],
/√̅̅̅
d,
(8)
σ gb = ks
where ks and d refer to the Hall–Petch coefficient and grain size,
respectively. In some studies, the average size of the dislocation cells
was used, thus assuming that the dislocation cells can act as high-angle
grain boundaries [145,249]. However, others reported that this
approach overestimates the yield strength [147,225]. Using interstitial
elements and different scan strategies may result in a bimodal grain size
distribution, with fine and coarse grain sizes (dfine and dcoarse , respec­
tively). In such cases, the effective grain size deff is estimated by [29,30,
231]
(
)− 1
Vfine Vcoarse
deff =
+
,
(9)
dfine dcoarse
where Vfine and Vcoarse refer to the volume fraction of the fine and coarse
grains, respectively.
The high dislocation density in LPBF-fabricated HEAs results in
higher σ ρ than that of conventionally manufactured HEAs, as estimated
by the Taylor hardening law [39,147],
σ ρ = MαGbρ1/2 ,
√̅̅̅̅̅̅̅̅̅̅
3πvp
,
8
(10)
where α is a constant, b is the Burgers vector, and ρ is the dislocation
density. Multiple methods exist for evaluating the dislocation density,
resulting in slight deviations for the same alloy.
The σ or and σ coh contributions originate from the precipitation of
secondary phases. Incoherent precipitates contribute to σ or according to
[150,240,257]
(
)( ) (√̅̅̅̅̅̅̅̅ )
2/3dp
0.4M
Gb
ln
σ or = √̅̅̅̅̅̅̅̅̅̅̅
,
(11)
L
b
π 1− v
where v, dp , and L refer to the Poisson’s ratio, inter-particle spacing, and
mean particle diameter, respectively. Examples of incoherent pre­
cipitates include the σ phase [41], oxides [238,239], carbides [231–233,
280], and certain extrinsic particles [248,249]. However, if the inco­
herent precipitates are smaller than a critical size, the dislocations will
slice through the precipitates, resulting in a softening behavior. The
strengthening contribution from the incoherent L21 precipitate in
precipitation-strengthened HEAs is given by a modified version of the
Orowan equation [158,220]:
σ L21 =
0.13Gb
r
ln ,
L
b
(12)
where r is the radius of the incoherent precipitate. Coherent precipitates
have a crystal structure similar to the matrix phase and a low lattice
mismatch. A good example is the L12 precipitates encountered in
precipitation-strengthened HEAs, which contribute to σcoh according to
[41,158,220]
Fig. 30. Yield strength and calculated contribution of different strengthening
mechanisms in LPBF-fabricated 3d transition metal HEAs [145,165,150,240],
interstitial HEAs [165,231,232], precipitation-strengthened HEAs [39,41,220],
eutectic HEAs [32,128,274], metastable HEAs [35,225], and high-entropy
matrix composites [26,167,243,249,248].
28
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
affect σ ss , σρ , and σor , respectively [165,231,280]. Although a higher C
content decreases the dislocation density and increases the grain size,
thus decreasing σρ and σ gb , the increased σ or contribution from the
formed carbides results in an overall increase in the yield strength [232,
233]. The increase in the grain size was attributed to enhanced diffusion
of the constituent elements as the carbon content increased, thus facil­
itating grain growth.
The Al and Ti atoms in precipitation-strengthened HEAs provide σ ss
due to their sizeable atomic radii compared to those of the other con­
stituent elements, while the formation of the incoherent L21 phase
provides σ or before heat treatment [39,173]. After the aging step,
coherent L12 results in enhanced strength due to increased σcoh . The
aging step must be optimized to allow the precipitates to form without
removing the dislocations introduced by the printing process, as this
would reduce the σ ρ contribution [39]. The ultra-fine nano-lamellar
spacing of eutectic HEAs contributes significantly to σgb , resulting in
their high strength [32,128,157].
While eutectic HEAs have been increasingly investigated for LPBF
applications, a rigorous understanding of the strengthening mechanisms
in LPBF-fabricated eutectic HEAs has not been achieved. As an example,
the σm contribution of conventionally manufactured Al0.3CrFeCoNi is
commonly used, and the role of σ coh is still unclear [128,274]. The main
strengthening mechanisms of metastable HEAs (i.e., TWIP and TRIP) are
only available once plastic deformation is initiated. As such, metastable
HEAs can only rely on σgb and σρ [35,225], resulting in low yield
strength. Finally, the high-entropy matrix composites exhibit high σor
from the extrinsic particles. Additionally, the most commonly added
particle, TiC, results in C atoms dissolving in the matrix phase, thus
contributing to σss [167].
phases in eutectic HEAs and precipitation-rich regions in
precipitation-strengthened HEAs) which can be architected to optimize
the heterogenous deformation-induced strengthening and strain hard­
ening. A hetero-boundary affected region exists in the LPBF-fabricated
samples, proposed based on the dislocation pile-up theory [302],
which must be used to optimize the size of the different domains.
Some conventionally fabricated HEAs have demonstrated the po­
tential of combining features that enhance both strength and ductility,
including Fe-rich maraging HEAs where the precipitates can undergo
phase transformation during deformation to enhance the ductility [303,
304], eutectic HEAs with a dual FCC-phase structure where both phases
can accommodate high plastic deformation [305], and refractory HEAs
with high twinnability [306]. By incorporating design criteria to ensure
high printability, novel LPBF-fabricated HEAs that surpass current
strength–ductility synergy standards can be realized.
5.1.6. Other mechanical properties
Although most studies on LPBF-fabricated HEAs focus on tensile
properties, compressive properties, and microhardness, recent studies
have begun evaluating other mechanical properties, including fatigue,
creep, fracture toughness, and tribological properties. These efforts must
be extended in the future to prove that LPBF-fabricated HEAs can meet
the stringent requirements of modern industry.
Poor fatigue performance may result in devastating failures, so
strategies that improve fatigue resistance warrant investigation [307].
Because of the high dislocation density of as-printed HEAs, cyclic soft­
ening occurred after only ten cycles in as-printed CrMnFeCoNi, resulting
in a low fatigue life of ~103 cycles [146,180]. Improving the surface
finish through machining enhanced the fatigue life by ~20% by elimi­
nating processing defects near the surface. While the primary defor­
mation mechanism in CrMnFeCoNi during cyclic deformation was
dislocation slip, deformation twinning was observed in a CrFeCoNi HEA
because of the large grain size [241], which enhanced the fatigue
resistance.
Conversely,
metastable
[37,110]
and
precipitation-strengthened [40] HEAs present good fatigue life in the
as-printed state as the formed HCP regions and precipitates can halt
crack propagation, respectively.
As-printed Fe40Mn20Co20Cr15Si5 exhibited a fatigue life of ~107 cy­
cles and an endurance limit of 325 MPa for a similar stress amplitude as
that of the CrMnFeCoNi HEA [37]. The TRIP mechanism reduces the
number of potential stress concentration sites from processing defects
while also causing crack branching along slip bands. A
precipitation-strengthened (FeCoNi)86Al7Ti7 HEA demonstrated a syn­
ergistic effect between the L12 and L21 precipitates, where the
nano-sized L12 precipitates prevented the expansion of slip bands, while
the coarser L21 precipitates halted the slip band and deflected the crack
[40]. HEAs with similar microstructural features to hinder crack prop­
agation, such as precipitation-containing interstitial HEAs, eutectic
HEAs, and high-entropy matrix composites, may also demonstrate high
fatigue resistance and should be explored. Moreover, while microvoids
cause printed parts to have inferior fatigue properties compared to
conventionally fabricated ones, strategies to obtain void-free parts have
demonstrated that the LPBF technology can yield exceptional fatigue
properties, and strategies to obtain such parts must be pursued [308].
Typically, HEAs are credited with high creep resistance due to
sluggish diffusion [104]. However, as the cellular dislocation network
formed during the LPBF process can accelerate diffusion, it is unclear if
this claim applies to printed HEAs [39]. Nanoindentation creep studies
on a CrMnFeCoNi HEA using a Berkovich indenter revealed a high-stress
component, 16.67–27.03 for a load of 5–50 mN, similar to conven­
tionally manufactured CrMnFeCoNi with the same grain size [183]. The
classic creep theory could not explain the high-stress component, and it
was theorized that the migration of dislocations controlled the creep.
At elevated temperatures, the creep resistance becomes crucial. Since
LPBF-fabricated HEAs are envisioned as materials for such temperature
ranges, alloy design must consider creep properties. The creep resistance
5.1.5. Designing LPBF-fabricated HEAs with excellent strength–ductility
synergy
Given the longstanding quest to push the strength–ductility synergy
further, a few remarks on designing HEAs with excellent strength and
ductility for LPBF will be provided. As evident from Fig. 26, the eutectic
and precipitation-strengthened classes of HEAs demonstrate the highest
strength while the metastable HEAs possess the highest ductility.
Further extending the strength–ductility synergy will likely involve
combining the features from these classes by using a broader palette of
constituent elements.
Regarding high strength, the eutectic and precipitation-strengthened
HEAs obtain their high strength from σ gb and σcoh , respectively (Fig. 30).
However, the entire hierarchical microstructure obtained from the LPBF
process contributes to the outstanding strength, as the classes demon­
strate enhanced mechanical properties when printed compared to when
they are fabricated by conventional techniques [32,39]. The heteroge­
neous microstructure inherent to the LPBF process will result in heter­
ogenous deformation-induced strengthening [300], which can be
characterized by the back stress [32]. By enhancing the contributions
from other strengthening mechanisms, such as σ ss and σ or , an even
stronger alloy can be obtained. Examples include alloying with Mo, W,
and Re [27,86] to enhance σ ss and introducing interstitial elements,
which would contribute to both σ ss and σor . Interstitial elements show
the potential to enhance the strength without compromising ductility,
particularly for refractory HEAs [301], and can be introduced by per­
forming the print job in a reactive gas atmosphere [31,165].
Regarding high ductility, it is necessary that extensive work hard­
ening occurs during plastic deformation. For the metastable HEAs, this
typically occurs in the form of TWIP and TRIP because of a low stacking
fault energy. Alternatively, lowering the stacking fault energy suffi­
ciently to allow for extensive dislocation activity can enhance the workhardening efficiency [110]. Similar to the strength, the inherent het­
erogeneous
microstructure
will
result
in
heterogenous
deformation-induced strain hardening [300]. The multi-element nature
of HEAs introduces additional hard and soft domains (e.g., FCC and BCC
29
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
at elevated temperatures of LPBF-fabricated CrMnFeCoNi doped with O
[125] and C [309] was examined and showed a lower creep rate than
conventionally manufactured CrMnFeCoNi (Fig. 31a) [310]. A (CrCo­
Ni)96.9W0.95Al0.65Nb0.47Re0.47Ti0.30C0.24–Y2O3 high-entropy matrix
composite fabricated by LPBF demonstrated exceptional creep rupture
life compared to other LPBF-fabricated superalloys at 1093 ◦ C (Fig. 31b)
[27]. The outstanding creep resistance of the HEA was attributed to
multiple types of elemental heterogeneity, including extrinsic particles,
the formation of carbides, and the segregation of Cr, W, and Re to the
grain boundaries. Such heterogeneity, exaggerated in HEAs due to their
complex composition, make these materials promising for high creep
resistance.
One major advantage of HEAs has been their outstanding fracture
toughness, particularly at cryogenic temperatures [11,311]. However,
limited studies have been conducted on the fracture toughness of
LPBF-fabricated HEAs. LPBF-fabricated CrCoNi maintained a respect­
able fracture toughness at cryogenic temperatures, while the yield
strength increased compared to that measured at room temperature
[312]. LPBF-fabricated CrFeCoNiAl0.5 showed impressive fracture
toughness at room temperature compared to other HEAs due to the
honeycomb-like B2 network obstructing the dislocation movement
before uniform plastic deformation was initiated (Fig. 32a) [191].
However, LPBF-fabricated parts generally show lower fracture tough­
ness than their conventionally fabricated counterparts because of the
resulting texture inhibiting the toughening mechanisms, the presence of
processing defects, and oxygen pickup. Additional studies on process
optimization and scan strategies to induce a more favorable grain
texture, minimize processing defects, and reduce oxygen uptake are
urgently needed to enhance fracture toughness.
The tribological properties of LPBF-fabricated HEAs, such as the
friction coefficient and wear rate, have only been briefly studied.
Microhardness is often used to estimate the wear rate and provides
guidelines for developing wear-resistant LPBF-fabricated HEAs (Section
5.1.2.) [168,314]. LPBF-fabricated AlFeCoNiCu showed a lower friction
coefficient and mass loss than spark plasma–sintered samples. While
higher Ev improved the relative density and reduced the friction coef­
ficient, lower mass loss was achieved for lower Ev because of the
development of a more favorable grain texture and lower Young’s
modulus (Fig. 32b) [313]. Dry-sliding of an LPBF-printed eutectic
Ni2.1AlCrFeCo HEA at different temperatures revealed that the wear
mechanism changed from adhesive wear at room temperature to adhe­
sive and oxidative wear at 500 ◦ C and oxidative wear at 700 ◦ C, thus
explaining the lower wear rate at higher temperatures [273]. The wear
resistance could be improved by alloying with Ti [315,316] or adding
TiN particles [28,317] because of grain boundary and precipitate
strengthening in the former case, and grain boundary and Orowan
strengthening in the latter. As refractory HEAs demonstrate among the
highest hardness, they are predicted to have excellent tribological
properties if their processability can be improved.
As evident from the above discussion, fatigue, creep, fracture
toughness, and tribological properties are only evaluated in a few classes
of LPBF-fabricated HEAs. As the field continues to grow, more efforts to
map these and other properties for the remaining classes of HEAs are
necessary.
5.2. Physical and chemical properties
While most research on LPBF-fabricated HEAs has focused on me­
chanical properties, the importance of evaluating their physical and
chemical properties is increasingly recognized. Recent studies have
explored their resistance to environmental degradation, including
corrosion and hydrogen embrittlement. Additionally, the hightemperature oxidation and magnetic properties of LPBF-fabricated
HEAs have been investigated. As the field matures, more studies tar­
geting functional properties are predicted to emerge.
5.2.1. Corrosion properties
Corrosion impacts all materials where an electron-transferring me­
dium (electrolyte) connects a more noble region (cathode) with a less
noble one (anode). While conventional corrosion produces a high cost to
society [318], it becomes exceptionally demanding in harsh environ­
ments such as marine applications, fuel cells, and syngas pipelines [319,
320]. To address these challenges, metallurgists have developed
corrosion-resistant alloys capable of withstanding these environments
[321,322]. HEAs have demonstrated impressive corrosion resistance,
even surpassing conventional alloys containing noble metals [37,150,
323].
Key factors for alloy design that affect corrosion are the stability of
the formed passive film, the microstructure of the HEA, and the exis­
tence of processing defects, while external factors such as the operating
temperature and pH also play a major role [324,325]. A stable passive
film can prevent further corrosion reactions once formed, significantly
enhancing the corrosion resistance. HEAs composed of valve metals (i.e.,
Ti, Zr, Ta, Nb, etc.) can form stable passive films even in acidic envi­
ronments [326,327]. For HEAs consisting of 3d transition metals, pre­
vious studies have demonstrated that a higher ratio of Cr, Co, and Ni
over Mn and Fe enhanced the corrosion resistance [249,328]. Regarding
the microstructure, refining the grain size and eliminating elemental
segregation, both impacting the passive film, will enhance the corrosion
resistance [325].
LPBF-fabricated CrMnFeCoNi has a higher ratio of Cr, Co, and Ni
over Mn and Fe than as-cast CrMnFeCoNi, demonstrating that the
former has a stronger passive film, potentially due to preferential Mn
evaporation during LPBF [328]. The oxide layer of a CrFeNi HEA
Fig. 31. Creep response of LPBF-fabricated HEAs: (a) Double logarithmic plot of minimum creep rate against stress for conventionally fabricated CrMnFeCoNi and
LPBF-fabricated O- and C-doped CrMnFeCoNi, referred to as O-HEA and C-HEA, respectively [309]. (b) Scatter plot of creep rupture life of LPBF-fabricated su­
peralloys at 1093 ◦ C [27].
30
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 32. Fracture toughness and tribological properties of LPBF-fabricated HEAs: (a) Fracture toughness as a function of the yield strength for various alloys [191].
(b) Mass loss after wear test for LPBF-fabricated and spark plasma–sintered AlFeCoNiCu HEAs. The insets show the EBSD maps for AlFeCoNiCu printed using
different Ev. Modified from [313].
contained a high Cr2O3 content as the Cr-rich cellular boundaries could
facilitate the diffusion of Cr to the surface [150]. The rapid cooling rate
of LPBF helps reduce the grain size and suppress elemental segregation.
However, the tendency to introduce processing defects such as pores,
residual stress, and cracks adversely affects corrosion resistance [324].
Cracks and pores will affect the stability of the passive film by allowing
aggressive ions to accumulate, thereby exaggerating pitting corrosion,
while residual stress and stress fields from subsurface pores can act as
initiation points for localized corrosion [329].
Fig. 33a summarizes the corrosion properties of LPBF-fabricated
HEAs tested in a simulated seawater environment (i.e., 3.5 wt% NaCl).
The corrosion potential Ecorr and corrosion current icorr are indicators of
corrosion resistance, where high Ecorr and low icorr indicate excellent
corrosion resistance. The icorr values of LPBF-fabricated HEAs span
several orders of magnitude because of differences in the constituent
elements and printing quality. Corrosion resistance is highly dependent
on the structure and composition of the passive oxide layer formed on
the surface. The refractory NbMoTaW HEA shows the best corrosion
resistance [330], attributed to the Nb and Ta elements forming passive
Nb2O5 and Ta2O5 oxides, respectively, that protect the alloy from further
corrosion [327]. Adding such valve elements has also improved the
corrosion resistance of 3d transition metal HEAs [331], although
Fig. 33. Corrosion of LPBF-fabricated HEAs: (a) Logarithm of icorr plotted against Ecorr for LPBF-fabricated HEAs in a 3.5 wt% NaCl electrolyte [44,47,103,150,249,
316,328,330–333]. The temperature next to the alloy composition denotes the annealing temperature. Surface corrosion morphology of LPBF-fabricated CrMnFe­
CoNi (b) parallel and (c) perpendicular to the build direction [332]. (d) SEM micrograph of a corroded as-built Fe38.5Mn20Co20Cr15Si5Cu1.5 HEA. The inset shows the
EDS map of Cu [37].
31
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
excessive addition of such elements may result in intermetallic phases,
which are prone to pitting corrosion [316].
Processing defects such as pores, microcracks, and elemental segre­
gation can reduce the corrosion resistance of LPBF-fabricated HEAs
(Figs. 33b–d) [37,200,332]. While the Ecorr value of LPBF-fabricated
CrMnFeCoNi was lower than that of the as-cast HEA, selective pitting
corrosion occurred at the processing defects, significantly reducing the
corrosion resistance [332]. However, if the printed part maintains high
quality, and defects are avoided, single-phase LPBF-fabricated HEAs can
exhibit higher corrosion resistance than conventionally manufactured
parts. The rapid cooling rate in LPBF results in improved corrosion
resistance due to homogenized elemental distribution and decreased
grain size [328]. A smaller volume fraction of secondary precipitates
was formed in (CoNi)1.5CrFeTi0.5Mo0.1 fabricated by LPBF, resulting in
better corrosion resistance than the same HEA fabricated using electron
beam melting [202].
Dual-phase HEAs may be susceptible to selective pitting corrosion
because of the varying contributions of the corrosion-resistant elements
in the different phases. In such cases, a heat treatment step is required to
homogenize the distribution of the elements. Heat treatment resulted in
a trade-off in the corrosion resistance and strength for LPBF-fabricated
(CrMnFeCoNi)91Al9 [47]. A heat treatment at 850 ◦ C resulted in the
highest strength due to a high fraction of the B2 phase rich in Al and Ni,
while a heat treatment at 1050 ◦ C reduced the elemental inhomogeneity
and enhanced the corrosion resistance. Regarding the high-entropy
matrix composites, the corrosion resistance depends on the added
extrinsic particles. Adding 5 wt% bulk metallic glass decreased the
corrosion resistance of CrMnFeCoNi [251] while adding 1 wt% TiB2 to
CrFeCoNi increased it because of a higher ratio of Cr, Co, and Ni over Fe
in the passive film [249]. Further investigations are required to deter­
mine the effect of other extrinsic particles on corrosion resistance.
Apart from being tested in simulated seawater (3.5 wt% NaCl), LPBFfabricated HEAs have been tested in more corrosive electrolytes. A series
of Al–Ti–V–Fe–Co–Ni–Zr HEAs were prepared in ref. [44]. While the
AlFeNiCoZrV0.9Sm0.1 HEA demonstrated the highest corrosion resis­
tance in 3.5 wt% NaCl, TiAlFeNiCoV0.9Sm0.1 and AlFeNiCoV0.9Sm0.1
prepared by LPBF were tested in a simulated syngas environment at an
elevated temperature (500 ◦ C). Although the TiAlFeNiCoV0.9Sm0.1 HEA
was more noble (higher Ecorr), the AlFeNiCoV0.9Sm0.1 HEA showed
lower icorr and greater capacity, which was attributed to the hydroge­
nation reaction of Ti [319]. Because of potential elemental segregation
to the grain and cell boundaries induced by the LPBF process, a heat
treatment step might be necessary to homogenize the elemental distri­
bution and improve the corrosion resistance. Good corrosion resistance
was achieved in LPBF-fabricated CrMnFeCoNi after a heat-treatment
step at 800 ◦ C for 2 h because of the elimination of Mn segregation at
the cellular boundaries [334]. However, the formation of secondary
phases during a heat treatment step may instead impair the pitting
corrosion resistance [47], which must be considered when designing
interstitial and precipitation-strengthened HEAs.
The design of corrosion-resistant LPBF-fabricated HEAs can benefit
from evaluation indexes that can be used to create datasets for compu­
tational frameworks and machine learning algorithms. One such index is
the percolation theory proposed by Sieradzky and Newman to identify
the content of noble elements required to form a stable passive oxide
layer [335]. Utilizing this theory, the content of Ta and W required to
prepare corrosion-resistant CrFeNi-based HEAs was determined [336].
Another index is the Pilling–Bedworth ratio, defined as the volume of
metal oxide over the volume of consumed metal [337]. An increasing
Pilling–Bedworth ratio indicates a buildup of compressive stress inside
the film, which might cause delamination [292]. The Pilling–Bedworth
ratio, in combination with ab initio calculations, has been used to
accelerate the design of corrosion-resistant HEAs [338]. Incorporating
printability information allows for the development of frameworks
specifically for corrosion-resistant LPBF-fabricated HEAs.
5.2.2. Hydrogen embrittlement
Hydrogen embrittlement, i.e., the simultaneous loss of strength and
ductility due to hydrogen absorption, is another type of environmental
damage that occurs to alloys in a hydrogen-rich environment [339]. The
exposure of an alloy to hydrogen can be either ex situ (testing the
sensitivity of the alloy to internal hydrogen) [263,340] or in situ (testing
the sensitivity of the alloy to external hydrogen) [341,342]. In situ
exposure is closer to actual service conditions and is generally more
harmful [263,340].
During ex situ exposure, hydrogen diffuses through the lattice ac­
cording to Fick’s law, and the hydrogen-affected zone is generally
shallow; an exposure of 6 h may result in a hydrogen-affected zone with
a depth of ~2.8 µm [340]. The absorbed hydrogen reduces the stacking
fault energy of LPBF-fabricated CrMnFeCoNi, thus increasing the frac­
tion of deformation twins from 4.3% to 18.6% [266]. This mechanism
enables hydrogen-charged CrMnFeCoNi to have a similar or even higher
work hardening rate than the uncharged HEA. However, during in situ
exposure, the concentration of hydrogen CH continuously increases,
allowing new hydrogen atoms to be absorbed through freshly opened
cracks and diffuse along grain boundaries by stress-driven diffusion
(Fig. 34). When CH exceeds a critical value, hydrogen-assisted cracks
initiate, causing the alloy to fail.
