j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
Available online at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/jmrt
Original Article
Effect of manganese and homogenization on the
phase stability and properties of CueAleBe shape
memory alloys
Bala Narasimha Guniputi a, Murigendrappa S.M. b,*
a
b
School of Engineering, Malla Reddy University, Hyderabad, 500100, India
Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal, 575025, India
article info
abstract
Article history:
In this study, the effect of addition of manganese to the ternary CueAleBe shape memory
Received 7 May 2021
alloys on phase stability, phase transformation temperatures, microstructure, morphology
Accepted 8 July 2021
and grain size has been investigated. Secondly, the effect of betatization temperatures and
Available online 21 July 2021
time period has been investigated on the phases and properties of CueAleBeeMn SMAs.
Results reveal that the addition of manganese in the alloys with Al 11.8 wt.% forms
Keywords:
coexistence of b01 and g01 martensites, and manganese 1 wt.% forms austenite b1 (DO3).
Shape memory alloys
DSC studies exhibit two stage reverse transformation attributes to coexistence of mar-
CueAleBe
tensites. Increase in manganese decreases the transformation temperatures and increase
Manganese
in betatization temperature and time increases transformation temperatures. Alloying
Thermal treatment
manganese didn't exhibit significant grain refinement and results reduced shape recovery
Phase transformation
due to the coexistence of martensites.
Two stage transformation
© 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC
BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1.
Introduction
CueAleBe shape memory alloys (SMAs) are considered as
prime alternative to NieTi SMAs in low and intermediate
temperature applications [1] due to their good shape recovery, pseudo-elasticity [2], damping, thermal stability, and
very economical [3]. Besides, CueAleBe alloys have a prime
limitation, i.e., intergranular/brittle failure happens in a
shorter functional life attributed to coarse grains as happens
in CueAl, CueAleNi and CueZneAl SMAs. CueAleNi SMAs
with 14.5 ± 1 wt.% of Al and 3.5 ± 1 wt.% Ni also exhibits
transformation temperatures around the room temperature,
but these alloys are not extensively used in applications
because of the increase in concentration of Al and Ni forms
g2 particles at the grain boundaries embrittles the alloy and
prevents martensite transformation. Grain boundary
embrittlement leads to rapid failure and reduction in functional life.
It is learned from the literature, Matushita et al. [4] investigated addition of Mn to binary CueAl alloys improved
ductility, and Kainuma et al. [5] observed addition of Al in
lower concentrations enhances ductility owing to the
decrease in degree-of-order. Addition of Mn as quaternary
element to CueAleNi SMAs exhibit magnificent improvement
* Corresponding author.
E-mail address: smm@nitk.ac.in (M. S.M.).
https://doi.org/10.1016/j.jmrt.2021.07.027
2238-7854/© 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
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j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
Fig. 1 e Schematic illustration of preparation of CueAleBeeMn SMAs and betatization treatments for specimens.
in strength [6], super-plasticity [7], thermoelastic and pseudo
elastic properties [8] and functional life [9]. Literature unveils,
no detailed investigation reported on the effect of Mn to
CueAleBe SMAs and also the effect of betatization temperature and duration on the phase stability and properties, and
this stimulates to investigate the effect of variation of
wt.% of Mn on the microstructure, phases, transformation
temperatures, and shape recovery of the alloys in the current
study.
2.
Materials and methods
a) Preparation and betatization of SMA:
In this study, two CueAleBe SMAs of nominal compositions of Cu87.75eAl11.80eBe0.45 and Cu87.5eAl12.00eBe0.45 alloyed
with manganese (Mn) in the amounts, i.e., 0.1, 0.2, 0.3, 0.5 and
1.0 wt.%, were prepared. Fig. 1 illustrates the steps involved in
j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
preparing the SMAs and the different betatization treatments
for the SMAs. Table 1 presents the actual composition of the
SMAs, and the elemental composition varies from the nominal composition due to volatilization losses. Betatization
treatment of 850, 900 C at 15 and 30 min was given only for
M1eM5. SMAs are designated as “MXY” where X ¼ 1,2,3,4, …., 10
represents type of alloy (Table 1) and Y ¼ A,B,C,D represents
betatization temperature and duration i.e., 850 C/15 min,
850 C/30 min, 900 C/15 min and 900 C/30 min respectively,
and the same is shown in Fig. 1.
b) Characterization:
Initially, the betatized and quenched SMA specimens were
mechanically polished to thickness of 0.5 mm. The polished
specimens were studied for phases and crystal structure using
X-Ray Diffractometer. The phases, martensite variants and
sub-structure of the SMAs are confirmed from the selected
area diffraction patterns (SAED) and bright field images (BFI)
using High Resolution Transmission Electron Microscope
(Make: JEOL Model: JEM 2100). Thin foils for TEM analysis were
prepared as follows: the specimens of thickness 0.5 mm used
for XRD studies was mechanically polished to 0.1 mm and
then finely polished into a foil of ~40 mm thickness, and the
foils are punched into the form of discs of 43 mm using Disc
Punch. The disc specimens are perforated at 5 kV using argon
ion-milling. Observations were carried out using a single-tilt
specimen stage operated at 200 kV. Also, the polished specimens were studied for microstructure and morphology utilizing optical microscope. Grain sizes of the alloys were
determined from the optical micrographs using ASTM E 1382.
Phase transformation temperatures of the SMAs were
measured using differential scanning calorimeter at a scanning rate of 2 /min. Shape recovery ratio (SRR) was measured
by the bend test [10].
3.
Results and discussion
3.1.
XRD e phases
Fig. 2 presents the X-ray diffractograms of the SMAs betatized
at “A” and water quenched (Fig. 1). From the diffractograms, it
is observed that SMAs M1A, M2A, M3A, M4A, M5A, M6A, M8A
possess a mixture of b01 e 18R and g01 e 2H variants, i.e.,
Table 1 e Actual composition of alloys (wt.%).
S. No
Alloy
Cu
Al
Be
Mn
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
M1
M2
M3
M4
M5
M6
M7
M8
M9
M10
87.55
87.36
87.32
87.12
86.69
87.24
86.99
87.02
86.71
86.42
11.90
12.00
11.90
11.90
11.90
12.20
12.30
12.20
12.30
12.10
0.43
0.41
0.45
0.43
0.41
0.43
0.43
0.41
0.41
0.42
0.12
0.23
0.33
0.55
1.00
0.13
0.28
0.37
0.58
1.06
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coexistence of martensites (b01 þ g01 ). SMAs M7A, M9A and M10A
are of pure austenite (b1 e DO3).
Literature presents that rapid quenching of CueAleX
(X ¼ Ni, Mn, and Be) SMAs from high temperature “b” (A2)
phase to room temperature forms metastable phase “b1 ” (DO3)
austenite or b01 (18R) and g01 (2H) martensites, depends on wt.%
of Al and ternary element. Fig. 3 presents the binary CueAl
phase diagram, and exhibits complete martensite of b01 (18R)
and g01 (2H) variants below 100 C and in between 11.8e12.2
and 13e14 wt.% of Al respectively. It is worth noting that
coexistence of martensites (b01 þ g01 ) occurs in a narrow
composition range, i.e., 12.2e13 wt.% of Al (Fig. 3).
In the present investigation, coexistence/mixture of martensites forms in the SMAs comprises wt.% of Al in between
11.9 and 12.3, which is lower than CueAl binary alloy as discussed in the preceding paragraph. It is worth noting that
addition of manganese to ternary CueAleBe SMA shifts the
domain of mixture of martensites (Fig. 3) to lower Al concentration as seen in ternary CueAleMn system [11] (