Generally, conventionally manufactured HEAs have demonstrated
good resistance to hydrogen embrittlement [343]. However, the cellular
network of LPBF-fabricated HEAs facilitates hydrogen uptake, and a
heat treatment step is required to remove the cellular network and
improve the resistance to hydrogen embrittlement [263,342]. In
CrMnFeCoNi, the cellular network is accompanied by a high dislocation
density and Mn segregation, which act as hydrogen trapping sites and
promote intergranular cracking during in situ exposure [342]. A heat
treatment step at 900 ◦ C for 1 h reduces the dislocation density and
eliminates the elemental segregation, thus suppressing the hydrogen
embrittlement effect.
With the hydrogen economy emerging as a response to the envi­
ronmental stress caused by modern industry, it is necessary to develop
high-performance alloys with increased resistance to hydrogen embrit­
tlement. As the LPBF process can negatively influence this parameter
because of the cellular dislocation network and increased density of
grain boundaries, it is necessary to enhance the hydrogen embrittlement
resistance by other means. By leveraging the compositional design, the
resistance to hydrogen embrittlement can be enhanced by increasing the
grain boundary cohesion to inhibit hydrogen diffusion along grain
boundaries or by decreasing the stacking fault energy to allow for TWIP
during deformation [344]. The grain boundary cohesion may be
enhanced by adding grain boundary strengthening elements (e.g., B and
C) while the addition of Al, Si, Mn, and Cr can decrease the stacking fault
energy. The effect of adding such elements on the resistance to hydrogen
embrittlement of LPBF-fabricated HEAs should be carefully explored.
5.2.3. Other physical and chemical properties
Oxidation resistance is crucial for alloys used at high temperatures.
LPBF-fabricated HEAs, including 3d transition metal HEAs [345,346],
eutectic HEAs [292], refractory HEAs [169], and high-entropy matrix
composites [134,169], have been evaluated for this property. Achieving
good oxidation resistance requires the formation of stable oxides that do
not delaminate. Tuning the composition or adding extrinsic particles are
effective strategies for improving oxidation resistance. For example,
during oxidation at 1000 ◦ C, the Mn- and Cr-rich oxide film on
LPBF-fabricated CrFeCoNi tended to delaminate, causing weight loss
[345]. Adding Al through mechanical alloying can prevent this by
forming an underlying Al2O3 layer, although excessive Al increases
weight gain during oxidation. Similarly, adding 4 wt% TiC to VNbMo­
TaW forms a protective TiO2 and Ti2Nb10O29 film, preventing further
oxidation [169].
Processing defects from LPBF also impact oxidation resistance. In
CrMnFeCoNi, residual melt pool boundaries facilitated oxidation while
32
­
­
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 34. Schematic illustration showing the difference in hydrogen permeation between the ex situ and in situ hydrogen exposure [340].
annealing improved the resistance by homogenizing the microstructure
[346]. Pores in Ni2.1AlCrFeCo act as nucleation sites for oxide formation,
thus impairing the oxidation resistance [292]. Oxidation kinetics for
both alloys are diffusion-driven and follow the parabolic law. These
preliminary studies must be extended for LPBF-fabricated HEAs to be
considered for high-temperature applications, such as rocket engines,
turbine blades, and nuclear reactors. Moreover, the multi-element na­
ture of HEAs yields a complex mixture of different oxides distinct from
those formed on conventional alloys, thus necessitating fundamental
research on the effect of alloying elements, mechanism of oxide for­
mation, and rate of internal oxidation to advance the field. The
compositional design may leverage CALPHAD to promote the formation
of stable oxides during the intended service temperature range through
the addition of Al, Si, Ti, and Cr.
Additive manufacturing of soft magnetic HEAs holds high potential
as the geometric design freedom allows for intricate components to be
fabricated while the compositional design freedom may break the
compromise between magnetic and mechanical properties. However,
the most adopted additive manufacturing technique for soft magnets is
directed energy deposition for its ability to screen multiple alloys rapidly
[347]. To the best of the authors’ knowledge, only the Co47.5Fe28.5
Ni19Si3.4Al1.6 [42] and AlFeCoNiCr0.75Cu0.5 [348] among all soft mag­
netic HEAs have been fabricated by LPBF and had their magnetic
properties evaluated.
For the Co47.5Fe28.5Ni19Si3.4Al1.6 HEA, the scan speed significantly
influenced the saturation magnetization Ms and coercivity Hc while the
laser power had a negligible effect [42]. LPBF-fabricated Co47.5Fe28.5
Ni19Si3.4Al1.6 demonstrated lower Hc than as-cast samples (118.3 A m–1
compared to 1158.37 A m–1), which was attributed to the rapid cooling
rate of LPBF eliminating elemental segregation. Moreover, the
LPBF-fabricated alloy demonstrated higher compression strain than
materials with similar Hc, although the compression yield strain was still
low compared to that of other LPBF-fabricated HEAs (Fig. 27a). The Ms
value of the AlFeCoNiCr0.75Cu0.5 HEA increased from 63.0 to 65.3 Am2
kg–1 with decreasing scan speed because of a higher degree of spinodal
decomposition [348]. While numerous conventionally fabricated mag­
netic HEAs exist, their composition must be further optimized for the
LPBF process to ensure good printability. For example, Cu is a typical
element used [199,349], but it is challenging to fabricate because of
poor laser absorption and requires further compositional optimization
[350]. Additionally, ab initio calculations could guide alloy design by
elucidating the interaction between the chemical composition and
magnetic properties, such as the Curie temperature, magnetic polari­
zation, and magnetic moment.
As the field advances, additional efforts are required to explore the
oxidation and magnetic properties of more alloys. Oxidation resistance
is essential for components designed for service at elevated tempera­
tures, which is a targeted environment for refractory HEAs,
precipitation-strengthened HEAs, and high-entropy matrix composites.
As the optimal composition for magnetic HEAs becomes more estab­
lished, the research on LPBF-fabricated magnetic HEAs is expected to
increase because of the high dimensional accuracy of the technique
compared to other additive manufacturing techniques. Additionally,
shape memory, catalytic, and irradiation properties are expected to
garner huge interest as the field continues to grow.
6. Potential applications
The fabrication of HEAs has proven difficult because of their multielement nature, resulting in elemental segregation and other process­
ing defects. This complexity makes it challenging to identify industrial
niches where they can compete with conventional alloys. Notwith­
standing, the advent of LPBF offers a solution, with multiple research
groups demonstrating the technological potential of HEAs by printing
industrial parts (Fig. 35). LPBF-fabricated HEAs are now being consid­
ered in multiple industries, including the energy, aerospace, and
biomedical industries. Moreover, LPBF-fabricated HEAs have potential
applications in 4D printing, hydrogen storage, water-splitting, and soft
magnetic components. This section highlights the current applications of
LPBF-fabricated HEAs and explores potential future uses.
6.1. Energy industry
The energy sector faces tremendous challenges as more efficient
energy conversion and a rapid switch from fossil fuels to renewable
resources are necessary to limit the modern industry’s stress on the
environment [16]. The combination of LPBF and HEAs holds great
promise in reducing harmful emissions because of reduced weight
through compositional and structural design, more efficient material
use, and decreased reliance on scarce rare earth metals [13,104].
Herein, the applications of LPBF-fabricated HEAs in the hydrogen
economy, magnetic components in electrical power generation, and
nuclear power plants are discussed.
Emerging as a promising alternative to fossil fuels, the hydrogen
economy has seen rapid development in recent years. Notwithstanding,
numerous challenges remain, including the development of effective
fuel cells, hydrogen storage, and sustainable methods to generate
hydrogen. Fuel cells are the engines of the hydrogen economy,
33
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 35. Industrial components consisting of LPBF-fabricated HEAs, including a CrFeCoNiAl0.5 3d transition metal HEA [132], a Ni2.1AlCrFeCo eutectic HEA [32,128,
129,351], an (FeCoNi)86Al7Ti7 precipitation-strengthened HEA [173], and (TiZr)1.4(NbMoTa)0.6 and NbMoTaW refractory HEAs [38,119].
converting the stored gas into electricity. They consist of multiple
important components, among which the bipolar flow plates are typi­
cally referred to as the most critical one, accounting for 20–30% and
60–80% of the total weight and cost of the entire fuel cell, respectively
[352]. An intricate pattern of flow channels covers the surface of the
bipolar plates, and an optimal design of these flow channels is crucial for
fuel cell performance. LPBF has been investigated as a fabrication
technique for Inconel 625 and stainless steel 316 L bipolar flow plates to
allow for accurate control over the patterning of gas canals [353,354].
Particularly, LPBF has shown promise for fabricating small-scale micro
fuel cells [355].
The bipolar plates must withstand an extremely corrosive environ­
ment with high potential differences, high operating temperatures, and
low pH [320,352]. Recently, it was demonstrated that a heat treatment
at 800 ◦ C could improve the stability of the oxide layer formed on
LPBF-fabricated CrMnFeCoNi in a simulated cathodic environment of a
fuel cell, highlighting the applicability of LPBF-fabricated HEAs [320].
Additionally, LPBF-fabricated interstitial HEAs could be promising
candidates for bipolar plates as physical vapor–deposited thin films of
this class have demonstrated good performance in fuel cell environ­
ments [326,356]. By further optimizing the chemical composition of
LPBF-fabricated HEAs, materials for multiple fuel cell applications can
be designed, including micro fuel cells, proton exchange membrane fuel
cells, and solid oxide fuel cells. Moreover, if the hydrogen embrittlement
resistance of LPBF-fabricated HEAs can be improved, the alloys can
serve as intricate pipeline components for the hydrogen economy as well
as valves and nozzles for the oil and gas industry.
Soft magnetic materials are essential for modern technological sys­
tems, but they face several drawbacks, including high cost, poor me­
chanical properties, and complex manufacturing processes [349,357].
Commercial soft magnetic alloys, such as Supermalloy, silicon steels,
Permendur, MPP core, and High-Flux, are integral to efficient electrical
motors, transformers, and generators [349,357]. Magnetic HEAs have
the potential to solve many of the issues that accompany conventional
soft magnets, while LPBF can optimize the components to be lightweight
because of their unrivaled geometrical accuracy. While the magnetic
and mechanical properties of LPBF-fabricated HEAs still require signif­
icant improvement [42,348], this area demonstrates immense potential
as ~40% of global electricity production is taken up by machines
containing soft magnetic components [358].
Nuclear power is among the most effective methods of generating
electricity, and the development of advanced materials for nextgeneration reactors promises decreased environmental load and
improved safety [359]. HEAs can be designed for nuclear applications
by incorporating refractory elements with good transmutation resis­
tance and low neutron capture cross section to allow for outstanding
irradiation resistance [360,361]. The irradiation resistance of
LPBF-fabricated precipitation-strengthened (FeCoNi)86Al7Ti7 HEAs was
investigated in ref. [362]. It was confirmed that the size and number
density of helium bubbles reduced after annealing at 780 ◦ C, thus
ensuring that the precipitation-strengthened HEAs could reach their
optimal strength with improved irradiation resistance. Using
LPBF-printed precipitation-strengthened and refractory HEAs, particu­
larly those containing a high W, Zr, Ti, and V content presents a
promising strategy to fabricate in-vessel subcomponents for continu­
ously operating light water reactors, generation-five fission reactors,
and future fusion reactors [360,363].
6.2. Aerospace industry
The aerospace industry has grown immensely in recent years, spur­
ring the demand for advanced materials capable of superior perfor­
mance and high reliability under extreme environments [364]. As
evident from Fig. 35, most LPBF-fabricated HEAs were designed for the
aerospace industry, as most fabricated components resemble turbine
blades and heat sink fans. The HEA design concept holds great promise
in developing novel lightweight alloys by substituting heavier elements
with lighter ones. The Ti35Be20Al20Si15Fe10 HEA demonstrates more
than twice the specific strength of the most heavily employed com­
mercial alloy for aerospace applications, TiAl6V4 [365]. AlSiMnFe
[366] and AlTiVCr [367] have demonstrated exceptional corrosion
resistance while maintaining a low density and cost. While using ele­
ments with different melting and boiling points poses a challenge for
developing lightweight HEAs for LPBF, attempts have been made to
reduce their density through compositional design [47]. Changing the
composition from CrMnFeCoNi to (CrMnFeCoNi)91Al9 resulted in a
7.3% reduction in density while a simple heat treatment step can
significantly enhance the mechanical properties [47].
34
­
­
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
The excellent mechanical properties of LPBF-fabricated HEAs at
elevated temperatures make them promising alloys for turbine blades as
the engine can operate at a higher temperature [23,157,159], which
increases the efficiency of the turbine while reducing its operating cost
and pollution [364]. Precipitation-strengthened HEAs hold great
promise due to their microstructural similarities to the Ni-based super­
alloys commonly employed in turbine blades. Refractory HEAs can
retain their high strength at elevated temperatures [23] while the
high-temperature creep resistance of a high-entropy matrix composite
(CrCoNi)96.9W0.95Al0.65Nb0.47Re0.47Ti0.30C0.24–Y2O3 dwarfs that of
other state-of-the-art LPBF-fabricated alloys [27]. These examples,
coupled with the potential to improve the resistance to hydrogen
embrittlement, also demonstrate outstanding potential for stationary
hydrogen-fueled gas turbines [368]. However, further investigations on
enhancing the oxidation resistance are necessary before LPBF-printed
HEAs can be employed in high-temperature applications (Section
5.2.3.). The performance could be further improved by coating the
blades with a high-entropy thermal barrier coating, such as Al30Cr23
Ni23Co22Si2 [369] or (Sm0.2Eu0.2Tb0.2Dy0.2Lu0.2)2Zr2O7 [370]. Another
extreme environment where conventionally fabricated HEAs have
demonstrated huge potential is under cryogenic conditions [11,311]. As
more studies on the mechanical performance of LPBF-fabricated HEAs at
cryogenic temperatures become available, the interest in using
LPBF-fabricated HEAs in the space and chemical industries, is predicted
to increase.
Other classes of LPBF-fabricated HEAs suitable for the aerospace
industry include eutectic and metastable HEAs. The excellent print­
ability of eutectic HEAs, particularly that of Ni2.1AlCrFeCo, is advanta­
geous for fabricating components with intricate geometry, thereby
enabling topological optimization for low weight [32,128,129]. Fig. 35
shows that Ni2.1AlCrFeCo has been used to fabricate auxetic meta­
materials (i.e., materials with a negative Poisson’s ratio) [351]. Such
components have potential in defense applications due to their high
energy absorption capacity and enhanced shear, indentation, and frac­
ture resistance [371,372]. The successful fabrication of a 3D
double-arrowed structure also indicates that LPBF-fabricated HEAs
could be used as other mechanical metamaterials such as high
strength-to-weight stacked Miura-ori and pentamode structures [17].
The higher proportion of light elements in metastable HEAs warrants
investigations of their potential use in the aerospace industry, particu­
larly for alloys with a high Si content [37,162,226]. Given the concern
for catastrophic fatigue failure within the aerospace industry [373] and
the remarkable fatigue life of LPBF-fabricated metastable Fe40Mn20
Co20Cr15Si5 [162], this class of HEAs could find a highly competitive
niche in aviation applications.
reducing the valence electron concentration [224] while the structural
design reduces the elastic modulus by fabricating Gyroid structures with
different levels of porosity (Fig. 36a) [161]. LPBF-fabricated BioHEAs
offer similar biocompatibility as titanium and more widespread cell
morphology than stainless steel 316L (SS316L) (Figs. 36b and c) [38,
224]. Another essential requirement of the biomedical industry is the
anti-bacterial properties of the employed alloy. LPBF-fabricated CrFe­
CoNiCu demonstrated anti-bacterial properties against E. coli and
S. aureus bacteria due to a high release rate of Cu ions [200]. Alterna­
tively, if a more biocompatible alloy is desired, replacing Cu with Ti
yields an HEA with better cytocompatibility than pure Ti, attributed to a
combination of beneficial valence electron configuration, lattice
distortion, and formed surface oxides [315]. Similarly, it is envisioned
that by utilizing other biocompatible metals as principal elements in
HEAs, such as Zn [381] and Mg [382], multiple novel BioHEAs can be
designed.
6.4. Emerging fields
While LPBF-fabricated HEAs are considered for the above applica­
tions due to their impressive mechanical properties, they also possess
other attributes that could make them highly suitable for functional
applications, including 4D printing, hydrogen storage, and catalysis.
Nevertheless, the combination of LPBF and HEAs is yet to be explored in
designing materials for these applications, and thus, they represent
promising emerging fields where these materials could find competitive
niches.
4D printing pertains to fabricating parts capable of changing their
geometry, properties, and/or functionalities when subjected to external
stimuli, such as temperature, magnetic fields, or moisture content, using
additive manufacturing [383]. This is typically realized by the 3D
printing of intelligent shape memory alloys, of which Ni-rich NiTi has
seen the most success [384,385]. Multiple shape memory HEAs have
been designed by substituting Ti and Ni with refractory and 3d transition
metal elements [256,386,387]. Thus, if the formation of secondary
phases can be suppressed, refractory HEAs alloyed with 3d transition
metal elements such as Ni, Co, and Cu may pave the way for the 4D
printing of HEAs. Additionally, metastable HEAs are similar in elemental
and phase composition to LPBF-fabricated Fe-based shape memory al­
loys [229,230] while non-equiatomic Cr–Mn–Fe–Co HEAs [388] have
presented promising shape memory performance. Given the excellent
printability of metastable and 3d transition metal HEAs, investigations
of such alloys present an alternative route to 4D printing. Particularly,
the excellent printability of metastable HEAs indicates that
Fe54.6Mn20.7Cr9.4Si10.5Ni4.8 shape memory HEAs [389] can be highly
suitable for 4D printing.
Several hydrogen storage methods exist, but the most promising is
storage as metal hydrides due to their high volumetric energy density
and safety [390–392]. Refractory HEAs have demonstrated good
hydrogen storage capabilities, with (VTi)0.3Cr0.25Mn0.1Nb0.05 [393],
V30Fe30(TiCrCo)38Zr2 [394], and (TiVNb)85Cr15 [395] showing superior
performance in terms of gravimetric energy density. The hydrogen
storage properties have been investigated for HEAs fabricated by other
additive manufacturing technologies. It was concluded that the
as-printed microstructure is superior to that of heat-treated HEAs as the
grain boundary and dislocation substructures facilitated the diffusion of
hydrogen into the alloy [396–398]. While the hydrogen storage prop­
erties of LPBF-fabricated HEAs are yet to be explored, reports stating
that a hierarchical microstructure is beneficial for hydrogen storage
warrant such exploration [399].
A major hurdle for the hydrogen economy is its reliance on kineti­
cally slow chemical reactions, such as the oxygen reduction, hydrogen
evolution, and oxygen evolution reactions, which all require expensive
precious-metal catalysts [400]. In attempts to reduce the cost of these
catalysts, the HEA design concept has been employed to dilute the
expensive elements with more affordable ones. The multi-element
6.3. Biomedical industry
Both LPBF and HEAs have attracted the attention of the biomedical
industry, with LPBF being capable of fabricating personalized implants
catered to the patients’ individual needs [374–376]. HEAs consisting of
non-toxic elements also allow for a tunable elastic modulus and low
release rate of metal ions in corrosive body fluids. Notably, refractory
HEAs have garnered increasing attention as biomaterials as the con­
stituent elements have both high biocompatibility and corrosion resis­
tance [377,378], granting this group the name biomedical HEAs
(BioHEAs) [379]. As LPBF has already been employed to fabricate re­
fractory alloys for biomedical applications [380], a natural extension is
to fabricate BioHEAs using LPBF. The rapid cooling rate of LPBF miti­
gates the elemental segregation commonly observed in conventionally
manufactured BioHEAs, resulting in more homogenous osteoblast
adhesion [38,161,224].
Extensive efforts have been made to design BioHEAs with an elastic
modulus similar to that of the human bone to address the issue of stress
shielding, either through compositional or structural design [161,224].
The compositional design aims at reducing the elastic modulus by
35
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
Fig. 36. LPBF-fabricated BioHEAs: (a) Models of triply periodic minimal surface lattice with different porosity based on Schoen’s gyroid unit cell and the macro­
scopic morphology of LPBF-printed Ti1.5ZrNbMo0.5Ta0.5 lattices [161]. Fluorescent images of osteoblast adhesion on (b) cast SS316L and LPBF-fabricated
(TiZr)1.4(NbMoTa)0.6, and (c) cast SS316L and LPBF-fabricated Ti28.33Zr28.33Hf28.33Nb6.74Ta6.74Mo1.55 [38,224].
nature of HEAs allows for multiple absorption sites with locally varying
electronic properties, resulting in a broad range of adsorption energy
that may optimize the catalytic properties of HEAs [401]. Alloys such as
CrMnFeCoNi and MnFeCoNi have demonstrated superior catalytic
properties to Pt and RuO2 [402,403]. Recently, LPBF coupled with
chemical dealloying was leveraged to create a hierarchically porous
structure with high catalytic activity [404]. Thus, the fabrication of
HEAs through LPBF as a catalytic material for the hydrogen economy
and beyond presents a promising application field.
Although no HEA is currently employed in real industrial applica­
tions, the promising synergy between the alloys and LPBF has caused
them to be considered for energy, aerospace, and biomedical applica­
tions, where their outstanding properties are desired. As the field grows,
4D printing, hydrogen storage, and catalysis are predicted to be
emerging fields for HEAs prepared by LPBF. Ultimately, the industrial
adoption of LPBF-fabricated HEAs hinges on the successful use of sus­
tainable alloy design, and comprehensive life cycle analysis is required
to ensure that the benefits of using multiple principal elements outweigh
the drawbacks.
display superior elongation. As research progresses, it is crucial to delve
deeper into fatigue, creep, oxidation resistance, and functional proper­
ties to fully realize the potential of LPBF-fabricated HEAs as engineering
materials. Although these HEAs have not yet secured a specific industrial
niche, they are promising candidates for energy, aerospace, and
biomedical applications. Several proof-of-concept components have
already been fabricated, showcasing their high potential.
Although the combination of HEA and LPBF shows great promise
with multiple material systems demonstrating excellent printability and
outstanding properties, several challenges must be addressed to achieve
industrial applications. In addition to the challenges already discussed in
Sections 2–6, key obstacles include the need for high-throughput ex­
periments to explore new HEA classes for LPBF and further the expan­
sion of existing HEA classes.
The rapidly developing high-throughput simulations spearheaded by
machine learning enable computational screening of an extensive
compositional space. However, these simulations require corresponding
high-throughput experiments to match the computational speed and
generate datasets for the algorithms. The LPBF technique is mainly
suitable for fabricating a single composition, which limits its effective­
ness for high-throughput experimental screening. While some other
additive manufacturing techniques, such as directed energy deposition,
are well-suited for high-throughput screening, the difference in pro­
cessing conditions means that the developed alloys might not be suitable
for the LPBF process [21]. A recently developed single-melt-track plat­
form has rapidly screened the crack susceptibility and solidification
microstructure of conventional and multicomponent refractory alloys,
circumventing the need for expensive powder feedstock [405]. Other
work has attempted to print compositionally graded HEAs using a
modified LPBF machine, which also has the potential to enable the
fabrication of functionally graded HEAs and high-performance parts
with spatially controlled composition [406,407]. Further efforts should
be aimed at developing such technologies to accelerate the experimental
exploration of novel HEAs.
As highlighted earlier, not all classes of HEAs have been investigated
for LPBF. For instance, shape memory HEAs, lightweight HEAs,
precious-metal HEAs, or high-entropy bronzes have yet to be extensively
fabricated by LPBF. Given the broad adoption of LPBF in the aerospace
industry [408], lightweight HEAs should be of significant interest. Al­
loys such as Ti35Be20Al20Si15Fe10 [365], AlSiMnFe [366], and MgAlTi­
FeZn [409] could be considered if the issue with evaporation of
low-boiling-point elements can be solved. High-entropy bronze, devel­
oped to enhance the strength of conventional bronze, warrants exami­
nation for LPBF because of the growing interest in using bronze for
additive manufacturing [322,410]. While the LPBF-fabricated
NiCuRhPdIrPt HEA qualifies as a precious-metal HEA [255], it has not
been studied for catalytic purposes, which is a primary motivation for
7. Conclusion and perspectives
The continuous growth of LPBF-fabricated HEAs has utilized various
design strategies to achieve promising material properties while over­
coming the challenges of working with complex chemical compositions.
To date, seven main classes of HEAs have been successfully fabricated
via LPBF: 3d transition metal HEAs, eutectic HEAs, precipitationstrengthened HEAs, refractory HEAs, metastable HEAs, interstitial
HEAs, and high-entropy matrix composites. Computational modeling
has played a crucial role in compositional and process optimization,
accelerating the field’s development. The advantages and limitations of
these techniques are comprehensively summarized in Section 2. Most
classes of HEAs are prepared using gas-atomized powder feedstock for
its superior quality. However, refractory HEAs and high-entropy matrix
composites often require specific constituent elements and extrinsic
particles, respectively, as detailed in Section 3. The printability of the
different HEA classes is thoroughly reviewed, with guidelines provided
to mitigate processing defects and enhance the part quality. Section 4
extensively discusses the microstructure of LPBF-fabricated HEAs,
focusing on grain texture, phase composition, and elemental
segregation.
Section 5 explores the diverse mechanical, physical, and chemical
properties of LPBF-fabricated HEAs. The tensile test is the primary
method for assessing mechanical properties, showing distinct trends
across different HEA classes. Eutectic HEAs exhibit the highest yield
strength in their as-printed states, followed by high-entropy matrix
composites, while metastable, 3d transition metal, and interstitial HEAs
36
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
this class. Therefore, it is necessary to explore whether the LPBF tech­
nique, combined with further chemical treatment, can enhance the
catalytic properties of precious-metal HEAs.
Significant research is still required across the different classes of
HEAs. The development of new methods to fabricate spherical refractory
HEA powder particles suitable for LPBF, such as the plasma rotating
electrode process [411,412], is expected to increase the application of
refractory HEAs in LPBF. Additionally, adding elements with a low
melting point may improve the printability of existing refractory HEAs.
Similarly, the fabrication of eutectic HEAs by LPBF is just in its infancy,
with many eutectic HEAs prepared by conventional techniques yet to be
fabricated via LPBF [34]. The production of metastable HEAs by LPBF
remains a promising research area, with new strategies being explored
to reduce the stability of the solid-solution phase. Different TRIP
mechanisms other than the commonly observed FCC-to-HCP mechanism
should be explored. For example, V-containing metastable HEAs have
been reported to exhibit an FCC-to-BCC transformation, which is said to
yield enhanced work hardening and hence warrants exploration [413,
414]. Finally, applying the concept of metastability to LPBF-fabricated
refractory HEAs could potentially improve the printability and
ductility of such alloys.
While interstitial HEAs exhibit good mechanical properties [30,225,
236], the formation of Cr23C6 will lead to Cr segregation and potentially
reduce the corrosion resistance, similar to the case of stainless steel
[415]. The effect of carbide formation on the corrosion resistance of
C-doped interstitial HEAs needs to be thoroughly examined to ensure
their durability. Additionally, the effects of adding C and N should be
explored in other LPBF-fabricated HEAs, including eutectic and
precipitation-strengthened HEAs. Investigating alloying elements such
as V, Ta, Nb, and Mo is crucial to better control the precipitates’ volume
fraction, size, and stability at elevated temperatures for
precipitation-strengthened HEAs.
Extensive efforts are needed to test LPBF-fabricated HEAs in simu­
lated application environments, reflecting conditions in the energy,
aerospace, and biomedical industries. A comprehensive life cycle anal­
ysis is essential to ensure that these alloys are environmentally sus­
tainable and can compete financially with state-of-the-art alloys in their
respective sectors. Additionally, expanding the application of the HEAs
into the hydrogen economy, 4D printing, and 3D-printed catalysts rep­
resents promising future research areas for the community to explore.
As the fabrication of HEAs using LPBF continues to garner increasing
attention, it is anticipated that many new HEAs with excellent print­
ability and outstanding properties will be developed. Given the
impressive material properties that the small fraction of explored HEAs
have demonstrated, it is reasonable to infer that ongoing research will
provide society with sustainable alloys suitable for challenging indus­
trial applications where the strength of both HEAs and LPBF can be fully
utilized.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.
Data Availability
No data were used for the research described in the article.
Acknowledgement
The financial support from the A*STAR Structural and Metal Alloys
Programme (SMAP): Work Package II (Grant No. A18B1b0061) is
acknowledged. The financial support from 4D Additive Manufacturing
(4DAM) of Smart Structures (Grant No. M24N3b0028) under RIE2025
Manufacturing, Trade and Connectivity (MTC) Programmatic Fund is
acknowledged. A. Jarlöv, W. Ji, S. Gao, P. Vivegananthan, Y. Tian, D.
Kripalani, and K. Zhou acknowledge the financial support offered by
Nanyang Technological University. A. Jarlöv is grateful for the ongoing
research scholarship, Singapore International Graduate Award (SINGA),
from the A*STAR Graduate Academy.
References
[1] Z. Zhu, W. Li, Q.B. Nguyen, X. An, W. Lu, Z. Li, et al., Enhanced strength–ductility
synergy and transformation-induced plasticity of the selective laser melting
fabricated 304L stainless steel, pp. 101300-1–10, Addit. Manuf. 35 (2020),
https://doi.org/10.1016/j.addma.2020.101300.
[2] T. Zhang, C.-T. Liu, Design of titanium alloys by additive manufacturing: A
critical review, pp. 100014-1–11, Adv. Powder Mater. 1 (1) (2022), https://doi.
org/10.1016/j.apmate.2021.11.001.
[3] Z. Zhu, Z. Hu, H.L. Seet, T. Liu, W. Liao, U. Ramamurty, et al., Recent progress on
the additive manufacturing of aluminum alloys and aluminum matrix composites:
Microstructure, properties, and applications, Int. J. Mach. Tools Manuf. 190
(2023) 1–48, https://doi.org/10.1016/j.ijmachtools.2023.104047, 104047.
[4] S. Sanchez, P. Smith, Z. Xu, G. Gaspard, C.J. Hyde, W.W. Wits, et al., Powder bed
fusion of nickel-based superalloys: A review, pp. 103729-1–77, Int. J. Mach. Tools
Manuf. 165 (2021), https://doi.org/10.1016/j.ijmachtools.2021.103729.
[5] B. Cantor, I.T.H. Chang, P. Knight, A.J.B. Vincent, Microstructural development
in equiatomic multicomponent alloys, Mater. Sci. Eng.: A 375 (2004) 213–218,
https://doi.org/10.1016/j.msea.2003.10.257.
[6] J.W. Yeh, S.K. Chen, S.J. Lin, J.Y. Gan, T.S. Chin, T.T. Shun, et al.,
Nanostructured high-entropy alloys with multiple principal elements: novel alloy
design concepts and outcomes, Adv. Eng. Mater. 6 (5) (2004) 299–303, https://
doi.org/10.1002/adem.200300567.
[7] Z. Fu, L. Jiang, J.L. Wardini, B.E. MacDonald, H. Wen, W. Xiong, et al., A highentropy alloy with hierarchical nanoprecipitates and ultrahigh strength, pp.
eaat8712-1–8, Sci. Adv. 4 (10) (2018), https://doi.org/10.1126/sciadv.aat8712.
[8] P. Shi, R. Li, Y. Li, Y. Wen, Y. Zhong, W. Ren, et al., Hierarchical crack buffering
triples ductility in eutectic herringbone high-entropy alloys, Science 373 (6557)
(2021) 912–918, https://doi.org/10.1126/science.abf6986.
[9] Y. Qiu, S. Thomas, B. Fabijanic, A.J. Barlow, H.L. Fraser, N. Birbilis,
Microstructural evolution, electrochemical and corrosion properties of
AlxCoCrFeNiTiy high entropy alloys, pp. 107698-1–15, Mater. Des. 170 (2019),
https://doi.org/10.1016/j.matdes.2019.107698.
[10] S. Xia, W. Zhen, T. Yang, Y. Zhang, Irradiation behavior in high entropy alloys,
J. Iron Steel Res., Int. 22 (10) (2015) 879–884, https://doi.org/10.1016/S1006706X(15)30084-4.
[11] D. Liu, Q. Yu, S. Kabra, M. Jiang, P. Forna-Kreutzer, R. Zhang, et al., Exceptional
fracture toughness of CrCoNi-based medium-and high-entropy alloys at 20 kelvin,
Science 378 (6623) (2022) 978–983, https://doi.org/10.1126/science.abp8070.
[12] Y. Mizuguchi, M.R. Kasem, T.D. Matsuda, Superconductivity in CuAl2-type Co0.
2Ni0. 1Cu0. 1Rh0. 3Ir0. 3Zr2 with a high-entropy-alloy transition metal site,
Mater. Res. Lett. 9 (3) (2021) 141–147, https://doi.org/10.1080/
21663831.2020.1860147.
[13] D.B. Miracle, O.N. Senkov, A critical review of high entropy alloys and related
concepts, Acta Mater. 122 (2017) 448–511, https://doi.org/10.1016/j.
actamat.2016.08.081.
[14] C. Han, Q. Fang, Y. Shi, S.B. Tor, C.K. Chua, Z. Kun, Recent advances on highentropy alloys for 3D printing, pp. 1903855-1–41, Adv. Mater. 32 (26) (2020),
https://doi.org/10.1002/adma.201903855.
[15] X. Fu, C.A. Schuh, E.A. Olivetti, Materials selection considerations for high
entropy alloys, Scr. Mater. 138 (2017) 145–150, https://doi.org/10.1016/j.
scriptamat.2017.03.014.
[16] D. Raabe, The materials science behind sustainable metals and alloys, Chem. Rev.
123 (5) (2023) 2436–2608, https://doi.org/10.1021/acs.chemrev.2c00799.
CRediT authorship contribution statement
Asker Jarlöv: Writing – original draft, Methodology, Investigation,
Formal analysis, Data curation, Conceptualization. Zhiguang Zhu:
Writing – review & editing, Methodology, Conceptualization. Weiming
Ji: Writing – review & editing, Conceptualization. Shubo Gao: Writing –
review & editing, Conceptualization. Zhiheng Hu: Writing – review &
editing. Priyanka Vivegananthan: Writing – review & editing. Yujia
Tian: Writing – review & editing. Devesh Kripalani: Writing – review &
editing. Haiyang Fan: Writing – review & editing. Hang Li Seet:
Writing – review & editing. Changjun Han: Writing – review & editing.
Liming Tan: Writing – review & editing. Feng Liu: Writing – review &
editing. Mui Ling Sharon Nai: Writing – review & editing, Supervision,
Resources, Project administration, Methodology, Funding acquisition,
Conceptualization. Kun Zhou: Writing – review & editing, Supervision,
Resources, Methodology, Funding acquisition, Conceptualization.
37
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
[17] K. Zhou, C. Han, Metal Powder–Based Additive Manufacturing, Wiley-VCH
GmbH, Weinheim, 2023. ISBN: 978-3-527-34631-8.
[18] S. Gao, Z. Li, S.V. Petegem, J. Ge, S. Goel, J.V. Vas, et al., Additive manufacturing
of alloys with programmable microstructure and properties, pp. 6752-1–11, Nat.
Commun. 14 (1) (2023), https://doi.org/10.1038/s41467-023-42326-y.
[19] Z. Zhu, F.L. Ng, H.L. Seet, W. Lu, C.H. Liebscher, Z. Rao, et al., Superior
mechanical properties of a selective-laser-melted AlZnMgCuScZr alloy enabled by
a tunable hierarchical microstructure and dual-nanoprecipitation, Mater. Today
52 (2022) 90–101, https://doi.org/10.1016/j.mattod.2021.11.019.
[20] A. Bandyopadhyay, K.D. Traxel, M. Lang, M. Juhasz, N. Eliaz, S. Bose, Alloy
design via additive manufacturing: advantages, challenges, applications and
perspectives, Mater. Today 52 (2022) 207–224, https://doi.org/10.1016/j.
mattod.2021.11.026.
[21] T. DebRoy, H. Wei, J. Zuback, T. Mukherjee, J. Elmer, J. Milewski, et al., Additive
manufacturing of metallic components–process, structure and properties, Prog.
Mater. Sci. 92 (2018) 112–224, https://doi.org/10.1016/j.pmatsci.2017.10.001.
[22] Z. Sun, X.P. Tan, M. Descoins, D. Mangelinck, S.B. Tor, C.S. Lim, Revealing hot
tearing mechanism for an additively manufactured high-entropy alloy via
selective laser melting, Scr. Mater. 168 (2019) 129–133, https://doi.org/
10.1016/j.scriptamat.2019.04.036.
[23] H. Zhang, Y. Zhao, J. Cai, S. Ji, J. Geng, X. Sun, et al., High-strength NbMoTaX
refractory high-entropy alloy with low stacking fault energy eutectic phase via
laser additive manufacturing, pp. 109462-1–15, Mater. Des. 201 (2021), https://
doi.org/10.1016/j.matdes.2021.109462.
[24] Z. Sun, X. Tan, C. Wang, M. Descoins, D. Mangelinck, S.B. Tor, et al., Reducing
hot tearing by grain boundary segregation engineering in additive manufacturing:
example of an AlxCoCrFeNi high-entropy alloy, pp. 116505-1–14, Acta Mater.
204 (2021), https://doi.org/10.1016/j.actamat.2020.116505.
[25] R. Li, P. Niu, T. Yuan, Z. Li, Displacive transformation as pathway to prevent
micro-cracks induced by thermal stress in additively manufactured strong and
ductile high-entropy alloys, Trans. Nonferrous Met. Soc. China 31 (4) (2021)
1059–1073, https://doi.org/10.1016/S1003-6326(21)65561-9.
[26] C. Pan, X. Li, H. Luo, K. Kosiba, S. Qu, C. Yang, et al., Tuning the strength and
ductility balance of a Co32Cr36Ni32 medium entropy alloy fabricated by
selective laser melting: effect of segregations along grain boundaries, pp. 1429231–5, Mater. Sci. Eng.: A (2022), https://doi.org/10.1016/j.msea.2022.142923.
[27] T.M. Smith, C.A. Kantzos, N.A. Zarkevich, B.J. Harder, M. Heczko, P.R. Gradl, et
al., A 3D printable alloy designed for extreme environments, Nature 617 (2023)
513–518, https://doi.org/10.1038/s41586-023-05893-0.
[28] B. Li, B. Qian, Y. Xu, Z. Liu, F. Xuan, Fine-structured CoCrFeNiMn high-entropy
alloy matrix composite with 12 wt% TiN particle reinforcements via selective
laser melting assisted additive manufacturing, Mater. Lett. 252 (2019) 88–91,
https://doi.org/10.1016/j.matlet.2019.05.108.
[29] J.G. Kim, J.M. Park, J.B. Seol, J. Choe, J.-H. Yu, S. Yang, et al., Nano-scale solute
heterogeneities in the ultrastrong selectively laser melted carbon-doped
CoCrFeMnNi alloy, pp. 138726-1–9, Mater. Sci. Eng.: A 773 (2020), https://doi.
org/10.1016/j.msea.2019.138726.
[30] M. Song, R. Zhou, J. Gu, Z. Wang, S. Ni, Y. Liu, Nitrogen induced heterogeneous
structures overcome strength-ductility trade-off in an additively manufactured
high-entropy alloy, pp. 100498-1–6, Appl. Mater. Today 18 (2020), https://doi.
org/10.1016/j.apmt.2019.100498.
[31] Z. Gu, X. Su, W. Peng, W. Guo, S. Xi, X. Zhang, et al., An important improvement
of strength and ductility on a new type of CoCr2. 5FeNi2TiW0. 5 high entropy
alloys under two different protective gases by selective laser melting, pp. 1590881–11, J. Alloy. Compd. 868 (2021), https://doi.org/10.1016/j.
jallcom.2021.159088.
[32] J. Ren, Y. Zhang, D. Zhao, Y. Chen, S. Guan, Y. Liu, et al., Strong yet ductile
nanolamellar high-entropy alloys by additive manufacturing, Nature 608 (7921)
(2022) 62–68, https://doi.org/10.1038/s41586-022-04914-8.
[33] Y. Lu, X. Wu, Z. Fu, Q. Yang, Y. Zhang, Q. Liu, et al., Ductile and ultrahighstrength eutectic high-entropy alloys by large-volume 3D printing, J. Mater. Sci.
Technol. 126 (2022) 15–21, https://doi.org/10.1016/j.jmst.2022.04.004.
[34] Y. Lu, Y. Dong, H. Jiang, Z. Wang, Z. Cao, S. Guo, et al., Promising properties and
future trend of eutectic high entropy alloys, Scr. Mater. 187 (2020) 202–209,
https://doi.org/10.1016/j.scriptamat.2020.06.022.
[35] J.M. Park, P. Asghari-Rad, A. Zargaran, J.W. Bae, J. Moon, H. Kwon, et al., Nanoscale heterogeneity-driven metastability engineering in ferrous medium-entropy
alloy induced by additive manufacturing, pp. 117426-1–13, Acta Mater. 221
(2021), https://doi.org/10.1016/j.actamat.2021.117426.
[36] P. Agrawal, S. Thapliyal, S.S. Nene, R.S. Mishra, B.A. McWilliams, K.C. Cho,
Excellent strength-ductility synergy in metastable high entropy alloy by laser
powder bed additive manufacturing, pp. 101098-1–7, Addit. Manuf. 32 (2020),
https://doi.org/10.1016/j.addma.2020.101098.
[37] S. Thapliyal, S.S. Nene, P. Agrawal, T. Wang, C. Morphew, R.S. Mishra, et al.,
Damage-tolerant, corrosion-resistant high entropy alloy with high strength and
ductility by laser powder bed fusion additive manufacturing, pp. 101455-1–10,
Addit. Manuf. 36 (2020), https://doi.org/10.1016/j.addma.2020.101455.
[38] T. Ishimoto, R. Ozasa, K. Nakano, M. Weinmann, C. Schnitter, M. Stenzel, et al.,
Development of TiNbTaZrMo bio-high entropy alloy (BioHEA) super-solid
solution by selective laser melting, and its improved mechanical property and
biocompatibility, pp. 113658-1–6, Scr. Mater. 194 (2021), https://doi.org/
10.1016/j.scriptamat.2020.113658.
[39] Y. Mu, L. He, S. Deng, Y. Jia, Y. Jia, G. Wangm, et al., A high-entropy alloy with
dislocation-precipitate skeleton for ultrastrength and ductility, pp. 117975-1–14,
Acta Mater. 232 (2022), https://doi.org/10.1016/j.actamat.2022.117975.
[40] L. Xu, Y. Jia, Z. Wang, S. Wu, Y. Jia, C. Geng, et al., Dual precipitate simultaneous
enhancement of tensile and fatigue strength in (FeCoNi) 86Al7Ti7 high-entropy
alloy fabricated using selective laser melting, J. Mater. Sci. Technol. 148 (2023)
90–104, https://doi.org/10.1016/j.jmst.2022.09.068.
[41] Z. Li, P.-C. Zhao, T. Lu, K. Feng, Y. Tong, B. Sun, et al., Effects of Post Annealing
On the Microstructure, Precipitation Behavior, and Mechanical Property Of a
(CoCrNi)94Al3Ti3 Medium-Entropy Alloy Fabricated by Laser Powder Bed
Fusion, J. Mater. Sci. Technol. 135 (2023) 142–155, https://doi.org/10.1016/j.
jmst.2022.07.012.
[42] X. Song, P.K. Liaw, Z. Wei, Z. Liu, Y. Zhang, Evolution of the microstructures,
magnetic and mechanical behaviors of Co47. 5Fe28. 5Ni19Si3. 4Al1. 6 highentropy alloy fabricated by laser powder bed fusion, 103593-113, Addit. Manuf.
71 (2023), https://doi.org/10.1016/j.addma.2023.103593.
[43] W.M. Choi, Y.H. Jo, S.S. Sohn, S. Lee, B.J. Lee, Understanding the physical
metallurgy of the CoCrFeMnNi high-entropy alloy: an atomistic simulation study,
npj Comput. Mater. 4 (1) (2018) 1–9, https://doi.org/10.1038/s41524-0170060-9.
[44] P.K. Sarswat, S. Sarkar, A. Murali, W. Huang, W. Tan, M.L. Free, Additive
manufactured new hybrid high entropy alloys derived from the
AlCoFeNiSmTiVZr system, Appl. Surf. Sci. 476 (2019) 242–258, https://doi.org/
10.1016/j.apsusc.2018.12.300.
[45] S.S. Nene, M. Frank, K. Liu, R.S. Mishra, B.A. McWilliams, K.C. Cho, Extremely
high strength and work hardening ability in a metastable high entropy alloy, pp.
9920-1–8, Sci. Rep. 8 (1) (2018), https://doi.org/10.1038/s41598-018-28383-0.
[46] H. Wang, B. Li, F. Xuan, A dimensionally augmented and physics-informed
machine learning for quality prediction of additively manufactured high-entropy
alloy, pp. 117637-1–13, J. Mater. Process. Technol. 307 (2022), https://doi.org/
10.1016/j.jmatprotec.2022.117637.
[47] D. Kong, L. Wang, G. Zhu, Y. Zhou, X. Ni, J. Song, et al., Heat treatment effects on
the metastable microstructure, mechanical property and corrosion behavior of Aladded CoCrFeMnNi alloys fabricated by laser powder bed fusion, J. Mater. Sci.
Technol. 138 (2023) 171–182, https://doi.org/10.1016/j.jmst.2022.08.018.
[48] L. Johnson, M. Mahmoudi, B. Zhang, R. Seede, X. Huang, J.T. Maier, et al.,
Assessing printability maps in additive manufacturing of metal alloys, Acta Mater.
176 (2019) 199–210, https://doi.org/10.1016/j.actamat.2019.07.005.
[49] Y. Huang, Z. Xie, W. Li, H. Chen, B. Liu, B. Wang, Dynamic mechanical properties
of the selective laser melting NiCrFeCoMo0. 2 high entropy alloy and the
microstructure of molten pool, pp. 167011-1–13, J. Alloy. Compd. 927 (2022),
https://doi.org/10.1016/j.jallcom.2022.167011.
[50] I.R. Jamil, A.M. Mustaquim, M. Islam, M.N. Hasan, Molecular dynamics
perspective of the effects of laser thermal configurations on the dislocation and
mechanical characteristics of FeNiCrCoCu HEA through powder bed fusion
process, pp. 104998-1–15, Mater. Today Commun. 33 (2022), https://doi.org/
10.1016/j.mtcomm.2022.104998.
[51] J. Peng, J. Li, B. Liu, J. Wang, H. Chen, H. Feng, et al., Formation process and
mechanical properties in selective laser melted multi-principal-element alloys,
J. Mater. Sci. Technol. 133 (2023) 12–22, https://doi.org/10.1016/j.
jmst.2022.06.017.
[52] R. Tangestani, A. Chakraborty, T. Sabiston, L. Yuan, M. Ghasri-Khouzani,
É. Martin, Multi-scale model to simulate stress directionality in laser powder bed
fusion: Application to thin-wall part failure, pp. 112147-1–17, Mater. Des. 232
(2023), https://doi.org/10.1016/j.matdes.2023.112147.
[53] X. Li, N. Polydorides, Fast heat transfer simulation for laser powder bed fusion,
pp. 116107-1–21, Comput. Methods Appl. Mech. Eng. 412 (2023), https://doi.
org/10.1016/j.cma.2023.116107.
[54] B. Korneev, A. Zakirov, M. Bogdanova, S. Belousov, A. Perepelkina,
I. Iskandarova, et al., A numerical study of powder wetting influence on the
morphology of laser powder bed fusion manufactured thin walls, pp. 103705-1–,
Addit. Manuf. 74 (2023) https://doi.org/10.1016/j.addma.2023.103705.
[55] J. Kim, A. Wakai, A. Moridi, Materials and manufacturing renaissance: Additive
manufacturing of high-entropy alloys, J. Mater. Res. 35 (15) (2020) 1963–1983,
https://doi.org/10.1557/jmr.2020.140.
[56] A.O. Moghaddam, N.A. Shaburova, M.N. Samodurova, A. Abdollahzadeh, E.
A. Trofimov, Additive manufacturing of high entropy alloys: a practical review,
J. Mater. Sci. Technol. 77 (2020) 131–162, https://doi.org/10.1016/j.
jmst.2020.11.029.
[57] Z.U. Arif, M.Y. Khalid, and ur Rehman, E. Laser-aided additive manufacturing of
high entropy alloys: Processes, properties, and emerging applications, J. Manuf.
Process. 78 (2022) 131–171, https://doi.org/10.1016/j.jmapro.2022.04.014.
[58] C. Li, M. Ferry, J.J. Kruzic, X. Li, Multi-principal element alloys by additive
manufacturing, J. Mater. Sci. 57 (2022) 1–33, https://doi.org/10.1007/s10853022-06961-y.
[59] W. Zhang, A. Chabok, B.J. Kooi, Y. Pei, Additive manufactured high entropy
alloys: A review on the microstructure and properties, pp. 110875-1–40, Mater.
Des. 220 (2022), https://doi.org/10.1016/j.matdes.2022.110875.
[60] P. Das, R. Nandan, P.M. Pandey, A Review on Corrosion Properties of High
Entropy Alloys Fabricated by Additive Manufacturing, Trans. Indian Inst. Met. 75
(10) (2022) 1–12, https://doi.org/10.1007/s12666-022-02610-9.
[61] M.A. Mahmood, F.G. Alabtah, Y. Al-Hamidi, M. Khraisheh, On the laser additive
manufacturing of high-entropy alloys: A critical assessment of in-situ monitoring
techniques and their suitability, pp. 111658-1–28, Mater. Des. 226 (2023),
https://doi.org/10.1016/j.matdes.2023.111658.
[62] H. Liu, D. Yang, Q. Jiang, Y. Jiang, W. Yang, L. Liu, et al., Additive manufacturing
of metallic glasses and high-entropy alloys: Significance, unsettled issues, and
future directions, J. Mater. Sci. Technol. 140 (2023) 79–120, https://doi.org/
10.1016/j.jmst.2022.09.006.
38
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
[63] F. Haftlang, H.S. Kim, A perspective on precipitation-hardening high-entropy
alloys fabricated by additive manufacturing, pp. 110161-1–22, Mater. Des. 211
(2021), https://doi.org/10.1016/j.matdes.2021.110161.
[64] Y. Guo, H. Su, P. Yang, Y. Zhao, Z. Shen, Y. Liu, et al., A Review of Emerging
Metallic System for High-Energy Beam Additive Manufacturing: Al–Co–Cr–Fe–Ni
High Entropy Alloys, Acta Metall. Sin. (Engl. Lett. ) 35 (2022) 1407–1423,
https://doi.org/10.1007/s40195-022-01400-y.
[65] W. Cheng, L. Ji, L. Zhang, H. Wang, W. Sun, Refractory high-entropy alloys
fabricated using laser technologies: A concrete review, J. Mater. Res. Technol. 24
(2023) 7497–7524, https://doi.org/10.1016/j.jmrt.2023.05.037.
[66] J. Liu, Z. Li, D. Lin, Z. Tang, X. Song, P. He, et al., Eutectic high-entropy alloys and
their applications in materials processing engineering: A review, J. Mater. Sci.
Technol. 189 (2024) 211–246, https://doi.org/10.1016/j.jmst.2023.10.057.
[67] H. Gu, C. Wei, L. Li, Q. Han, R. Setchi, M. Ryan, et al., Multi-physics modelling of
molten pool development and track formation in multi-track, multi-layer and
multi-material selective laser melting, pp. 119458-1–16, Int. J. Heat. Mass Transf.
151 (2020), https://doi.org/10.1016/j.ijheatmasstransfer.2020.119458.
[68] Y. Sun, L. Zhao, C.J. Pickard, R.J. Hemley, Y. Zheng, M. Miao, Chemical
interactions that govern the structures of metals, pp. e2218405120-1–7, Proc.
Natl. Acad. Sci. 120 (8) (2023), https://doi.org/10.1073/pnas.2218405120.
[69] J. Kim, J.Y. Kim, E.S. Park, Pushing the Boundaries of Multicomponent Alloy
Nanostructures: Hybrid Approach of Liquid Phase Separation and Selective
Leaching Processes, Acc. Chem. Res. 55 (13) (2022) 1821–1831, https://doi.org/
10.1021/acs.accounts.2c00143?urlappend=%3Fref%
3DPDF&jav=VoR&rel=cite-as.
[70] S.Y. Lee, S. Byeon, H.S. Kim, H. Jin, S. Lee, Deep learning-based phase prediction
of high-entropy alloys: Optimization, generation, and explanation, pp. 1092601–16, Mater. Des. 197 (2021), https://doi.org/10.1016/j.matdes.2020.109260.
[71] G. Tapia, S. Khairallah, M. Matthews, W.E. King, A. Elwany, Gaussian processbased surrogate modeling framework for process planning in laser powder-bed
fusion additive manufacturing of 316L stainless steel, Int. J. Adv. Manuf. Technol.
94 (2018) 3591–3603, https://doi.org/10.1007/s00170-017-1045-z.
[72] C. Chen, H. Zhu, Z. Xiao, S. Liu, J. Yin, X. Zeng, The Residual Stress Distribution
of Ti-6Al-4V Thin Wall in the Selective Laser Melting, IOP Conf. Ser.: Mater. Sci.
Eng. 538 (2019) 1–7, https://doi.org/10.1088/1757-899X/538/1/012020.
[73] J. Li, Q. Fang, P.K. Liaw, Microstructures and Properties of High-Entropy
Materials: Modeling, Simulation, and Experiments, pp. 2001044-1–30, Adv. Eng.
Mater. 23 (1) (2020), https://doi.org/10.1002/adem.202001044.
[74] Z.H. Aitken, V. Sorkin, Y.-W. Zhang, Atomistic modeling of nanoscale plasticity in
high-entropy alloys, J. Mater. Res. 34 (9) (2019) 1509–1532, https://doi.org/
10.1557/jmr.2019.50.
[75] K. Zhou, B. Liu, Molecular Dynamics Simulation: Fundamentals and Applications,
Elsevier, Amsterdam, Netherlands, 2022. ISBN: 978-0-12-816419-8.
[76] T. Yang, Y. Zhao, W. Liu, J. Kai, C. Liu, L1 2-strengthened high-entropy alloys for
advanced structural applications, J. Mater. Res. 33 (19) (2018) 2983–2997,
https://doi.org/10.1557/jmr.2018.186.
[77] H.L. Chen, H. Mao, Q. Chen, Database development and Calphad calculations for
high entropy alloys: Challenges, strategies, and tips, Mater. Chem. Phys. 210
(2018) 279–290, https://doi.org/10.1016/j.matchemphys.2017.07.082.
[78] A.A. Martin, N.P. Calta, S.A. Khairallah, J. Wang, P.J. Depond, A.Y. Fong,
Dynamics of pore formation during laser powder bed fusion additive
manufacturing, Nat. Commun. 10 (1) (2019) 1987-1–10, https://doi.org/
10.1038/s41467-019-10009-2.
[79] C. Chen, J. Yin, H. Zhu, X. Zeng, G. Wang, L. Ke, et al., The effect of process
parameters on the residual stress of selective laser melted Inconel 718 thin-walled
part, Rapid Prototyp. J. 25 (8) (2019) 1359–1369, https://doi.org/10.1108/RPJ09-2018-0249.
[80] L. Chen, A. Jarlöv, H.L. Seet, M.L.S. Nai, Y. Li, K. Zhou, Exploration of
V–Cr–Fe–Co–Ni high-entropy alloys with high yield strength: A combination of
machine learning and molecular dynamics simulation, pp. 111888-1–10, Comput.
Mater. Sci. 217 (2023), https://doi.org/10.1016/j.commatsci.2022.111888.
[81] P. Chen, X. Yao, M.M. Attallah, M. Yan, In-situ alloyed CoCrFeMnNi high entropy
alloy: Microstructural development in laser powder bed fusion, J. Mater. Sci.
Technol. 123 (2022) 123–135, https://doi.org/10.1016/j.jmst.2021.11.083.
[82] D. Lin, L. Xu, X. Li, H. Jing, G. Qin, H. Pang, et al., A Si-containing FeCoCrNi highentropy alloy with high strength and ductility synthesized in situ via selective
laser melting, pp. 101340-1–13, Addit. Manuf. 35 (2020), https://doi.org/
10.1016/j.addma.2020.101340.
[83] D. Vogiatzief, A. Evirgen, M. Pedersen, U. Hecht, Laser powder bed fusion of an
Al-Cr-Fe-Ni high-entropy alloy produced by blending of prealloyed and elemental
powder: process parameters, microstructures and mechanical properties, pp.
165658-1–13, J. Alloy. Compd. 918 (2022), https://doi.org/10.1016/j.
jallcom.2022.165658.
[84] D. Lin, L. Xu, Y. Han, Y. Zhang, H. Jing, L. Zhao, et al., Structure and mechanical
properties of a FeCoCrNi high-entropy alloy fabricated via selective laser melting,
pp. 106963-1–10, Intermetallics 127 (2020), https://doi.org/10.1016/j.
intermet.2020.106963.
[85] Y. Hou, H. Su, H. Zhang, F. Li, X. Wang, Y. He, et al., An integrated simulation
model towards laser powder bed fusion in-situ alloying technology, pp. 1117951–16, Mater. Des. 228 (2023), https://doi.org/10.1016/j.matdes.2023.111795.
[86] S. Wu, H.Y. Chia, T. Zhang, Y. Jia, Y. Mu, Q. Zhang, et al., A precipitation
strengthened high entropy alloy with high (Al+ Ti) content for laser powder bed
fusion: Synergizing in trinsic hot cracking resistance and ultrahigh strength, pp.
119193-1–17, Acta Mater. 258 (2023), https://doi.org/10.1016/j.
actamat.2023.119193.
[87] Y.T. Tang, C. Panwisawas, J.N. Ghoussoub, Y. Gong, J.W. Clark, A.A. Németh, et
al., Alloys-by-design: Application to new superalloys for additive manufacturing,
Acta Mater. 202 (2021) 417–436, https://doi.org/10.1016/j.
actamat.2020.09.023.
[88] J.C. Lippold, S.D. Kiser, J.N. DuPont, Welding metallurgy and weldability of
nickel-base alloys, John Wiley & Sons, Hoboken, New Jersey, 2011. ISBN: 978-0470-08714-5.
[89] S. Nene, M. Frank, K. Liu, S. Sinha, R. Mishra, B. McWilliams, et al., Reversed
strength-ductility relationship in microstructurally flexible high entropy alloy,
Scr. Mater. 154 (2018) 163–167, https://doi.org/10.1016/j.
scriptamat.2018.05.043.
[90] Q. Wu, Z. Wang, X. Hu, T. Zheng, Z. Yang, F. He, et al., Uncovering the eutectics
design by machine learning in the Al–Co–Cr–Fe–Ni high entropy system, Acta
Mater. 182 (2020) 278–286, https://doi.org/10.1016/j.actamat.2019.10.043.
[91] J. Ren, M. Wu, C. Li, S. Guan, J. Dong, J.-B. Forien, et al., Deformation
mechanisms in an additively manufactured dual-phase eutectic high-entropy
alloy, pp. 119179-1–17, Acta Mater. 257 (2023), https://doi.org/10.1016/j.
actamat.2023.119179.
[92] Y. Zeng, M. Man, C.K. Ng, Z. Aitken, K. Bai, D. Wuu, et al., Search for eutectic
high entropy alloys by integrating high-throughput CALPHAD, machine learning
and experiments, pp. 112929-1–12, Mater. Des. 241 (2024), https://doi.org/
10.1016/j.matdes.2024.112929.
[93] L. Han, Z. Sun, W. Xia, S. Tsai, X. Zhang, J. Rao, et al., Thermodynamics-Guided
High-Throughput Discovery of Eutectic High-Entropy Alloys for Rapid
Solidification, pp. 2401559-1–9, Adv. Sci. (2024), https://doi.org/10.1002/
advs.202401559.
[94] Clyne, T. The influence of composition on solidification cracking susceptibility in
binary alloy systems, 1981. 74(4): pp. 65–73.
[95] S. Kou, A criterion for cracking during solidification, Acta Mater. 88 (2015)
366–374, https://doi.org/10.1016/j.actamat.2015.01.034.
[96] G. Tang, B.J. Gould, A. Ngowe, A.D. Rollett, An updated index including
toughness for hot-cracking susceptibility, Metall. Mater. Trans. A 53 (4) (2022)
1486–1498, https://doi.org/10.1007/s11661-022-06612-6.
[97] W. Kurz, B. Giovanola, R. Trivedi, Theory of microstructural development during
rapid solidification, Acta Metall. 34 (5) (1986) 823–830, https://doi.org/
10.1016/0001-6160(86)90056-8.
[98] B. Rankouhi, A.K. Agrawal, F.E. Pfefferkorn, D.J. Thoma, A dimensionless
number for predicting universal processing parameter boundaries in metal
powder bed additive manufacturing, Manuf. Lett. 27 (2021) 13–17, https://doi.
org/10.1016/j.mfglet.2020.12.002.
[99] S. Sheikh, B. Vela, V. Attari, X. Huang, P. Morcos, J. Hanagan, et al., Exploring
chemistry and additive manufacturing design spaces: a perspective on
computationally-guided design of printable alloys, Mater. Res. Lett. 12 (4) (2024)
235–263, https://doi.org/10.1080/21663831.2024.2316204.
[100] M.J. Abere, E. Ziade, P. Lu, C.B. Saltonstall, X. Gu, W.J. Wright, et al., A predictive
analytical model of thermal conductivity for aluminum/transition metal highentropy alloys, pp. 114330-1–5, Scr. Mater. 208 (2022), https://doi.org/
10.1016/j.scriptamat.2021.114330.
[101] D. King, S. Middleburgh, A. McGregor, M. Cortie, Predicting the formation and
stability of single phase high-entropy alloys, Acta Mater. 104 (2016) 172–179,
https://doi.org/10.1016/j.actamat.2015.11.040.
[102] Y.-C. Yang, C. Liu, C.-Y. Lin, Z. Xia, Core effect of local atomic configuration and
design principles in AlxCoCrFeNi high-entropy alloys, Scr. Mater. 178 (2020)
181–186, https://doi.org/10.1016/j.scriptamat.2019.11.016.
[103] P. Sarswat, T. Smith, S. Sarkar, A. Murali, M. Free, Design and Fabrication of New
High Entropy Alloys for Evaluating Titanium Replacements in Additive
Manufacturing, pp. 3001-1–37, Mater. (Basel) 13 (13) (2020), https://doi.org/
10.3390/ma13133001.
[104] E.P. George, D. Raabe, R.O. Ritchie, High-entropy alloys, Nat. Rev. Mater. 4 (8)
(2019) 515–534, https://doi.org/10.1038/s41578-019-0121-4.
[105] Y. Peng, Y. Kong, W. Zhang, M. Zhang, H. Wang, Effect of diffusion barrier and
interfacial strengthening on the interface behavior between high entropy alloy
and diamond, pp. 157023-1–11, J. Alloy. Compd. 852 (2021), https://doi.org/
10.1016/j.jallcom.2020.157023.
[106] T. Zuo, M.C. Gao, L. Ouyang, X. Yang, Y. Cheng, R. Feng, et al., Tailoring
magnetic behavior of CoFeMnNiX (X= Al, Cr, Ga, and Sn) high entropy alloys by
metal doping, Acta Mater. 130 (2017) 10–18, https://doi.org/10.1016/j.
actamat.2017.03.013.
[107] T. Saelee, S. Boonchuay, A. Sriwattana, M. Rittiruam, P. Khajondetchairit,
S. Praserthdam, et al., On the enhanced performance of Pt-based high-entropy
alloys catalyst during water–gas shift reaction: A density functional theory study,
pp. 157023-1–, Appl. Surf. Sci. 623 (2023) https://doi.org/10.1016/j.
apsusc.2023.157023.
[108] S. Chen, Z.H. Aitken, S. Pattamatta, Z. Wu, Z.G. Yu, D.J. Srolovitz, et al.,
Simultaneously enhancing the ultimate strength and ductility of high-entropy
alloys via short-range ordering, Nat. Commun. 12 (1) (2021) 1–11, https://doi.
org/10.1038/s41467-021-25264-5.
[109] A. Jarlöv, W. Ji, Z. Zhu, Y. Tian, R. Babicheva, R. An, et al., Molecular dynamics
study on the strengthening mechanisms of Cr-Fe-Co-Ni high-entropy alloys based
on the generalized stacking fault energy, pp. 164137-1–11, J. Alloy. Compd. 905
(2022), https://doi.org/10.1016/j.jallcom.2022.164137.
[110] P. Niu, R. Li, K. Gan, Z. Fan, T. Yuan, C. Han, Manipulating stacking fault energy
to achieve crack inhibition and superior strength–ductility synergy in an
additively manufactured high-entropy alloy, pp. 2310160-1–11, Adv. Mater.
(2024), https://doi.org/10.1002/adma.202310160.
39
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
[111] A. Jarlöv, W. Ji, R. Babicheva, Y. Tian, Z. Hu, H.L. Seet, et al., Tailoring shortrange order and dislocation evolution in Cr–Co–Ni medium-entropy alloys: A
molecular dynamics study, pp. 112840-1–12, Mater. Des. 24 (2024), https://doi.
org/10.1016/j.matdes.2024.112840.
[112] J. Wang, H. Kwon, H.S. Kim, B.-J. Lee, A neural network model for high entropy
alloy design, pp. 60-1–13, npj Comput. Mater. 9 (1) (2023), https://doi.org/
10.1038/s41524-023-01010-x.
[113] D. Raabe, J.R. Mianroodi, J. Neugebauer, Accelerating the design of
compositionally complex materials via physics-informed artificial intelligence,
Nat. Comput. Sci. 3 (3) (2023) 198–209, https://doi.org/10.1038/s43588-02300412-7.
[114] Z. Pei, J. Yin, P.K. Liaw, D. Raabe, Toward the design of ultrahigh-entropy alloys
via mining six million texts, pp. 54-1–8, Nat. Commun. 14 (1) (2023), https://doi.
org/10.1038/s41467-022-35766-5.
[115] R. Duan, J. Xu, Y. Zhao, Q. Zhou, Z. Yan, Y. Xie, et al., High entropy alloys
amenable for laser powder bed fusion: a thermodynamics guided machine
learning search, pp. 104195-1–17, Addit. Manuf. 86 (2024), https://doi.org/
10.1016/j.addma.2024.104195.
[116] B. Zhang, R. Seede, L. Xue, K.C. Atli, C. Zhang, A. Whitt, et al., An efficient
framework for printability assessment in Laser Powder Bed Fusion metal additive
manufacturing, pp. 102018-1–17, Addit. Manuf. 46 (2021), https://doi.org/
10.1016/j.addma.2021.102018.
[117] C. Zhang, L. Xue, S.A. Pestka, M. Ranaiefar, K.C. Atli, P. Honarmandi, et al.,
Processing parameters and martensitic phase transformation relationships in near
defect-free additively manufactured NiTiHf high temperature shape memory
alloys, pp. 110988-1–19, Mater. Des. 222 (2022), https://doi.org/10.1016/j.
matdes.2022.110988.
[118] Y. Li, L. Chen, L. Lu, X. Zhang, W. Zhou, X. Ren, Numerical and experimental
study of RHEAs surface morphology and defect in selective laser melting, pp.
106484-1–12, Int. J. Refract. Met. Hard Mater. 118 (2024), https://doi.org/
10.1016/j.matdes.2024.112929.
[119] H. Zhang, W. Xu, Y. Xu, Z. Lu, D. Li, The thermal-mechanical behavior of
WTaMoNb high-entropy alloy via selective laser melting (SLM): experiment and
simulation, Int. J. Adv. Manuf. Technol. 96 (2018) 461–474, https://doi.org/
10.1007/s00170-017-1331-9.
[120] H. Li, S. Thomas, C. Hutchinson, Delivering microstructural complexity to
additively manufactured metals through controlled mesoscale chemical
heterogeneity, pp. 117637-1–14, Acta Mater. 226 (2022), https://doi.org/
10.1016/j.actamat.2022.117637.
[121] H. Li, E.G. Brodie, C. Hutchinson, Predicting the chemical homogeneity in laser
powder bed fusion (LPBF) of mixed powders after remelting, pp. 103447-1–15,
Addit. Manuf. 65 (2023), https://doi.org/10.1016/j.addma.2023.103447.
[122] Y. Zhu, K. Zhang, Z. Meng, K. Zhang, P. Hodgson, N. Birbilis, et al., Ultrastrong
nanotwinned titanium alloys through additive manufacturing, Nat. Mater. 21 (11)
(2022) 1–5, https://doi.org/10.1038/s41563-022-01359-2.
[123] S. Kurian, R. Mirzaeifar, Selective laser melting of aluminum nano-powder
particles, a molecular dynamics study, pp. 101272-1–14, Addit. Manuf. 35
(2020), https://doi.org/10.1016/j.addma.2020.101272-1–14.
[124] S. Liu, B.B. Kappes, B. Amin-ahmadi, O. Benafan, X. Zhang, A.P. Stebner, Physicsinformed machine learning for composition–process–property design: Shape
memory alloy demonstration, pp. 100898-1–12, Appl. Mater. Today 22 (2021),
https://doi.org/10.1016/j.apmt.2020.100898.
[125] Y.-K. Kim, S. Yang, K.-A. Lee, Compressive creep behavior of selective laser
melted CoCrFeMnNi high-entropy alloy strengthened by in-situ formation of
nano-oxides, pp. 101543-1–12, Addit. Manuf. 36 (2020), https://doi.org/
10.1016/j.addma.2020.101543.
[126] D. Yim, M.J. Jang, J.W. Bae, J. Moon, C.-H. Lee, S.-J. Hong, et al., Compaction
behavior of water-atomized CoCrFeMnNi high-entropy alloy powders, Mater.
Chem. Phys. 210 (2018) 95–102, https://doi.org/10.1016/j.
matchemphys.2017.06.013.
[127] B. Wang, B. Lu, L. Zhang, J. Zhang, B. Li, Q. Ji, et al., Rapid in situ alloying of
CoCrFeMnNi high-entropy alloy from elemental feedstock toward highthroughput synthesis via laser powder bed fusion, Front. Mech. Eng. 18 (1) (2023)
11, https://doi.org/10.1007/s11465-022-0727-x.
[128] Y. Guo, H. Su, P. Yang, Z. Shen, D. Zhao, Y. Zhao, et al., New insight into
tailorable eutectic high entropy alloys with remarkable strength–ductility synergy
and ample shaping freedom fabricated using laser powder bed fusion, pp.
103257-1–18, Addit. Manuf. 60 (2022), https://doi.org/10.1016/j.
addma.2022.103257.
[129] Y. Guo, H. Su, H. Zhou, Z. Shen, Y. Liu, J. Zhang, et al., Unique strength-ductility
balance of AlCoCrFeNi2. 1 eutectic high entropy alloy with ultra-fine duplex
microstructure prepared by selective laser melting, J. Mater. Sci. Technol. 111
(2022) 298–306, https://doi.org/10.1016/j.jmst.2021.10.013.
[130] X. Sun, M. Chen, T. Liu, K. Zhang, H. Wei, Z. Zhu, et al., Characterization,
preparation, and reuse of metallic powders for laser powder bed fusion: a review,
pp. 012003-1–40, Int. J. Extrem. Manuf. 6 (2023), https://doi.org/10.1088/
2631-7990/acfbc3.
[131] A. Kumar, A. Singh, A. Suhane, Mechanically alloyed high entropy alloys: existing
challenges and opportunities, J. Mater. Res. Technol. 17 (2022) 2431–2456,
https://doi.org/10.1016/j.jmrt.2022.01.141.
[132] P. Zhou, D. Xiao, Z. Wu, X. Ou, Al0. 5FeCoCrNi high entropy alloy prepared by
selective laser melting with gas-atomized pre-alloy powders, Mater. Sci. Eng.: A
739 (2019) 86–89, https://doi.org/10.1016/j.msea.2018.10.035.
[133] Z. Geng, C. Chen, R. Li, J. Luo, K. Zhou, Composition inhomogeneity reduces
cracking susceptibility in additively manufactured AlCoCrFeNi2. 1 eutectic high-
entropy alloy produced by laser powder bed fusion, pp. 102941-1–14, Addit.
Manuf. 56 (2022), https://doi.org/10.1016/j.addma.2022.102941.
[134] T. Smith, A. Thompson, T. Gabb, C. Bowman, C. Kantzos, Efficient production of a
high-performance dispersion strengthened, multi-principal element alloy, Sci.
Rep. 10 (1) (2020) 1–9, https://doi.org/10.1038/s41598-020-66436-5.
[135] A. Chesetti, S. Banerjee, S. Dasari, M.S.K. Nartu, S. Varahabhatla, A. Sharma, et
al., 3D printable low density B2+ BCC refractory element based complex
concentrated alloy with high compressive strength and plasticity, pp. 1151601–9, Scr. Mater. 225 (2023), https://doi.org/10.1016/j.scriptamat.2022.115160.
[136] F. Wang, T. Yuan, R. Li, S. Lin, Z. Xie, L. Li, et al., Comparative study on
microstructures and mechanical properties of ultra ductility single-phase
Nb40Ti40Ta20 refractory medium entropy alloy by selective laser melting and
vacuum arc melting, pp. 169065-1–15, J. Alloy. Compd. 942 (2023), https://doi.
org/10.1016/j.jallcom.2023.169065.
[137] P. Gu, T. Qi, L. Chen, T. Ge, X. Ren, Manufacturing and analysis of VNbMoTaW
refractory high-entropy alloy fabricated by selective laser melting, pp. 1058341–10, Int. J. Refract. Met. Hard Mater. 105 (2022), https://doi.org/10.1016/j.
ijrmhm.2022.105834.
[138] N. Razumov, T.Y. Makhmutov, A. Kim, I. Goncharov, N. Ozerskoi, A. Silin, et al.,
Structure and Properties of Ti–Zr–Ni–Co–Cu High-Entropy Alloy After Powder
Bed Fusion of Powders Produced by Mechanical Alloying and Plasma
Spheroidization, Trans. Indian Inst. Met. 75 (10) (2022) 1–10, https://doi.org/
10.1007/s12666-022-02616-3.
[139] Y. Nie, J. Tang, B. Yang, Q. Lei, S. Yu, Y. Li, Comparison in characteristic and
atomization behavior of metallic powders produced by plasma rotating electrode
process, Adv. Powder Technol. 31 (5) (2020) 2152–2160, https://doi.org/
10.1016/j.apt.2020.03.006.
[140] C. Liu, K. Zhu, W. Ding, Y. Liu, G. Chen, X. Qu, Additive manufacturing of
WMoTaTi refractory high-entropy alloy by employing fluidised powders, Powder
Metall. 65 (5) (2022) 413–425, https://doi.org/10.1080/
00325899.2022.2031718.
[141] S. Mooraj, G. Kim, X. Fan, S. Samuha, Y. Xie, T. Li, et al., Additive manufacturing
of defect-free TiZrNbTa refractory high-entropy alloy with enhanced elastic
isotropy via in-situ alloying of elemental powders, pp. 14-1–12, Commun. Mater.
5 (1) (2024), https://doi.org/10.1038/s43246-024-00452-0.
[142] Y. Kuzminova, D. Firsov, A. Dudin, S. Sergeev, A. Zhilyaev, A. Dyakov, et al., The
effect of the parameters of the powder bed fusion process on the microstructure
and mechanical properties of CrFeCoNi medium-entropy alloys, pp. 106651-1–8,
Intermetallics 116 (2020), https://doi.org/10.1016/j.intermet.2019.106651.
[143] R. Li, P. Niu, T. Yuan, P. Cao, C. Chen, K. Zhou, Selective laser melting of an
equiatomic CoCrFeMnNi high-entropy alloy: Processability, non-equilibrium
microstructure and mechanical property, J. Alloy. Compd. 746 (2018) 125–134,
https://doi.org/10.1016/j.jallcom.2018.02.298.
[144] G.H. Aylward, T.J.V. Findlay, SI chemical data, Wiley, New York, 1973.
[145] J. Ge, C. Chen, R. Zhao, Q. Liu, Y. Long, J. Wang, et al., Strength-ductility synergy
of CoCrNi medium-entropy alloy processed with laser powder bed fusion, pp.
110774-1–14, Mater. Des. 219 (2022), https://doi.org/10.1016/j.
matdes.2022.110774.
[146] M. Jin, E. Hosseini, S.R. Holdsworth, M.-S. Pham, Thermally activated
dependence of fatigue behaviour of CrMnFeCoNi high entropy alloy fabricated by
laser powder-bed fusion, pp. 102600-1–13, Addit. Manuf. 51 (2022), https://doi.
org/10.1016/j.addma.2022.102600.
[147] Z. Zhu, Q. Nguyen, F. Ng, X. An, X. Liao, P. Liaw, et al., Hierarchical
microstructure and strengthening mechanisms of a CoCrFeNiMn high entropy
alloy additively manufactured by selective laser melting, Scr. Mater. 154 (2018)
20–24, https://doi.org/10.1016/j.matdes.2022.110774.
[148] D. Lin, L. Xu, H. Jing, Y. Han, L. Zhao, Y. Zhang, et al., A strong, ductile, highentropy FeCoCrNi alloy with fine grains fabricated via additive manufacturing
and a single cold deformation and annealing cycle, pp. 101591-1–12, Addit.
Manuf. 36 (2020), https://doi.org/10.1016/j.addma.2020.101591.
[149] J. Wang, J. Zou, H. Yang, L. Zhang, Z. Liu, X. Dong, et al., Exceptional strengthductility synergy of additively manufactured CoCrNi medium-entropy alloy
achieved by lattice defects in heterogeneous microstructures, J. Mater. Sci.
Technol. 10 (2022) 1–8, https://doi.org/10.1016/j.jmst.2022.03.024.
[150] H. Duan, B. Liu, A. Fu, J. He, T. Yang, C.T. Liu, et al., Segregation enabled
outstanding combination of mechanical and corrosion properties in a FeCrNi
medium entropy alloy manufactured by selective laser melting, J. Mater. Sci.
Technol. 99 (2022) 207–214, https://doi.org/10.1016/j.jmst.2021.05.018.
[151] P. Niu, R. Li, T. Yuan, S. Zhu, C. Chen, M. Wang, et al., Microstructures and
properties of an equimolar AlCoCrFeNi high entropy alloy printed by selective
laser melting, Intermetallics 104 (2019) 24–32, https://doi.org/10.1016/j.
intermet.2018.10.018.
[152] H.Y. Jung, N.J. Peter, E. Gärtner, G. Dehm, V. Uhlenwinkel, E.A. Jägle, Bulk
nanostructured AlCoCrFeMnNi chemically complex alloy synthesized by laserpowder bed fusion, pp. 101337-1–8, Addit. Manuf. 35 (2020), https://doi.org/
10.1016/j.addma.2020.101337.
[153] H. Jung, J. Lee, G.H. Gu, H. Lee, S.-M. Seo, A. Zargaran, et al., Multiscale defects
enable synergetic improvement in yield strength of CrCoNi-based mediumentropy alloy fabricated via laser-powder bed fusion, pp. 103360-1–15, Addit.
Manuf. 61 (2022), https://doi.org/10.1016/j.addma.2022.103360.
[154] Z. Jian, J. Fan, P. Yong, Y. Dongqing, W. Kehong, Microstructures and properties
of AlCoCrFeNi2. 5 eutectic high entropy alloy fabricated by selective laser
melting, pp. 145081-1–11, Mater. Sci. Eng.: A 875 (2023), https://doi.org/
10.1016/j.msea.2023.145081.
[155] Z. Geng, C. Chen, M. Song, J. Luo, J. Chen, R. Li, et al., High strength Al0.
7CoCrFeNi2.4 hypereutectic high entropy alloy fabricated by laser powder bed
40
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
fusion via triple-nanoprecipitation, J. Mater. Sci. Technol. 187 (2024) 141–155,
https://doi.org/10.1016/j.jmst.2023.11.054.
[156] S. Luo, Z. Wang, H. Nagaumi, Z. Wu, Tailoring the microstructure and mechanical
property of additively manufactured AlCrCuFeNi3. 0 high-entropy alloy through
heat treatment, pp. 143192-1–13, Mater. Sci. Eng.: A 844 (2022), https://doi.org/
10.1016/j.msea.2022.143192.
[157] F. Yang, L. Wang, Z. Wang, Q. Wu, K. Zhou, X. Lin, et al., Ultra strong and ductile
eutectic high entropy alloy fabricated by selective laser melting, J. Mater. Sci.
Technol. 106 (2022) 128–132, https://doi.org/10.1016/j.jmst.2021.08.015.
[158] Y. Wu, X. Zhao, Q. Chen, C. Yang, M. Jiang, C. Liu, et al., Strengthening and
fracture mechanisms of a precipitation hardening high-entropy alloy fabricated
by selective laser melting, Virtual Phys. Prototyp. 17 (3) (2022) 1–17, https://doi.
org/10.1080/17452759.2022.2037055.
[159] L. Xu, Y. Jia, S. Wu, Y. Jia, K. Song, G. Wang, Multiscale crack deflection
overcomes intermediate-temperature brittleness via hierarchical fiber-like
structure in a dual nanoprecipitation-strengthened high-entropy alloy fabricated
by selective laser melting, pp. 115189-1–8, Scr. Mater. 225 (2023), https://doi.
org/10.1016/j.scriptamat.2022.115189.
[160] W.-C. Lin, Y.-J. Chang, T.-H. Hsu, S. Gorsse, F. Sun, T. Furuhara, et al.,
Microstructure and tensile property of a precipitation strengthened high entropy
alloy processed by selective laser melting and post heat treatment, pp. 1016011–10, Addit. Manuf. 36 (2020), https://doi.org/10.1016/j.addma.2020.101601.
[161] J. Feng, D. Wei, P. Zhang, Z. Yu, C. Liu, W. Lu, et al., Preparation of TiNbTaZrMo
high-entropy alloy with tunable Young’s modulus by selective laser melting,
J. Manuf. Process. 85 (2023) 160–165, https://doi.org/10.1016/j.
jmapro.2022.11.046.
[162] P. Agrawal, R.S. Haridas, S. Thapliyal, S. Yadav, R.S. Mishra, B.A. McWilliams, et
al., Metastable high entropy alloys: An excellent defect tolerant material for
additive manufacturing, pp. 142005-1–11, Mater. Sci. Eng.: A 826 (2021),
https://doi.org/10.1016/j.msea.2021.142005.
[163] C. Tian, D. Ouyang, P. Wang, L. Zhang, C. Cai, K. Zhou, et al., Strength-ductility
synergy of an additively manufactured metastable high-entropy alloy achieved by
transformation-induced plasticity strengthening, pp. 103823-1–14, Int. J. Plast.
172 (2024), https://doi.org/10.1016/j.ijplas.2023.103823.
[164] J.M. Park, J. Choe, H.K. Park, S. Son, J. Jung, T.-S. Kim, et al., Synergetic
strengthening of additively manufactured (CoCrFeMnNi) 99C1 high-entropy alloy
by heterogeneous anisotropic microstructure, pp. 101333-1–15, Addit. Manuf. 35
(2020), https://doi.org/10.1016/j.addma.2020.101333.
[165] D. Zhao, Q. Yang, D. Wang, M. Yan, P. Wang, M. Jiang, et al., Ordered nitrogen
complexes overcoming strength–ductility trade-off in an additively manufactured
high-entropy alloy, Virtual Phys. Prototyp. 15 (sup1) (2020) 532–542, https://
doi.org/10.1080/17452759.2020.1840783.
[166] J. Xu, R. Duan, K. Feng, C. Zhang, Q. Zhou, P. Liu, et al., Enhanced strength and
ductility of laser powder bed fused NbMoTaW refractory high-entropy alloy via
carbon microalloying, pp. 100079-1–6, Addit. Manuf. Lett. 3 (2022), https://doi.
org/10.1016/j.addlet.2022.100079.
[167] H. Chen, et al., Hierarchical microstructures and strengthening mechanisms of
nano-TiC reinforced CoCrFeMnNi high-entropy alloy composites prepared by
laser powder bed fusion, J. Mater. Sci. Technol. 136 (2023) 245–259, https://doi.
org/10.1016/j.jmst.2022.06.053.
[168] Y.-K. Kim, J.-E. Ahn, Y. Song, H. Choi, S. Yang, K.-A. Lee, Selective laser melted
CrMnFeCoNi+ 3 wt% Y2O3 high-entropy alloy matrix nanocomposite:
Fabrication, microstructure and nanoindentation properties, pp. 107319-1–5,
Intermetallics 138 (2021), https://doi.org/10.1016/j.intermet.2021.107319.
[169] L. Chen, et al., Effect of TiC on the high-temperature oxidation behavior of
WMoTaNbV refractory high entropy alloy fabricated by selective laser melting,
pp. 106027-1–15, Int. J. Refract. Met. Hard Mater. 110 (2022), https://doi.org/
10.1016/j.ijrmhm.2022.106027.
[170] Y. Lu, Y. Dong, S. Guo, L. Jiang, H. Kang, T. Wang, et al., A promising new class of
high-temperature alloys: eutectic high-entropy alloys, Sci. Rep. 4 (1) (2014) 1–5,
https://doi.org/10.1038/srep06200.
[171] D.M. Stefanescu, Science and engineering of casting solidification, Springer, New
York, 2015. ISBN: 978-3-319-15692-7.
[172] S.P. Murray, K.M. Pusch, A.T. Polonsky, C.J. Torbet, G.G. Seward, N. Zhou, et al.,
A defect-resistant Co–Ni superalloy for 3D printing, Nat. Commun. 11 (1) (2020)
1–11, https://doi.org/10.1038/s41467-020-18775-0.
[173] L.-X. Liu, J. Pan, C. Zhang, J.-Y. Xu, R. Guo, L. Liu, Achieving high strength and
ductility in a 3D-printed high entropy alloy by cooperative planar slipping and
stacking fault, pp. 143106-1–8, Mater. Sci. Eng.: A 843 (2022), https://doi.org/
10.1016/j.msea.2022.143106.
[174] H. Yao, Z. Tan, D. He, Z. Zhou, Z. Zhou, Y. Xue, et al., High strength and ductility
AlCrFeNiV high entropy alloy with hierarchically heterogeneous microstructure
prepared by selective laser melting, pp. 152196-1–8, J. Alloy. Compd. 813
(2020), https://doi.org/10.1016/j.jallcom.2019.152196.
[175] K. Kwak, Y. Okamura, Y. Mine, K. Takashima, S. Koseki, S. Ando, et al., Micromechanical characterisation of slip behaviour and precipitation strengthening in
CoCrFeNiTiMo alloy additively manufactured by laser powder bed fusion, pp.
142970-1–7, Mater. Sci. Eng.: A 840 (2022), https://doi.org/10.1016/j.
msea.2022.142970.
[176] W. Xu, E.W. Lui, A. Pateras, M. Qian, M. Brandt, In situ tailoring microstructure in
additively manufactured Ti-6Al-4V for superior mechanical performance, Acta
Mater. 125 (2017) 390–400, https://doi.org/10.1016/j.actamat.2016.12.027.
[177] Y. Zhao, H. Zhang, J. Cai, X. Sun, L. Wang, X. Xu, et al., An efficient pores
suppression process design method for high strength BCC high entropy alloys via
powder bed fusion, J. Manuf. Process. 101 (2023) 371–385, https://doi.org/
10.1016/j.jmapro.2023.05.097.
[178] Y. Zhang, Y. Fang, M.-K. Kim, Z. Duan, Q. Yuan, E. Oh, et al., In-situ TiCxNy
nanoparticle reinforced crack-free CoCrFeNi medium-entropy alloy matrix
nanocomposites with high strength and ductility via laser powder bed fusion, pp.
111237-1–20, Compos. Part B: Eng. 273 (2024), https://doi.org/10.1016/j.
compositesb.2024.111237.
[179] L. Guo, J. Gu, B. Gan, S. Ni, Z. Bi, Z. Wang, et al., Effects of elemental segregation
and scanning strategy on the mechanical properties and hot cracking of a
selective laser melted FeCoCrNiMn-(N, Si) high entropy alloy, pp. 158892-1–12,
J. Alloy. Compd. 865 (2021), https://doi.org/10.1016/j.jallcom.2021.158892.
[180] M. Jin, A. Piglione, B. Dovgyy, E. Hosseini, P.A. Hooper, S.R. Holdsworth, et al.,
Cyclic plasticity and fatigue damage of CrMnFeCoNi high entropy alloy fabricated
by laser powder-bed fusion, pp. 101584-1–15, Addit. Manuf. 36 (2020), https://
doi.org/10.1016/j.addma.2020.101584.
[181] H. Wang, Z. Zhu, H. Chen, A. Wang, J. Liu, H. Liu, et al., Effect of cyclic rapid
thermal loadings on the microstructural evolution of a CrMnFeCoNi high-entropy
alloy manufactured by selective laser melting, Acta Mater. 196 (2020) 609–625,
https://doi.org/10.1016/j.actamat.2020.07.006.
[182] A. Piglione, B. Dovgyy, C. Liu, C. Gourlay, P. Hooper, M. Pham, Printability and
microstructure of the CoCrFeMnNi high-entropy alloy fabricated by laser powder
bed fusion, Mater. Lett. 224 (2018) 22–25, https://doi.org/10.1016/j.
matlet.2018.04.052.
[183] Z. Xu, H. Zhang, W. Li, A. Mao, L. Wang, G. Song, et al., Microstructure and
nanoindentation creep behavior of CoCrFeMnNi high-entropy alloy fabricated by
selective laser melting, Addit. Manuf. 28 (2019) 766–771, https://doi.org/
10.1016/j.addma.2019.06.012.
[184] R. Savinov, Y. Wang, J. Wang, J. Shi, Comparison of microstructure and
properties of CoCrFeMnNi high-entropy alloy from selective laser melting and
directed energy deposition processes, Procedia Manuf. 53 (2021) 435–442,
https://doi.org/10.1016/j.promfg.2021.06.046.
[185] X. He, H. Wang, Z. Zhu, L. Wang, J. Liu, N. Haghdadi, et al., Texture evolution in a
CrMnFeCoNi high-entropy alloy manufactured by laser powder bed fusion,
J. Mater. Sci. 57 (21) (2022) 1–12, https://doi.org/10.1007/s10853-022-07025x.
[186] C. Zhang, K. Feng, H. Kokawa, B. Han, Z. Li, Cracking mechanism and mechanical
properties of selective laser melted CoCrFeMnNi high entropy alloy using
different scanning strategies, pp. 139672-1–11, Mater. Sci. Eng.: A 789 (2020),
https://doi.org/10.1016/j.msea.2020.139672.
[187] S. Kou, Welding metallurgy, John Wiley & Sons, New Jersey, USA, 2003. ISBN: 0471-43491-4.
[188] P. Niu, R. Li, S. Zhu, M. Wang, C. Chen, T. Yuan, Hot cracking, crystal orientation
and compressive strength of an equimolar CoCrFeMnNi high-entropy alloy
printed by selective laser melting, pp. 106147-1–8, Opt. Laser Technol. 127
(2020), https://doi.org/10.1016/j.optlastec.2020.106147.
[189] Y. Peng, C. Jia, L. Song, Y. Bian, H. Tang, G. Cai, et al., The manufacturing process
optimization and the mechanical properties of FeCoCrNi high entropy alloys
fabricated by selective laser melting, pp. 107557-1–9, Intermetallics 145 (2022),
https://doi.org/10.1016/j.intermet.2022.107557.
[190] X. Yang, Y. Ge, J. Lehtonen, S.-P. Hannula, Hierarchical microstructure of laser
powder bed fusion produced face-centered-cubic-structured equiatomic
CrFeNiMn multicomponent alloy, pp. 4498-1–11, Materials 13 (20) (2020),
https://doi.org/10.3390/ma13204498.
[191] P. Kumar, S. Huang, D.H. Cook, K. Chen, U. Ramamurty, X. Tan, et al., A strong
fracture-resistant high-entropy alloy with nano-bridged honeycomb
microstructure intrinsically toughened by 3D-printing, pp. 841-1–9, Nat.
Commun. 15 (2024), https://doi.org/10.1038/s41467-024-45178-2.
[192] D. Karlsson, A. Marshal, F. Johansson, M. Schuisky, M. Sahlberg, J.M. Schneider,
et al., Elemental segregation in an AlCoCrFeNi high-entropy alloy–A comparison
between selective laser melting and induction melting, J. Alloy. Compd. 784
(2019) 195–203, https://doi.org/10.1016/j.jallcom.2018.12.267.
[193] D. Vogiatzief, A. Evirgen, S. Gein, V.R. Molina, A. Weisheit, M. Pedersen, Laser
Powder Bed Fusion and Heat Treatment of an AlCrFe2Ni2 High Entropy Alloy, pp.
248-1–12, Front. Mater. 7 (2020), https://doi.org/10.3389/fmats.2020.00248.
[194] T. Han, Y. Liu, D. Yang, N. Qu, M. Liao, Z. Lai, et al., Effect of annealing on
microstructure and mechanical properties of AlCrFe2Ni2 medium entropy alloy
fabricated by laser powder bed fusion additive manufacturing, pp. 142868-1–14,
Mater. Sci. Eng.: A 839 (2022), https://doi.org/10.1016/j.msea.2022.142868.
[195] Y. Wang, R. Li, P. Niu, Z. Zhang, T. Yuan, J. Yuan, et al., Microstructures and
properties of equimolar AlCoCrCuFeNi high-entropy alloy additively
manufactured by selective laser melting, pp. 106746-1–10, Intermetallics 120
(2020), https://doi.org/10.1016/j.intermet.2020.106746.
[196] M. Zhang, X. Zhou, D. Wang, W. Zhu, J. Li, Y.F. Zhao, AlCoCuFeNi high-entropy
alloy with tailored microstructure and outstanding compressive properties
fabricated via selective laser melting with heat treatment, Mater. Sci. Eng.: A 743
(2019) 773–784, https://doi.org/10.1016/j.msea.2018.11.118.
[197] S. Luo, P. Gao, H. Yu, J. Yang, Z. Wang, X. Zeng, Selective laser melting of an
equiatomic AlCrCuFeNi high-entropy alloy: Processability, non-equilibrium
microstructure and mechanical behavior, J. Alloy. Compd. 771 (2019) 387–397,
https://doi.org/10.1016/j.jallcom.2018.08.290.
[198] B. Yuan, C. Li, Y. Dong, Y. Yang, P. Zhang, Z. Zhang, Selective laser melting of the
Al0. 3CoCrFeNiCu high-entropy alloy: Processing parameters, microstructure and
mechanical properties, pp. 110847-1–15, Mater. Des. 220 (2022), https://doi.
org/10.1016/j.matdes.2022.110847.
[199] M. Jia, D. Liang, Q. Du, H. Wang, Y. Wu, S. Jiang, et al., Fe-Co-Ni-Cu high entropy
magnetic nanoparticles with high magnetothermal properties, pp. 116119-1–6,
Scr. Mater. 247 (2024), https://doi.org/10.1016/j.scriptamat.2024.116119.
41
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
[200] J. Gao, Y. Jin, Y. Fan, D. Xu, L. Meng, C. Wang, et al., Fabricating antibacterial
CoCrCuFeNi high-entropy alloy via selective laser melting and in-situ alloying,
J. Mater. Sci. Technol. 102 (2022) 159–165, https://doi.org/10.1016/j.
jmst.2021.07.002.
[201] Z. Rao, P.-Y. Tung, R. Xie, Y. Wei, H. Zhang, A. Ferrari, et al., Machine
learning–enabled high-entropy alloy discovery, Science 378 (6615) (2022)
78–85, https://doi.org/10.1126/science.abo4940.
[202] T. Fujieda, M. Chen, H. Shiratori, K. Kuwabara, K. Yamanaka, Y. Koizumi, et al.,
Mechanical and corrosion properties of CoCrFeNiTi-based high-entropy alloy
additive manufactured using selective laser melting, Addit. Manuf. 25 (2019)
412–420, https://doi.org/10.1016/j.addma.2018.10.023.
[203] L. Farquhar, G. Maddison, L. Hardwick, F. Livera, I. Todd, R. Goodall, In-Situ
Alloying of CoCrFeNiX High Entropy Alloys by Selective Laser Melting, pp. 4561–13, Metals 12 (3) (2022), https://doi.org/10.3390/met12030456.
[204] U. Hecht, A. Vayyala, P. Barriobero-Vila, N. Navaeilavasani, S. Gein, I. Cazic, et
al., Microstructure evolution in the hypo-eutectic alloy Al0. 75CrFeNi2. 1
manufactured by laser powder bed fusion and subsequent annealing, pp. 1443151–12, Mater. Sci. Eng.: A 862 (2023), https://doi.org/10.1016/j.
msea.2022.144315.
[205] X. Song, Z. Liu, P.K. Liaw, Y. Zhang, Microstructures and precipitation behaviors
of a hypoeutectic high-entropy alloy prepared by laser powder bed fusion, pp.
104171-1–13, Addit. Manuf. (2024), https://doi.org/10.1016/j.
addma.2024.104171.
[206] Y. Zhu, S. Zhou, Z. Xiong, Y.-J. Liang, Y. Xue, L. Wang, Enabling stronger eutectic
high-entropy alloys with larger ductility by 3D printed directional lamellae, pp.
101901-1–10, Addit. Manuf. 39 (2021), https://doi.org/10.1016/j.
addma.2021.101901.
[207] L. He, S. Wu, A. Dong, H. Tang, D. Du, G. Zhu, et al., Selective laser melting of
dense and crack-free AlCoCrFeNi2. 1 eutectic high entropy alloy: Synergizing
strength and ductility, J. Mater. Sci. Technol. 117 (2022) 133–145, https://doi.
org/10.1016/j.jmst.2021.11.049.
[208] S. Wang, Y. Li, D. Zhang, Y. Yang, S.M. Manladan, Z. Luo, Microstructure and
mechanical properties of high strength AlCoCrFeNi2. 1 eutectic high entropy
alloy prepared by selective laser melting (SLM), pp. 131511-1–4, Mater. Lett. 310
(2022), https://doi.org/10.1016/j.matlet.2021.131511.
[209] L. Lan, W. Wang, Z. Cui, X. Hao, D. Qiu, Anisotropy study of the microstructure
and properties of AlCoCrFeNi2. 1 eutectic high entropy alloy additively
manufactured by selective laser melting, J. Mater. Sci. Technol. 129 (2022)
228–239, https://doi.org/10.1016/j.jmst.2022.04.020.
[210] A. Nassar, A. Mullis, R. Cochrane, Z. Aslam, S. Micklethwaite, L. Cao, Rapid
solidification of AlCoCrFeNi2. 1 high-entropy alloy, J. Alloy. Compd. 900 (2022)
163350, https://doi.org/10.1016/j.jallcom.2021.163350.
[211] J. Wang, M. Zhang, H. Wang, Z. Li, X. Cheng, B. Zhang, et al., Mitigating hotcracking of laser melted CoCrFeNiMnTix high-entropy alloys, pp. 131771-1–4,
Mater. Lett. 1 (2022), https://doi.org/10.1016/j.matlet.2022.131771.
[212] S. Luo, C. Zhao, Y. Su, Q. Liu, Z. Wang, Selective laser melting of dual phase
AlCrCuFeNix high entropy alloys: Formability, heterogeneous microstructures
and deformation mechanisms, pp. 100925-1–10, Addit. Manuf. 31 (2020),
https://doi.org/10.1016/j.addma.2019.100925.
[213] Y. Su, S. Luo, Z. Wang, Microstructure evolution and cracking behaviors of
additively manufactured AlxCrCuFeNi2 high entropy alloys via selective laser
melting, pp. 155823-1–10, J. Alloy. Compd. 842 (2020), https://doi.org/
10.1016/j.jallcom.2020.155823.
[214] S. Luo, Y. Su, Z. Wang, Microstructural evolution and mechanisms in additively
manufactured AlCrCuFeNix complex concentrated alloys via selective laser
melting, pp. 159443-1–12, J. Alloy. Compd. 870 (2021), https://doi.org/
10.1016/j.jallcom.2021.159443.
[215] C. Biffi, J. Fiocchi, P. Bassani, A. Tuissi, Continuous wave vs pulsed wave laser
emission in selective laser melting of AlSi10Mg parts with industrial optimized
process parameters: Microstructure and mechanical behaviour, Addit. Manuf. 24
(2018) 639–646, https://doi.org/10.1016/j.addma.2018.10.021.
[216] W. Liu, T. Yang, C. Liu, Precipitation hardening in CoCrFeNi-based high entropy
alloys, Mater. Chem. Phys. 210 (2018) 2–11, https://doi.org/10.1016/j.
matchemphys.2017.07.037.
[217] P. Ji, Z. Wang, Y. Mu, Y. Jia, G. Wang, Microstructural evolution of (FeCoNi)
85.84 Al7. 07Ti7. 09 high-entropy alloy fabricated by an optimized selective laser
melting process, pp. 111326-1–10, Mater. Des. 224 (2022), https://doi.org/
10.1016/j.matdes.2022.111326.
[218] G. Qin, Q. Yu, K. Yu, Y. Fang, R. Chen, Z. Liang, et al., Strengthening complex
concentrated alloy without ductility loss by 3D printed high-density coherent
nanoparticles, pp. 103987-1–13, Int. J. Plast. 177 (2024), https://doi.org/
10.1016/j.ijplas.2024.103987.
[219] B. Yuan, Y. Dong, C. Li, Y. Yang, P. Zhang, Excellent strengthening effect of L12
precipitates on the selective laser melting Al0. 3CoCrFeNiCu high entropy alloy
via annealing treatment, pp. 130628-1–4, Mater. Lett. 304 (2021), https://doi.
org/10.1016/j.matlet.2021.130628.
[220] Z.-Y. Liu, X.-Y. Zhao, Y.-W. Wu, Q. Chen, B.-H. Yang, P. Wang, et al.,
Homogenization heat treatment for an additively manufactured precipitationhardening high-entropy alloy, Rare Met. 41 (8) (2022) 1–11, https://doi.org/
10.1007/s12598-022-01976-5.
[221] D.B. Miracle, M.H. Tsai, O.N. Senkov, V. Soni, R. Banerjee, Refractory high
entropy superalloys (RSAs), Scr. Mater. 187 (2020) 445–452, https://doi.org/
10.1016/j.scriptamat.2020.06.048.
[222] R. Feng, B. Feng, M.C. Gao, C. Zhang, J.C. Neuefeind, J.D. Poplawsky, et al.,
Superior High-Temperature Strength in a Supersaturated Refractory High-
Entropy Alloy, pp. 2102401-1–14, Adv. Mater. 33 (48) (2021), https://doi.org/
10.1002/adma.202102401.
[223] C. Liu, Y. Wang, Y. Zhang, L.-C. Zhang, L. Wang, Deformation mechanisms of
additively manufactured TiNbTaZrMo refractory high-entropy alloy: The role of
cellular structure, pp. 103884-1–12, Int. J. Plast. 173 (2024), https://doi.org/
10.1016/j.ijplas.2024.103884.
[224] O. Gokcekaya, T. Ishimoto, Y. Nishikawa, Y.S. Kim, A. Matsugaki, R. Ozasa, et al.,
Novel single crystalline-like non-equiatomic TiZrHfNbTaMo bio-high entropy
alloy (BioHEA) developed by laser powder bed fusion, Mater. Res. Lett. 11 (4)
(2023) 274–280, https://doi.org/10.1080/21663831.2022.2147406.
[225] Z.G. Zhu, X.H. An, W.J. Lu, Z.M. Li, F.L. Ng, X.Z. Liao, et al., Selective laser
melting enabling the hierarchically heterogeneous microstructure and excellent
mechanical properties in an interstitial solute strengthened high entropy alloy,
Mater. Res. Lett. 7 (11) (2019) 453–459, https://doi.org/10.1080/
21663831.2019.1650131.
[226] Y. Hou, T. Liu, D. He, Z. Li, L. Chen, H. Su, et al., Sustaining Strength-Ductility
Synergy of SLM Fe50Mn30Co10Cr10 Metastable High-Entropy Alloy by Si
Addition, pp. 107565-1–11, Intermetallics 145 (2022), https://doi.org/10.1016/
j.intermet.2022.107565.
[227] S. Thapliyal, P. Agrawal, P. Agrawal, S.S. Nene, R.S. Mishra, B.A. McWilliams, et
al., Segregation engineering of grain boundaries of a metastable Fe-Mn-Co-Cr-Si
high entropy alloy with laser-powder bed fusion additive manufacturing, pp.
117271-1–16, Acta Mater. 219 (2021), https://doi.org/10.1016/j.
actamat.2021.117271.
[228] Y. Hou, Z. Li, L. Chen, Z. Xiang, P. Dai, J. Chen, SLM Fe50Mn30Co10Cr10
metastable high entropy alloy with Al-Ti addition: Synergizing strength and
ductility, pp. 168830-1–12, J. Alloy. Compd. 941 (2023), https://doi.org/
10.1016/j.jallcom.2023.168830.
[229] X. Yang, L. Cheng, H. Peng, B. Qian, L. Yang, Y. Shi, et al., Development of Fe-MnSi-Cr-Ni shape memory alloy with ultrahigh mechanical properties and large
recovery strain by laser powder bed fusion, J. Mater. Sci. Technol. 150 (2023)
201–216, https://doi.org/10.1016/j.jmst.2022.11.046.
[230] I. Ferretto, A. Sharma, D. Kim, N. Della Ventura, X. Maeder, J. Michler, et al.,
Fabrication of FeMnSi-based shape memory alloy components with gradedmicrostructures by laser powder bed fusion, pp. 103835-1–24, Addit. Manuf. 78
(2023), https://doi.org/10.1016/j.addma.2023.103835.
[231] J.M. Park, E.S. Kim, H. Kwon, P. Sathiyamoorthi, K.T. Kim, J.-H. Yu, et al., Effect
of heat treatment on microstructural heterogeneity and mechanical properties of
1% C-CoCrFeMnNi alloy fabricated by selective laser melting, pp. 102283-1–13,
Addit. Manuf. 47 (2021), https://doi.org/10.1016/j.addma.2021.102283.
[232] Y.-K. Kim, J.-H. Yu, H.S. Kim, K.-A. Lee, In-situ carbide-reinforced CoCrFeMnNi
high-entropy alloy matrix nanocomposites manufactured by selective laser
melting: Carbon content effects on microstructure, mechanical properties, and
deformation mechanism, pp. 108638-1–13, Compos. Part B: Eng. 210 (2021),
https://doi.org/10.1016/j.compositesb.2021.108638.
[233] Y.-K. Kim, K.-A. Lee, Stabilized sub–grain and nano carbides–driven 1.2 GPa
grade ultra–strong CrMnFeCoNi high–entropy alloy additively manufactured by
laser powder bed fusion, J. Mater. Sci. Technol. 117 (2022) 8–22, https://doi.org/
10.1016/j.jmst.2021.12.010.
[234] W. Wu, R. Zhou, B. Wei, S. Ni, Y. Liu, M. Song, Nanosized precipitates and
dislocation networks reinforced C-containing CoCrFeNi high-entropy alloy
fabricated by selective laser melting, Mater. Charact. 144 (2018) 605–610,
https://doi.org/10.1016/j.matchar.2018.08.019.
[235] U. Kocks, H. Mecking, Physics and phenomenology of strain hardening: the FCC
case, Prog. Mater. Sci. 48 (3) (2003) 171–273, https://doi.org/10.1016/S00796425(02)00003-8.
[236] R. Zhou, Y. Liu, B. Liu, J. Li, Q. Fang, Precipitation behavior of selective laser
melted FeCoCrNiC0. 05 high entropy alloy, Intermetallics 106 (2019) 20–25,
https://doi.org/10.1016/j.intermet.2018.12.001.
[237] D.W. Kim, Influence of nitrogen-induced grain refinement on mechanical
properties of nitrogen alloyed type 316LN stainless steel, J. Nucl. Mater. 420 (1-3)
(2012) 473–478, https://doi.org/10.1016/j.jnucmat.2011.11.001.
[238] Y.-K. Kim, M.-S. Baek, S. Yang, K.-A. Lee, In-situ formed oxide enables
extraordinary high-cycle fatigue resistance in additively manufactured
CoCrFeMnNi high-entropy alloy, pp. 101832-1–10, Addit. Manuf. 38 (2021),
https://doi.org/10.1016/j.addma.2020.101832.
[239] P. Chen, C. Yang, S. Li, M.M. Attallah, M. Yan, In-situ alloyed, oxide-dispersionstrengthened CoCrFeMnNi high entropy alloy fabricated via laser powder bed
fusion, pp. 108966-1–9, Mater. Des. 194 (2020), https://doi.org/10.1016/j.
matdes.2020.108966.
[240] Y.-K. Kim, J. Choe, K.-A. Lee, Selective laser melted equiatomic CoCrFeMnNi
high-entropy alloy: microstructure, anisotropic mechanical response, and
multiple strengthening mechanism, J. Alloy. Compd. 805 (2019) 680–691,
https://doi.org/10.1016/j.jallcom.2019.07.106.
[241] Y. Chen, B. Li, B. Chen, F. Xuan, High-cycle fatigue induced twinning in CoCrFeNi
high-entropy alloy processed by laser powder bed fusion additive manufacturing,
pp. 103319-1–17, Addit. Manuf. 61 (2023), https://doi.org/10.1016/j.
addma.2022.103319.
[242] C. Oses, C. Toher, S. Curtarolo, High-entropy ceramics, Nat. Rev. Mater. 5 (4)
(2020) 295–309, https://doi.org/10.1038/s41578-019-0170-8.
[243] H. Chen, T. Lu, Y. Wang, Y. Liu, T. Shi, K.G. Prashanth, et al., Laser additive
manufacturing of nano-TiC particles reinforced CoCrFeMnNi high-entropy alloy
matrix composites with high strength and ductility, pp. 142512-1–16, Mater. Sci.
Eng.: A 833 (2022), https://doi.org/10.1016/j.msea.2021.142512.
[244] B. Li, L. Zhang, Y. Xu, Z. Liu, B. Qian, F. Xuan, Selective laser melting of
CoCrFeNiMn high entropy alloy powder modified with nano-TiN particles for
42
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
high-entropy alloy, J. Mater. Sci. Technol. 155 (2023) 211–226, https://doi.org/
10.1016/j.jmst.2022.12.074.
[267] K. Zhou, D. Cui, Z. Chai, Y. Zhang, Z. Yang, C. Zhu, et al., In-situ tailoring
microstructures to promote strength-ductility synergy in laser powder bed fusion
of NiCoCr medium-entropy alloy, pp. 103443-1–16, Addit. Manuf. 66 (2023),
https://doi.org/10.1016/j.addma.2023.103443.
[268] S. Yan, X. He, M. Krüger, Y. Li, Q. Jia, Additive manufacturing of a new nonequiatomic high-entropy alloy with exceptional strength-ductility synergy via insitu alloying, pp. 112676-1–11, Mater. Des. 238 (2024), https://doi.org/10.1016/
j.matdes.2024.112676.
[269] J. Hou, B. Qian, Z. Zhu, S. Zou, G. Li, Q. Zhu, et al., A mechanical strong yet
ductile CoCrNi/Cr2B composite enabled by in-situ formed borides during laser
powder bed fusion, pp. 111428-1–14, Compos. Part B: Eng. (2024), https://doi.
org/10.1016/j.compositesb.2024.111428.
[270] Y. Liu, J. Ren, S. Guan, C. Li, Y. Zhang, S. Muskeri, et al., Microstructure and
mechanical behavior of additively manufactured CoCrFeMnNi high-entropy
alloys: Laser directed energy deposition versus powder bed fusion, Acta Mater.
250 (2023). 〈https://doi-org.remotexs.ntu.edu.sg/10.1016/j.actamat.2023
.118884〉, pp. 118884-1–18.
[271] X. Tang, H. Zhang, Z. Zhu, P. Xue, L. Wu, F. Liu, et al., Dual-phase synergistic
deformation characteristics and strengthening mechanism of AlCoCrFeNi2. 1
eutectic high entropy alloy fabricated by laser powder bed fusion, J. Mater. Sci.
Technol. 150 (2023) 75–85, https://doi.org/10.1016/j.jmst.2022.11.045.
[272] L. Lan, W. Wang, Z. Cui, X. Hao, Effect of scanning speed on microstructure and
mechanical properties of selective laser melting AlCoCrFeNi2. 1 eutectic highentropy alloy, pp. 133321-1–4, Mater. Lett. 330 (2023), https://doi.org/10.1016/
j.matlet.2022.133321.
[273] X. Chen, J. Kong, J. Li, S. Feng, H. Li, Q. Wang, et al., High-strength
AlCoCrFeNi2.1 eutectic high entropy alloy with ultrafine lamella structure via
additive manufacturing, pp. 143816-1–12, Mater. Sci. Eng.: A 854 (2022),
https://doi.org/10.1016/j.msea.2022.143816.
[274] S. Luo, Y. Su, Z. Wang, Tailored microstructures and strengthening mechanisms in
an additively manufactured dual-phase high-entropy alloy via selective laser
melting, Sci. China Mater. 63 (7) (2020) 1279–1290, https://doi.org/10.1007/
s40843-020-1291-9.
[275] L. Huang, Y. Sun, X. Zhao, C. Wu, P. Dong, Q. Yang, et al., Preparation of
ultrahigh-strength and ductile nano-lamellar eutectic high-entropy alloy via laser
powder bed fusion, Intermetallics 165 (2024). 〈https://doi-org.remotexs.ntu.edu.
sg/10.1016/j.intermet.2023.108165〉, pp. 108165-1–10.
[276] A. Mehta, T. Huynh, N. Kljestan, K. Graydon, A. Mahmud, M. Knezevic, et al.,
Additive manufacturing of Al18Co30Cr10Fe10Ni32 high entropy alloy by gas
atomization and laser powder bed fusion, Mater. Lett. 350 (2023). 〈https://doi-or
g.remotexs.ntu.edu.sg/10.1016/j.matlet.2023.134942〉, pp. 134942-1–4.
[277] X. Chen, J. Kong, S. Feng, K. Dong, Y. Liang, Q. Wang, et al., A precipitationstrengthened high-entropy alloy prepared by selective laser melting in-situ
alloying and post-heat treatment, pp. 168145-1–13, J. Alloy. Compd. 936 (2022),
https://doi.org/10.1016/j.jallcom.2022.168145.
[278] H. Zhang, J. Cai, J. Geng, X. Sun, Y. Zhao, X. Guo, et al., Development of high
strength high plasticity refractory high entropy alloy based on Mo element
optimization and advanced forming process, pp. 106163-1–12, Int. J. Refract.
Met. Hard Mater. 112 (2023), https://doi.org/10.1016/j.ijrmhm.2023.106163.
[279] S. Lee, K.T. Kim, J.-H. Yu, H.S. Kim, J.W. Bae, J.M. Park, Cryogenic Tensile
Behavior of Ferrous Medium-entropy Alloy Additively Manufactured by Laser
Powder Bed Fusion, J. Powder Mater. 31 (1) (2024) 8–15, https://doi.org/
10.4150/KPMI.2024.31.1.8.
[280] J.M. Park, J. Choe, J.G. Kim, J.W. Bae, J. Moon, S. Yang, et al., Superior tensile
properties of 1% C-CoCrFeMnNi high-entropy alloy additively manufactured by
selective laser melting, Mater. Res. Lett. 8 (1) (2020) 1–7, https://doi.org/
10.1080/21663831.2019.1638844.
[281] R. Zhou, Y. Liu, C. Zhou, S. Li, W. Wu, M. Song, et al., Microstructures and
mechanical properties of C-containing FeCoCrNi high-entropy alloy fabricated by
selective laser melting, Intermetallics 94 (2018) 165–171, https://doi.org/
10.1016/j.intermet.2018.01.002.
[282] E.P. George, W. Curtin, C.C. Tasan, High entropy alloys: A focused review of
mechanical properties and deformation mechanisms, Acta Mater. 188 (2020)
435–474, https://doi.org/10.1016/j.actamat.2019.12.015.
[283] T. Han, J. Chen, Z. Wei, N. Qu, Y. Liu, D. Yang, et al., Effect of cooling rate on
microstructure and mechanical properties of AlCrFe2Ni2 medium entropy alloy
fabricated by laser powder bed fusion, J. Mater. Res. Technol. 25 (2023)
4063–4073, https://doi.org/10.1016/j.jmrt.2023.06.241.
[284] J. Cai, H. Zhang, L. Wang, X. Sun, X. Xu, X. Guo, et al., Design and coherent
strengthening of ultra-high strength refractory high entropy alloys based on laser
additive manufacturing, pp. 145681-1–11, Mater. Sci. Eng.: A 886 (2023),
https://doi.org/10.1016/j.msea.2023.145681.
[285] C. Zhang, K. Feng, H. Kokawa, Z. Li, K. Chen, Microstructure transition and
mechanical properties of friction stir processed CoCrFeMnNi high entropy alloy
fabricated by laser powder bed fusion, pp. 143254-1–22, Mater. Sci. Eng.: A 845
(2022), https://doi.org/10.1016/j.msea.2022.143254.
[286] Y. Hou, H. Su, H. Zhang, X. Wang, C. Wang, Fabricating Homogeneous FeCoCrNi
High-Entropy Alloys via SLM in situ alloying, pp. 942-1–17, Metals 11 (6) (2021),
https://doi.org/10.3390/met11060942.
[287] Y.O. Kuzminova, E.A. Kudryavtsev, J.-K. Han, M. Kawasaki, S.A. Evlashin, Phase
and structural changes during heat treatment of additive manufactured CrFeCoNi
high-entropy alloy, pp. 161495-1–11, J. Alloy. Compd. 889 (2021), https://doi.
org/10.1016/j.jallcom.2021.161495.
additive manufacturing and strength enhancement: Process, particle behavior and
effects, Powder Technol. 360 (2020) 509–521, https://doi.org/10.1016/j.
powtec.2019.10.068.
[245] B. Li, L. Zhang, B. Yang, Grain refinement and localized amorphization of
additively manufactured high-entropy alloy matrix composites reinforced by
nano ceramic particles via selective-laser-melting/remelting, Compos. Commun.
19 (2020) 56–60, https://doi.org/10.1016/j.coco.2020.03.001.
[246] W. Ji, M.S. Wu, Nanoscale origin of the crystalline-to-amorphous phase
transformation and damage tolerance of Cantor alloys at cryogenic temperatures,
pp. 117639-1–11, Acta Mater. (2022), https://doi.org/10.1016/j.
actamat.2022.117639.
[247] K. Ming, W. Lu, Z. Li, X. Bi, J. Wang, Amorphous bands induced by low
temperature tension in a non-equiatomic CrMnFeCoNi alloy, Acta Mater. 188
(2020) 354–365, https://doi.org/10.1016/j.actamat.2020.02.024.
[248] C.K. Ng, K. Bai, D. Wuu, K.B. Lau, J.J. Lee, A.K.H. Cheong, et al., Additive
manufacturing of high-strength and ductile high entropy alloy CoCrFeNiW0. 2
composites via laser powder bed fusion and post-annealing, J. Alloy. Compd. 906
(2022) 1–12, https://doi.org/10.1016/j.jallcom.2022.164288, 164288.
[249] C. Zhang, J. Zhu, G. Zhang, Y. Hu, Laser powder bed fusion of nano-TiB2
reinforced FeCoNiCr high-entropy alloy with enhanced strength and firm
corrosion resistance, pp. 167110-1–10, J. Alloy. Compd. 927 (2022), https://doi.
org/10.1016/j.jallcom.2022.167110.
[250] X. Wang, X. Pan, P. Sun, C. Qiu, Significant enhancement in tensile strength and
work hardening rate in CoCrFeMnNi by adding TiAl particles via selective laser
melting, pp. 142285-1–9, Mater. Sci. Eng.: A 831 (2022), https://doi.org/
10.1016/j.msea.2021.142285.
[251] Z. Ma, Q. Zhai, K. Wang, G. Chen, X. Yin, Q. Zhang, et al., Fabrication of Fe-based
metallic glass reinforced FeCoNiCrMn high-entropy alloy through additive
manufacturing: mechanical property enhancement and corrosion resistance
improvement, J. Mater. Res. Technol. 16 (2022) 899–911, https://doi.org/
10.1016/j.jmrt.2021.12.045.
[252] N. Li, S. Wu, D. Ouyang, J. Zhang, L. Liu, Fe-based metallic glass reinforced
FeCoCrNiMn high entropy alloy through selective laser melting, pp. 153695-1–8,
J. Alloy. Compd. 822 (2020), https://doi.org/10.1016/j.jallcom.2020.153695.
[253] X. Pan, C. Qiu, Influence of quasi-crystal particles and processing condition on
microstructure and tensile properties of a selective laser melted high entropy
alloy, pp. 111480-1–14, Vacuum 205 (2022), https://doi.org/10.1016/j.
vacuum.2022.111480.
[254] S. Xi, H. Chen, J. Zhou, L. Zheng, W. Wang, H. Nie, et al., A novel eutectic highentropy matrix composites were prepared by selective laser melting:
Microstructure evolution, strengthening and fracture mechanism, J. Manuf.
Process. 120 (2024) 1035–1048, https://doi.org/10.1016/j.jmapro.2024.04.085.
[255] N. Sohrabi, R. Ran, P.A. Duro, C. Cayron, J. Jhabvala, V. Pejchal, et al., Laser
powder-bed fusion of a high entropy alloy with outstanding intrinsic mechanical
properties, pp. 169209-1–11, J. Alloy. Compd. 945 (2023), https://doi.org/
10.1016/j.jallcom.2023.169209.
[256] G. Firstov, T. Kosorukova, Y.N. Koval, V. Odnosum, High entropy shape memory
alloys, Mater. Today.: Proc. 2 (2015) S499–S503, https://doi.org/10.1016/j.
matpr.2015.07.335.
[257] C. Zhang, K. Feng, H. Kokawa, Z. Li, Correlation between microstructural
heterogeneity and anisotropy of mechanical properties of laser powder bed fused
CoCrFeMnNi high entropy alloy, pp. 143920-1–16, Mater. Sci. Eng.: A 855
(2022), https://doi.org/10.1016/j.msea.2022.143920.
[258] X.-H. Gu, T. Lu, T. Zhang, W. Guo, Y. Pan, T. Dai, Anisotropy of microstructures
and mechanical properties in FeCoNiCr0. 5 high-entropy alloy prepared via
selective laser melting, Rare Met. 41 (6) (2022) 2047–2054, https://doi.org/
10.1007/s12598-021-01922-x.
[259] S. Yang, Y. Liu, H. Chen, Y. Wang, K. Kosiba, Laser powder bed fusion of Fe60
(CoCrNiMn) 40 medium-entropy alloy with excellent strength-ductility balance,
pp. 112720-1–13, Mater. Des. 238 (2024), https://doi.org/10.1016/j.
matdes.2024.112720.
[260] B. Dovgyy, A. Piglione, P.A. Hooper, M.-S. Pham, Comprehensive assessment of
the printability of CoNiCrFeMn in laser powder bed fusion, pp. 108845-1–16,
Mater. Des. 194 (2020), https://doi.org/10.1016/j.matdes.2020.108845.
[261] G. Karthik, Y. Kim, E.S. Kim, A. Zargaran, P. Sathiyamoorthi, J.M. Park, et al.,
Gradient heterostructured laser-powder bed fusion processed CoCrFeMnNi high
entropy alloy, pp. 103131-1–18, Addit. Manuf. 59 (2022), https://doi.org/
10.1016/j.addma.2022.103131.
[262] Y.-K. Kim, M.-C. Kim, K.-A. Lee, 1.45 GPa ultrastrong cryogenic strength with
superior impact toughness in the in-situ nano oxide reinforced CrMnFeCoNi highentropy alloy matrix nanocomposite manufactured by laser powder bed fusion,
J. Mater. Sci. Technol. 97 (2022) 10–19, https://doi.org/10.1016/j.
jmst.2021.04.030.
[263] Z. Fu, B. Yang, K. Gan, D. Yan, Z. Li, G. Gou, et al., Improving the hydrogen
embrittlement resistance of a selective laser melted high-entropy alloy via
modifying the cellular structures, pp. 109695-1–12, Corros. Sci. 190 (2021),
https://doi.org/10.1016/j.corsci.2021.109695.
[264] Y. Brif, M. Thomas, I. Todd, The use of high-entropy alloys in additive
manufacturing, Scr. Mater. 99 (2015) 93–96, https://doi.org/10.1016/j.
scriptamat.2014.11.037.
[265] D. Lin, L. Xu, H. Jing, Y. Han, L. Zhao, F. Minami, Effects of annealing on the
structure and mechanical properties of FeCoCrNi high-entropy alloy fabricated
via selective laser melting, pp. 101058-1–11, Addit. Manuf. 32 (2020), https://
doi.org/10.1016/j.addma.2020.101058.
[266] H. Cheng, H. Luo, Z. Pan, X. Wang, Q. Zhao, Y. Fu, et al., Effects of laser powder
bed fusion process parameters on microstructure and hydrogen embrittlement of
43
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
[288] Y. Kuzminova, A. Shibalova, S. Evlashin, I. Shishkovsky, P. Krakhmalev,
Structural effect of low Al content in the in-situ additive manufactured
CrFeCoNiAlx high-entropy alloy, pp. 130487-1–5, Mater. Lett. 303 (2021),
https://doi.org/10.1016/j.matlet.2021.130487.
[289] T. Yonezawa, K. Suzuki, S. Ooki, A. Hashimoto, The effect of chemical
composition and heat treatment conditions on stacking fault energy for Fe-Cr-Ni
austenitic stainless steel, Metall. Mater. Trans. A 44 (13) (2013) 5884–5896,
https://doi.org/10.1007/s11661-013-1943-0.
[290] F. Wang, T. Yuan, R. Li, S. Lin, P. Niu, V. Cristino, Effect of Mo on the
morphology, microstructure and mechanical properties of NbTa0. 5TiMox
refractory high entropy alloy fabricated by laser powder bed fusion using
elemental mixed powders, pp. 106107-1–14, Int. J. Refract. Met. Hard Mater. 111
(2023), https://doi.org/10.1016/j.ijrmhm.2023.106107.
[291] L. Lan, Z. Yang, W. Wang, Z. Cui, X. Hao, Effect of initial powder particle size on
densification behavior and mechanical properties of laser additive manufacturing
of AlCoCrFeNi2. 1 eutectic high-entropy alloy, pp. 118379-1–10, Powder
Technol. 420 (2023), https://doi.org/10.1016/j.powtec.2023.118379.
[292] T. Yu, G. Zhou, Y. Cheng, F. Hu, T. Jiang, T. Sun, et al., Microstructure and
properties of AlCoCrFeNi2. 1 eutectic high entropy alloy manufactured by
selective laser melting, pp. 109396-1–14, Opt. Laser Technol. 163 (2023),
https://doi.org/10.1016/j.optlastec.2023.109396.
[293] A.A. Akinwande, O.A. Balogun, A.A. Adediran, O.S. Adesina, V. Romanovski, T.
C. Jen, Experimental analysis, statistical modeling, and parametric optimization
of quinary-(CoCrFeMnNi) 100–x/TiCx high-entropy-alloy (HEA) manufactured by
laser additive manufacturing, pp. 100802-1–18, Results Eng. 17 (2023), https://
doi.org/10.1016/j.rineng.2022.100802.
[294] J. Karimi, L. Kollo, R. Rahmani, P. Ma, Y. Jia, K. Prashanth, Selective laser
melting of in-situ CoCrFeMnNi high entropy alloy: Effect of remelting, J. Manuf.
Process. 84 (2022) 55–63, https://doi.org/10.1016/j.jmapro.2022.09.056.
[295] W. Zhao, Significance of grain refinement on micro-mechanical properties and
structures of additively-manufactured CoCrFeNi high-entropy alloy, pp. 1408981–10, Mater. Sci. Eng.: A 807 (2021), https://doi.org/10.1016/j.
msea.2021.140898.
[296] F. Peyrouzet, D. Hachet, R. Soulas, C. Navone, S. Godet, S. Gorsse, Selective laser
melting of Al 0.3 CoCrFeNi high-entropy alloy: Printability, microstructure, and
mechanical properties, Jom 71 (10) (2019) 3443–3451, https://doi.org/10.1007/
s11837-019-03715-1.
[297] Z. Li, K.G. Pradeep, Y. Deng, D. Raabe, C.C. Tasan, Metastable high-entropy dualphase alloys overcome the strength-ductility trade-off, pp. 227-30-1–8, Nature
534 (7606) (2016), https://doi.org/10.1038/nature17981.
[298] F. Qihong, C. Y, L. Jia, L. Bin, L. Yong, K.L. Peter, Probing the phase
transformation and dislocation evolution in dual-phase HEA, Int. J. Plast. 114
(2019) 161–173, https://doi.org/10.1016/j.ijplas.2018.10.014.
[299] F. Otto, A. Dlouhý, C. Somsen, H. Bei, G. Eggeler, E.P. George, The influences of
temperature and microstructure on the tensile properties of a CoCrFeMnNi highentropy alloy, Acta Mater. 61 (15) (2013) 5743–5755, https://doi.org/10.1016/j.
actamat.2013.06.018.
[300] Y. Zhu, X. Wu, Heterostructured materials, pp. 101019-1–55, Prog. Mater. Sci.
131 (2023), https://doi.org/10.1016/j.pmatsci.2022.101019.
[301] Z. Lei, X. Liu, Y. Wu, H. Wang, S. Jiang, S. Wang, et al., Enhanced strength and
ductility in a high-entropy alloy via ordered oxygen complexes, Nature 563
(7732) (2018) 546–550, https://doi.org/10.1038/s41586-018-0685-y.
[302] W. Ji, R. Zhou, P. Vivegananthan, M.S. Wu, H. Gao, K. Zhou, Recent progress in
gradient-structured metals and alloys, pp. 101194-1–55, Prog. Mater. Sci. (2023),
https://doi.org/10.1016/j.pmatsci.2023.101194.
[303] F. Haftlang, J.B. Seol, A. Zargaran, J. Moon, H.S. Kim, Chemical core-shell
metastability-induced large ductility in medium-entropy maraging and reversion
alloys, pp. 119115-1–13, Acta Mater. 256 (2023), https://doi.org/10.1016/j.
actamat.2023.119115.
[304] H. Chung, W.S. Choi, H. Jun, H.-S. Do, B.-J. Lee, P.-P. Choi, et al., Doubled
strength and ductility via maraging effect and dynamic precipitate transformation
in ultrastrong medium-entropy alloy, pp. 145-1–10, Nat. Commun. 14 (1) (2023),
https://doi.org/10.1038/s41467-023-35863-z.
[305] L. Fan, T. Yang, Y. Zhao, J. Luan, G. Zhou, H. Wang, et al., Ultrahigh strength and
ductility in newly developed materials with coherent nanolamellar architectures,
pp. 6240-1–8, Nat. Commun. 11 (1) (2020), https://doi.org/10.1038/s41467020-20109-z.
[306] C. Zhang, H. Wang, X. Wang, Y.T. Tang, Q. Yu, C. Zhu, et al., Strong and ductile
refractory high-entropy alloys with super formability, pp. 118602-1–11, Acta
Mater. 245 (2023), https://doi.org/10.1016/j.actamat.2022.118602.
[307] J. Schijve, Fatigue of structures and materials in the 20th century and the state of
the art, Int. J. Fatigue 25 (8) (2003) 679–702, https://doi.org/10.1016/S01421123(03)00051-3.
[308] Z. Qu, Z. Zhang, R. Liu, L. Xu, Y. Zhang, X. Li, et al., High fatigue resistance in a
titanium alloy via near-void-free 3D printing, Nature 626 (8001) (2024)
999–1004, https://doi.org/10.1038/s41586-024-07048-1.
[309] Y.K. Kim, K.R. Lim, K.A. Lee, Superior resistance to high–temperature creep in an
additively manufactured precipitation–hardened CrMnFeCoNi high–entropy alloy
nanocomposite, pp. 111761-1–5, Mater. Des. 227 (2023), https://doi.org/
10.1016/j.matdes.2023.111761.
[310] Y.B. Kang, S.H. Shim, K.H. Lee, S.I. Hong, Dislocation creep behavior of
CoCrFeMnNi high entropy alloy at intermediate temperatures, Mater. Res. Lett. 6
(12) (2018) 689–695, https://doi.org/10.1080/21663831.2018.1543731.
[311] B. Gludovatz, A. Hohenwarter, D. Catoor, E.H. Chang, E.P. George, R.O. Ritchie,
A fracture-resistant high-entropy alloy for cryogenic applications, Science 345
(6201) (2014) 1153–1158, https://doi.org/10.1126/science.1254581.
[312] P. Kumar, M. Michalek, D.H. Cook, H. Sheng, K.B. Lau, P. Wang, et al., On the
strength and fracture toughness of an additive manufactured CrCoNi mediumentropy alloy, pp. 119249-1–12, Acta Mater. 258 (2023), https://doi.org/
10.1016/j.actamat.2023.119249.
[313] Y. Ren, L. Liang, Q. Shan, A. Cai, J. Du, Q. Huang, et al., Effect of volumetric
energy density on microstructure and tribological properties of FeCoNiCuAl highentropy alloy produced by laser powder bed fusion, Virtual Phys. Prototyp. 15
(2020) 543–554, https://doi.org/10.1080/17452759.2020.1848284.
[314] D. Kumar, Recent Advances in Tribology of High Entropy Alloys: A Critical
Review, pp. 101106-1–122, Prog. Mater. Sci. 136 (2023), https://doi.org/
10.1016/j.pmatsci.2023.101106.
[315] C. Shuai, J. Xie, X. Jiang, S. Peng, C. Wang, Additively manufactured high entropy
alloy with high wear resistance for biomedical implant, pp. 112939-1–7, Vacuum
221 (2024), https://doi.org/10.1016/j.vacuum.2023.112939.
[316] C. Bulut, F. Yıldız, T. Varol, T.O. Ergüder, Effect of titanium on the structural,
mechanical and surface properties of CoCrFeMnNiTix high entropy alloy
fabricated by selective laser melting, pp. 108281-1–15, Intermetallics 169 (2024),
https://doi.org/10.1016/j.intermet.2024.108281.
[317] S. Xi, H. Chen, J. Zhou, L. Zheng, W. Wang, Q. Zheng, Microstructure evolution
and wear resistance of a novel ceramic particle-reinforced high-entropy alloy
prepared by laser powder bed fusion, Ceram. Int. 50 (4) (2024) 5962–5973,
https://doi.org/10.1016/j.ceramint.2023.11.162.
[318] G. Koch, Cost of corrosion, Trends oil Gas, Corros. Res. Technol. (2017) 3–30,
https://doi.org/10.1016/B978-0-08-101105-8.00001-2.
[319] S. Sarkar, P.K. Sarswat, M.L. Free, Elevated temperature corrosion resistance of
additive manufactured single phase AlCoFeNiTiV0. 9Sm0. 1 and AlCoFeNiV0.
9Sm0. 1 HEAs in a simulated syngas atmosphere, pp. 100902-1–10, Addit. Manuf.
30 (2019), https://doi.org/10.1016/j.addma.2019.100902.
[320] H. Cheng, Z. Liu, H. Luo, Z. Pan, X. Wang, Q. Zhao, et al., Tuning the
microstructure to improve corrosion resistance of additive manufacturing highentropy alloy in proton exchange membrane fuel cells environment, pp. 1109691–16, Corros. Sci. 213 (2023), https://doi.org/10.1016/j.corsci.2023.110969.
[321] Y.Z. Lek, C. Wang, X. Shen, Z. Chen, U. Ramamurty, K. Zhou, Additive
manufacturing of corrosion-resistant maraging steel M789 by directed energy
deposition, pp. 144032-1–12, Mater. Sci. Eng.: A 857 (2022), https://doi.org/
10.1016/j.msea.2022.144032.
[322] B. Li, C. Han, C.W.J. Lim, K. Zhou, Interface formation and deformation behaviors
of an additively manufactured nickel-aluminum-bronze/15-5 PH multimaterial
via laser-powder directed energy deposition, pp. 142101-1–15, Mater. Sci. Eng.: A
829 (2022), https://doi.org/10.1016/j.msea.2021.142101.
[323] Y. Chen, T. Duval, U. Hung, J. Yeh, H. Shih, Microstructure and electrochemical
properties of high entropy alloys—a comparison with type-304 stainless steel,
Corros. Sci. 47 (9) (2005) 2257–2279, https://doi.org/10.1016/j.
corsci.2004.11.008.
[324] V. Vukkum, R. Gupta, Review on corrosion performance of laser powder-bed
fusion printed 316L stainless steel: Effect of processing parameters,
manufacturing defects, post-processing, feedstock, and microstructure, pp.
110874-1–45, Mater. Des. 221 (2022), https://doi.org/10.1016/j.
matdes.2022.110874.
[325] Y. Fu, J. Li, H. Luo, C. Du, X. Li, Recent advances on environmental corrosion
behavior and mechanism of high-entropy alloys, J. Mater. Sci. Technol. 80 (2021)
217–233, https://doi.org/10.1016/j.jmst.2020.11.044.
[326] R. Shu, E.-M. Paschalidou, S.G. Rao, B. Bakhit, R. Boyd, M.V. Moro, et al., Effect of
nitrogen content on microstructure and corrosion resistance of sputter-deposited
multicomponent (TiNbZrTa) Nx films, pp. 126485-1–10, Surf. Coat. Technol. 404
(2020), https://doi.org/10.1016/j.surfcoat.2020.126485.
[327] E.-M. Paschalidou, R. Shu, R. Boyd, A.A. Papaderakis, B. Bakhit, A. Le Febvrier, et
al., The effect of the Nb concentration on the corrosion resistance of nitrogencontaining multicomponent TiZrTaNb-based films in acidic environments, pp.
167005-1–12. J. Alloy. Compd. 927 (2022) https://doi.org/10.1016/j.
jallcom.2022.167005.
[328] Z. Xu, H. Zhang, X. Du, Y. He, H. Luo, G. Song, et al., Corrosion resistance
enhancement of CoCrFeMnNi high-entropy alloy fabricated by additive
manufacturing, pp. 108954-1–11, Corros. Sci. 177 (2020), https://doi.org/
10.1016/j.corsci.2020.108954.
[329] G. Wang, Q. Liu, H. Rao, H. Liu, C. Qiu, Influence of porosity and microstructure
on mechanical and corrosion properties of a selectively laser melted stainless
steel, pp. 154815-1–9, J. Alloy. Compd. 831 (2020), https://doi.org/10.1016/j.
jallcom.2020.154815.
[330] H. Zhang, Y. Zhao, S. Huang, S. Zhu, F. Wang, D. Li, Manufacturing and analysis
of high-performance refractory high-entropy alloy via selective laser melting
(SLM), pp. 720-1–11, Materials 12 (5) (2019), https://doi.org/10.3390/
ma12050720.
[331] Z. Zhang, X. Li, H. Yi, H. Xie, Z. Zhao, P. Bai, Clarify the role of Nb alloying on
passive film and corrosion behavior of CoCrFeMnNi high entropy alloy fabricated
by laser powder bed fusion, pp. 111510-1–15, Corros. Sci. 224 (2023), https://
doi.org/10.1016/j.corsci.2023.111510.
[332] H. Peng, Z. Lin, R. Li, P. Niu, Z. Zhang, Corrosion behavior of an equiatomic
CoCrFeMnNi high-entropy alloy-a comparison between selective laser melting
and cast, pp. 244-1–11, Front. Mater. 7 (2020), https://doi.org/10.3389/
fmats.2020.00244.
[333] J. Ren, C. Mahajan, L. Liu, D. Follette, W. Chen, S. Mukherjee, Corrosion behavior
of selectively laser melted CoCrFeMnNi high entropy alloy, pp. 1029-1–12, Metals
9 (10) (2019), https://doi.org/10.3390/met9101029.
[334] R. Li, D. Kong, K. He, Y. Zhou, C. Dong, Improved passivation ability via tuning
dislocation cell substructures for FeCoCrNiMn high-entropy alloy fabricated by
44
A. Jarlöv et al.
Materials Science & Engineering R 161 (2024) 100834
1–37, J. Magn. Magn. Mater. 554 (2022), https://doi.org/10.1016/j.
jmmm.2022.169142.
[358] ReportLinker, Soft Magnetic Materials Market by Material and End Use: Global
Opportunity Analysis and Industry Forecast, 2019–2026“ 2019.
[359] P. Yvon, F. Carré, Structural materials challenges for advanced reactor systems,
J. Nucl. Mater. 385 (2) (2009) 217–222, https://doi.org/10.1016/j.
jnucmat.2008.11.026.
[360] M. Moschetti, A. Xu, B. Schuh, A. Hohenwarter, J.-P. Couzinie, J.J. Kruzic, et al.,
On the room-temperature mechanical properties of an ion-irradiated TiZrNbHfTa
refractory high entropy alloy, Jom 72 (2020) 130–138, https://doi.org/10.1007/
s11837-019-03861-6.
[361] T. Shi, P.-H. Lei, X. Yan, J. Li, Y.-D. Zhou, Y.-P. Wang, et al., Current development
of body-centered cubic high-entropy alloys for nuclear applications, Tungsten 3
(2) (2021) 197–217, https://doi.org/10.1007/s42864-021-00115-4.
[362] H. Li, Y. Mu, G. Wang, Y. Jia, R. Wang, Effect of annealing on irradiation
resistance of (FeCoNi)86Al7Ti7 high entropy alloys, pp. 131970-1–4, Mater. Lett.
316 (2022), https://doi.org/10.1016/j.matlet.2022.131970.
[363] O. El Atwani, H. Vo, M. Tunes, C. Lee, A. Alvarado, N. Krienke, et al., A quinary
WTaCrVHf nanocrystalline refractory high-entropy alloy withholding extreme
irradiation environments, pp. 2516-1–12, Nat. Commun. 14 (1) (2023), https://
doi.org/10.1038/s41467-023-38000-y.
[364] M. Dada, P. Popoola, N. Mathe, Recent advances of high entropy alloys for
aerospace applications: A review, World J. Eng. 20 (1) (2023) 43–74, https://doi.
org/10.1108/WJE-01-2021-0040.
[365] K. Tseng, A light-weight high-entropy alloy Al20Be20Fe10Si15Ti35, Sci. China
Technol. Sci. 61 (2) (2018) 184–188, https://doi.org/10.1007/s11431-017-90730.
[366] S. O’Brien, J. Christudasjustus, L. Esteves, S. Vijayan, J. Jinschek, N. Birbilis, et
al., A low-cost, low-density, and corrosion resistant AlFeMnSi compositionally
complex alloy, npj Mater. Degrad. 5 (1) (2021) 1–10, https://doi.org/10.1038/
s41529-021-00158-5.
[367] Y. Qiu, S. Thomas, M. Gibson, H. Fraser, K. Pohl, N. Birbilis, Microstructure and
corrosion properties of the low-density single-phase compositionally complex
alloy AlTiVCr, Corros. Sci. 133 (2018) 386–396, https://doi.org/10.1016/j.
corsci.2018.01.035.
[368] S.N. Harithsa, S.A. Kumar, R. Velu, B. Nagesha, Laser powder bed fusion
technique of hydrogen–fueled gas turbine: Role of advanced materials and its
challenges, Mater. Today.: Proc. 90 (2023) 11–14, https://doi.org/10.1016/j.
matpr.2023.03.389.
[369] X. Ma, P. Ruggiero, R. Bhattacharya, O.N. Senkov, A. Rai, Evaluation of new high
entropy alloy as thermal sprayed bondcoat in thermal barrier coatings, J. Therm.
Spray. Technol. (2021) 1–10, https://doi.org/10.1007/s11666-021-01279-8.
[370] K. Ren, Q. Wang, G. Shao, X. Zhao, Y. Wang, Multicomponent high-entropy
zirconates with comprehensive properties for advanced thermal barrier coating,
Scr. Mater. 178 (2020) 382–386, https://doi.org/10.1016/j.
scriptamat.2019.12.006.
[371] S. Yuan, C.K. Chua, K. Zhou, 3D-printed mechanical metamaterials with high
energy absorption, pp. 1800419-1–9, Adv. Mater. Technol. 4 (3) (2019), https://
doi.org/10.1002/admt.201800419.
[372] Y. Tian, K. Chen, H. Zheng, D.R. Kripalani, Z. Zeng, A. Jarlöv, et al., Additively
Manufactured Dual-Faced Structured Fabric for Shape-Adaptive Protection, Adv.
Sci. (2023) 1–11, https://doi.org/10.1002/advs.202301567, 2301567.
[373] L. Pollock, A.K. Abdelwahab, J. Murray, G. Wild, The Need for Aerospace
Structural Health Monitoring: A review of aircraft fatigue accidents, Progn.
Health Manag. Soc. 12 (3) (2021) 1–16, https://doi.org/10.36001/IJPHM.2021.
v12i3.2368.
[374] M. Wehmöller, P.H. Warnke, C. Zilian, H. Eufinger, Implant design and
production—a new approach by selective laser melting, Int. Congr. Ser. 1281
(2005) 690–695, https://doi.org/10.1016/j.ics.2005.03.155.
[375] E. Liverani, A. Fortunato, A. Leardini, C. Belvedere, S. Siegler, L. Ceschini, et al.,
Fabrication of Co–Cr–Mo endoprosthetic ankle devices by means of Selective
Laser Melting (SLM), Mater. Des. 106 (2016) 60–68, https://doi.org/10.1016/j.
matdes.2016.05.083.
[376] A.L. Jardini, M.A. Larosa, R. Maciel Filho, C.A. de Carvalho Zavaglia, L.
F. Bernardes, C.S. Lambert, et al., Cranial reconstruction: 3D biomodel and
custom-built implant created using additive manufacturing, J. Cranio-Maxillofac.
Surg. 42 (8) (2014) 1877–1884, https://doi.org/10.1016/j.jcms.2014.07.006.
[377] Q.-T. Song, J. Xu, TiZrNbTa) 90Mo10 high-entropy alloy: Electrochemical
behavior and passive film characterization under exposure to Ringer’s solution,
pp. 108513-1–16, Corros. Sci. 167 (2020), https://doi.org/10.1016/j.
corsci.2020.108513.
[378] S.-P. Wang, J. Xu, TiZrNbTa)-Mo high-entropy alloys: dependence of
microstructure and mechanical properties on Mo concentration and modeling of
solid solution strengthening, Intermetallics 95 (2018) 59–72, https://doi.org/
10.1016/j.intermet.2018.01.017.
[379] R. Ozasa, A. Matsugaki, T. Ishimoto, T. Nakano, Research and Development of
Titanium-Containing Biomedical High Entropy Alloys (BioHEAs) Utilizing Rapid
Solidification via Laser-Powder Bed Fusion, Mater. Trans. 64 (1) (2023) 31–36,
https://doi.org/10.2320/matertrans.MT-MLA2022011.
[380] D. Zhao, H. Liang, C. Han, J. Li, J. Liu, K. Zhou, et al., 3D printing of a titaniumtantalum Gyroid scaffold with superb elastic admissible strain, bioactivity and insitu bone regeneration capability, pp. 102223-1–16, Addit. Manuf. 47 (2021),
https://doi.org/10.1016/j.addma.2021.102223.
[381] Z. Dong, C. Han, Y. Zhao, J. Huang, C. Ling, G. Hu, et al., Role of heterogenous
microstructure and deformation behavior in achieving superior strength-ductility
laser powder bed fusion, pp. 156856-1–13, Appl. Surf. Sci. 621 (2023), https://
doi.org/10.1016/j.apsusc.2023.156856.
[335] K. Sieradzki, R. Newman, A percolation model for passivation in stainless steels,
J. Electrochem. Soc. 133 (9) (1986) 1979–1980. https://citeseerx.ist.psu.edu/doc
ument?repid=rep1&type=pdf&doi=45fcdb086da165d0b7077c6aface3a2bc
55853f5.
[336] L.Z. Medina, L. Mølmen, E.M. Paschalidou, O. Donzel-Gargand, P. Leisner,
U. Jansson, et al., Extending the Passive Region of CrFeNi-Based High Entropy
Alloys, pp. 2307897-1–19, Adv. Funct. Mater. 33 (51) (2023), https://doi.org/
10.1002/adfm.202307897.
[337] C. Xu, W. Gao, Pilling-Bedworth ratio for oxidation of alloys, Mater. Res. Innov. 3
(2000) 231–235, https://doi.org/10.1007/s100190050008.
[338] C. Zeng, A. Neils, J. Lesko, N. Post, Machine learning accelerated discovery of
corrosion-resistant high-entropy alloys, pp. 112925-1–9, Comput. Mater. Sci. 237
(2024), https://doi.org/10.1016/j.commatsci.2024.112925.
[339] S.K. Dwivedi, M. Vishwakarma, Hydrogen embrittlement in different materials: A
review, Int. J. Hydrog. Energy 43 (46) (2018) 21603–21616, https://doi.org/
10.1016/j.ijhydene.2018.09.201.
[340] D.-H. Lee, J.Y. Jung, K.H. Lee, S.Y. Lee, Y. Zhao, K.B. Lau, et al., Distinct effects of
in-situ and ex-situ hydrogen charging methods on the mechanical behavior of
CoCrFeNi high-entropy alloy fabricated by laser-powder bed fusion, pp. 1688581–12, J. Alloy. Compd. 940 (2023), https://doi.org/10.1016/j.
jallcom.2023.168858.
[341] Y.-K. Kim, J.-Y. Suh, K.-A. Lee, Effect of gaseous hydrogen embrittlement on the
mechanical properties of additively manufactured CrMnFeCoNi high-entropy
alloy strengthened by in-situ formed oxide, pp. 140039-1–5, Mater. Sci. Eng.: A
796 (2020), https://doi.org/10.1016/j.msea.2020.140039.
[342] Y.-T. Lin, X. An, Z. Zhu, M.L.S. Nai, C.-W. Tsai, H.-W. Yen, Effect of cell wall on
hydrogen response in CoCrFeMnNi high-entropy alloy additively manufactured
by selective laser melting, pp. 166735-1–13, J. Alloy. Compd. 925 (2022),
https://doi.org/10.1016/j.jallcom.2022.166735.
[343] Y. Zhao, D.-H. Lee, M.-Y. Seok, J.-A. Lee, M. Phaniraj, J.-Y. Suh, et al., Resistance
of CoCrFeMnNi high-entropy alloy to gaseous hydrogen embrittlement, Scr.
Mater. 135 (2017) 54–58, https://doi.org/10.1016/j.scriptamat.2017.03.029.
[344] X. Li, J. Yin, J. Zhang, Y. Wang, X. Song, Y. Zhang, et al., Hydrogen embrittlement
and failure mechanisms of multi-principal element alloys: A review, J. Mater. Sci.
Technol. 122 (2022) 20–32, https://doi.org/10.1016/j.jmst.2022.01.008.
[345] Y.O. Kuzminova, D.G. Firsov, A.A. Shibalova, S.A. Evlashin, I.V. Shishkovsky, S.
S. Dautov, The oxidation behavior of the CrFeCoNiAlx (x= 0, 1.0, and 5.0 wt%)
high-entropy alloy synthesized with Al elemental powder via powder bed fusion
technique at high temperatures, pp. 103399-1–5, Micron 166 (2023), https://doi.
org/10.1016/j.micron.2022.103399.
[346] X. Jia, Z. Xu, Y. He, S. Zhou, X. Du, H. Zhang, et al., Oxidation Behavior of
CoCrFeMnNi High-Entropy Alloy Fabricated by Selective Laser Melting, Met.
Mater. Int. 179 (2023) 1–14, https://doi.org/10.1007/s12540-023-01415-9.
[347] T. Borkar, V. Chaudhary, B. Gwalani, D. Choudhuri, C.V. Mikler, V. Soni, et al.,
A combinatorial approach for assessing the magnetic properties of high entropy
alloys: role of Cr in AlCoxCr1–xFeNi, Adv. Eng. Mater. 19 (8) (2017) 1–13,
https://doi.org/10.1002/adem.201700048, 1700048.
[348] X. Yang, O. Heczko, J. Lehtonen, R. Björkstrand, M. Salmi, V. Uhlenwinkel, et al.,
Microstructure and Properties of Additively Manufactured AlCoCr0. 75Cu0.
5FeNi Multicomponent Alloy: Controlling Magnetic Properties by Laser Powder
Bed Fusion via Spinodal Decomposition, pp. 1801-1–24, Materials 15 (5) (2022),
https://doi.org/10.3390/ma15051801.
[349] V. Chaudhary, R. Chaudhary, R. Banerjee, R. Ramanujan, Accelerated and
conventional development of magnetic high entropy alloys, Mater. Today 49
(2021) 231–252, https://doi.org/10.1016/j.mattod.2021.03.018.
[350] S. Wei, Y. Zhao, S.-H. Li, S. Chen, K.B. Lau, V. Soh, et al., Laser powder bed fusion
of a Cu-Ni-Al alloy using the compositional grading approach, pp. 115441-1–7,
Scr. Mater. 231 (2023), https://doi.org/10.1016/j.scriptamat.2023.115441.
[351] X. Peng, X. Cao, Y. Wang, Y. Dong, Z. Li, H. Xu, et al., Design, microstructure, and
mechanical property of negative Poisson’s ratio porous structure fabricated by
LPBF of AlCoCrFeNi2. 1 eutectic high-entropy-alloy, J. Mater. Res. Technol. 24
(2023) 2028–2040, https://doi.org/10.1016/j.jmrt.2023.03.104.
[352] Y. Leng, P. Ming, D. Yang, C. Zhang, Stainless steel bipolar plates for proton
exchange membrane fuel cells: Materials, flow channel design and forming
processes, pp. 227783-1–23, J. Power Sources 451 (2020), https://doi.org/
10.1016/j.jpowsour.2020.227783.
[353] P. Huang, Z. Chen, J. Zhang, M. Wu, Y. Liu, F. Zhang, et al., Stainless steel bipolar
plate fuel cell with different flow field structures prepared by laser additive
manufacturing, pp. 122186-1–13, Int. J. Heat. Mass Transf. 183 (2022), https://
doi.org/10.1016/j.ijheatmasstransfer.2021.122186.
[354] J. Svendby, Ø. Bjelland, D. Bokach, B.G. Solheim, The use of Additive
Manufactured Inconel 625 as Bipolar Plate for the High Temperature Proton
Electrolyte Membrane Fuel Cell, Procedia Struct. Integr. 34 (2021) 51–58,
https://doi.org/10.1016/j.prostr.2021.12.008.
[355] G. Scotti, P. Kanninen, V.-P. Matilainen, A. Salminen, T. Kallio, Stainless steel
micro fuel cells with enclosed channels by laser additive manufacturing, Energy
106 (2016) 475–481, https://doi.org/10.1016/j.energy.2016.03.086.
[356] L.Z. Medina, M.V.T. da Costa, E.M. Paschalidou, G. Lindwall, L. Riekehr,
M. Korvela, et al., Enhancing corrosion resistance, hardness, and crack resistance
in magnetron sputtered high entropy CoCrFeMnNi coatings by adding carbon, pp.
109711-1–13, Mater. Des. 205 (2021), https://doi.org/10.1016/j.
matdes.2021.109711.
[357] P. Kumari, A.K. Gupta, R.K. Mishra, M. Ahmad, R.R. Shahi, A comprehensive
review: Recent progress on magnetic high entropy alloys and oxides, pp. 169142-
45
Materials Science & Engineering R 161 (2024) 100834
A. Jarlöv et al.
synergy in zinc fabricated via laser powder bed fusion, pp. 045003-1–21, Int. J.
Extrem. Manuf. 6 (2024), https://doi.org/10.1088/2631-7990/ad3929.
[382] M. Li, F. Benn, T. Derra, N. Kröger, M. Zinser, R. Smeets, et al., Microstructure,
mechanical properties, corrosion resistance and cytocompatibility of WE43 Mg
alloy scaffolds fabricated by laser powder bed fusion for biomedical applications,
pp. 111623-1–17, Mater. Sci. Eng.: C. 119 (2021), https://doi.org/10.1016/j.
msec.2020.111623.
[383] M. Chen, M. Gao, L. Bai, H. Zheng, H.J. Qi, K. Zhou, Recent Advances in 4D
Printing of Liquid Crystal Elastomers, pp. 2209566-1–31, Adv. Mater. 35 (2022),
https://doi.org/10.1002/adma.202209566.
[384] L. Xue, K. Atli, C. Zhang, N. Hite, A. Srivastava, A. Leff, et al., Laser powder bed
fusion of defect-free NiTi shape memory alloy parts with superior tensile
superelasticity, pp. 117781-1–21, Acta Mater. 229 (2022), https://doi.org/
10.1016/j.actamat.2022.117781.
[385] C. Zhang, L. Xue, K.C. Atli, R. Arróyave, I. Karaman, A. Elwany, On the
Fabrication of Defect-Free Nickel-Rich Nickel–Titanium Parts Using Laser Powder
Bed Fusion, pp. 091011-1–14, J. Manuf. Sci. Eng. 144 (9) (2022), https://doi.org/
10.1115/1.4054935.
[386] C.-H. Chen, Y.-J. Chen, Shape memory characteristics of (TiZrHf)
50Ni25Co10Cu15 high entropy shape memory alloy, Scr. Mater. 162 (2019)
185–189, https://doi.org/10.1016/j.scriptamat.2018.11.023.
[387] S.-H. Chang, W.-P. Kao, K.-Y. Hsiao, J.-W. Yeh, M.-Y. Lu, C.-W. Tsai, Hightemperature shape memory properties of Cu15Ni35Ti25Hf12. 5Zr12. 5 highentropy alloy, J. Mater. Res. Technol. 14 (2021) 1235–1242, https://doi.org/
10.1016/j.jmrt.2021.07.008.
[388] J.I. Lee, K. Tsuchiya, W. Tasaki, H.S. Oh, T. Sawaguchi, H. Murakami, et al.,
A strategy of designing high-entropy alloys with high-temperature shape memory
effect, pp. 13140-1–10, Sci. Rep. 9 (1) (2019), https://doi.org/10.1038/s41598019-49529-8.
[389] Y. Nie, H. Peng, L. Yong, D. Wang, C. Zhang, S. Wang, et al., Improvement of
shape memory effect via strengthening austenite by virtue of thermally activated
process in FCC-type metastable multicomponent alloys, pp. 139748-1–11, Mater.
Sci. Eng.: A 793 (2020), https://doi.org/10.1016/j.msea.2020.139748.
[390] R.R. Shahi, A.K. Gupta, P. Kumari, Perspectives of high entropy alloys as
hydrogen storage materials, Int. J. Hydrog. Energy 48 (56) (2022) 1–17, https://
doi.org/10.1016/j.ijhydene.2022.02.113.
[391] F. Yang, J. Wang, Y. Zhang, Z. Wu, Z. Zhang, F. Zhao, et al., Recent progress on
the development of high entropy alloys (HEAs) for solid hydrogen storage: a
review, Int. J. Hydrog. Energy 47 (21) (2022) 11236–11249, https://doi.org/
10.1016/j.ijhydene.2022.01.141.
[392] F. Marques, M. Balcerzak, F. Winkelmann, G. Zepon, M. Felderhoff, Review and
outlook on high-entropy alloys for hydrogen storage, Energy Environ. Sci. 14 (10)
(2021) 5191–5227, https://doi.org/10.1039/d1ee01543e.
[393] J. Liu, J. Xu, S. Sleiman, F. Ravalison, W. Zhu, H. Liu, et al., Hydrogen storage
properties of V0. 3Ti0. 3Cr0. 25Mn0. 1Nb0. 05 high entropy alloy, Int. J. Hydrog.
Energy 47 (61) (2022) 25724–25732, https://doi.org/10.1016/j.
ijhydene.2022.06.013.
[394] S. Yang, F. Yang, C. Wu, Y. Chen, Y. Mao, L. Luo, Hydrogen storage and cyclic
properties of (VFe) 60 (TiCrCo) 40-xZrx (0≤ x≤ 2) alloys, J. Alloy. Compd. 663
(2016) 460–465, https://doi.org/10.1016/j.jallcom.2015.12.125.
[395] B.H. Silva, C. Zlotea, Y. Champion, W.J. Botta, G. Zepon, Design of TiVNb-(Cr, Ni
or Co) multicomponent alloys with the same valence electron concentration for
hydrogen storage, pp. 158767-1–12, J. Alloy. Compd. 865 (2021), https://doi.
org/10.1016/j.jallcom.2021.158767.
[396] I. Kunce, M. Polanski, J. Bystrzycki, Microstructure and hydrogen storage
properties of a TiZrNbMoV high entropy alloy synthesized using Laser Engineered
Net Shaping (LENS), Int. J. Hydrog. Energy 39 (18) (2014) 9904–9910, https://
doi.org/10.1016/j.ijhydene.2014.02.067.
[397] I. Kunce, M. Polanski, J. Bystrzycki, Structure and hydrogen storage properties of
a high entropy ZrTiVCrFeNi alloy synthesized using Laser Engineered Net Shaping
(LENS), Int. J. Hydrog. Energy 38 (27) (2013) 12180–12189, https://doi.org/
10.1016/j.ijhydene.2013.05.071.
[398] I. Kunce, M. Polański, T. Czujko, Microstructures and hydrogen storage properties
of LaNiFeVMn alloys, Int. J. Hydrog. Energy 42 (44) (2017) 27154–27164,
https://doi.org/10.1016/j.ijhydene.2017.09.039.
[399] Y. Qiao, C. Du, J. Tang, P. Jia, X. Zhang, J. Wang, et al., Micron-/nano-scale
hierarchical structures and hydrogen storage mechanisms in a cast vanadiumbased multicomponent alloy, pp. 106588-1–10, Nano Energy 90 (2021), https://
doi.org/10.1016/j.nanoen.2021.106588.
[400] A. Amiri, R. Shahbazian-Yassar, Recent progress of high-entropy materials for
energy storage and conversion, J. Mater. Chem. A 9 (2) (2021) 782–823, https://
doi.org/10.1039/D0TA09578H.
[401] N.K. Katiyar, K. Biswas, J.-W. Yeh, S. Sharma, C.S. Tiwary, A perspective on the
catalysis using the high entropy alloys, pp. 106261-1–9, Nano Energy 88 (2021),
https://doi.org/10.1016/j.nanoen.2021.106261.
[402] W. Dai, T. Lu, Y. Pan, Novel and promising electrocatalyst for oxygen evolution
reaction based on MnFeCoNi high entropy alloy, J. Power Sources 430 (2019)
104–111, https://doi.org/10.1016/j.jpowsour.2019.05.030.
[403] T. Löffler, H. Meyer, A. Savan, P. Wilde, A. Garzón Manjón, Y.T. Chen, et al.,
Discovery of a multinary noble metal–free oxygen reduction catalyst, pp.
1802269-1–7, Adv. Energy Mater. 8 (34) (2018), https://doi.org/10.1002/
aenm.201802269.
[404] C. Cai, S. Guo, B. Li, Y. Tian, J.C.D. Qiu, C. Sun, et al., 3D printing and chemical
dealloying of a hierarchically micro-and nanoporous catalyst for wastewater
purification, ACS Appl. Mater. Interfaces 13 (41) (2021) 48709–48719, https://
doi.org/10.1021/acsami.1c14076.
[405] K.M. Mullin, C. Frey, J. Lamb, S.K. Wu, M.P. Echlin, T.M. Pollock, Rapid
Screening of Single Phase Refractory Alloys Under Laser Melting Conditions, pp.
112726-1–12, Mater. Des. (2024), https://doi.org/10.1016/j.
matdes.2024.112726.
[406] F. Wei, Compositionally graded AlxCoCrFeNi high-entropy alloy manufactured by
laser powder bed fusion, pp. 101308-1–10, Materialia 21 (2022), https://doi.org/
10.1016/j.mtla.2021.101308.
[407] Y. Zhao, K.B. Lau, W.H. Teh, J.J. Lee, F. Wei, M. Lin, et al., Compositionally
graded CoCrFeNiTix high-entropy alloys manufactured by laser powder bed
fusion: A combinatorial assessment., pp. 160825-1–11, J. Alloy. Compd. 883
(2021), https://doi.org/10.1016/j.jallcom.2021.160825.
[408] Z. Liu, B. He, T. Lyu, Y. Zou, A Review on Additive manufacturing of titanium
alloys for aerospace applications: directed energy deposition and beyond Ti-6Al4V, JOM 73 (2021) 1804–1818, https://doi.org/10.1007/s11837-021-04670-6.
[409] V.H.J. Hammond, Equal-channel angular extrusion of a low-density high-entropy
alloy produced by high-energy cryogenic mechanical alloying, Jom 66 (10)
(2014) 2021–2029, https://doi.org/10.1007/s11837-014-1113-x.
[410] B. Li, H. Zheng, C. Han, K. Zhou, Nanotwins-containing microstructure and
superior mechanical strength of a Cu-9Al-5Fe-5Ni alloy additively manufactured
by laser metal deposition, pp. 101825-1–14, Addit. Manuf. 39 (2021), https://doi.
org/10.1016/j.addma.2020.101825.
[411] G. Chen, S. Zhao, P. Tan, J. Wang, C. Xiang, H. Tang, A comparative study of Ti6Al-4V powders for additive manufacturing by gas atomization, plasma rotating
electrode process and plasma atomization, Powder Technol. 333 (2018) 38–46,
https://doi.org/10.1016/j.powtec.2018.04.013.
[412] P. Sun, Z.Z. Fang, Y. Zhang, Y. Xia, Review of the methods for production of
spherical Ti and Ti alloy powder, Jom 69 (10) (2017) 1853–1860, https://doi.
org/10.1007/s11837-017-2513-5.
[413] Y. Jo, W. Choi, D. Kim, A. Zargaran, S.S. Sohn, H. Kim, et al., FCC to BCC
transformation-induced plasticity based on thermodynamic phase stability in
novel V 10 Cr 10 Fe 45 Co x Ni 35− x medium-entropy alloys, Sci. Rep. 9 (1)
(2019) 1–14, https://doi.org/10.1038/s41598-019-39570-y.
[414] Y.H. Jo, J. Yang, W.-M. Choi, K.-Y. Doh, D. Lee, H.S. Kim, et al., Body-centeredcubic martensite and the role on room-temperature tensile properties in Si-added
SiVCrMnFeCo high-entropy alloys, J. Mater. Sci. Technol. 76 (2021) 222–230,
https://doi.org/10.1016/j.jmst.2020.10.038.
[415] S.-X. Li, Evaluation of the effect of grain size on chromium carbide precipitation
and intergranular corrosion of 316L stainless steel, Corros. Sci. 66 (2013)
211–216, https://doi.org/10.1016/j.corsci.2012.09.022.
Asker Jarlöv. Asker Jarlöv is a Ph.D. student supervised by
Prof. Kun Zhou at the School of Mechanical and Aerospace
Engineering, Nanyang Technological University, Singapore. He
received BSc and MSc degrees from Uppsala University, Swe­
den. His research interest lies in additive manufacturing and
computational materials science.
Mui Ling Sharon Nai. Dr. Mui Ling Sharon Nai is the R&D
Director and Senior Principal Scientist at the Singapore Insti­
tute of Manufacturing Technology (SIMTech), Agency for Sci­
ence, Technology and Research (A*STAR). She received her B.
Eng., M.Eng. and Ph.D. degrees from the National University of
Singapore. Her research interest lies in additive manufacturing
of advanced materials and their composites. She also leads both
the Additive Manufacturing Division at SIMTech and the
A*STAR Additive Innovation Centre.
Kun Zhou. Dr. Kun Zhou is a Professor of Mechanical Engi­
neering in the School of Mechanical and Aerospace Engineer­
ing at Nanyang Technological University, Singapore. He
currently serves as Programme Director (Marine & Offshore) in
Singapore Centre for 3D Printing. He received both his B.Eng.
and M.Eng. degrees from Tsinghua University, China and his
Ph.D. from Nanyang Technological University. He has been
conducting multidisciplinary research at the crossroads of
mechanics, additive manufacturing, materials science, and
molecular physics. He is a Fellow of European Academy of
Sciences.
46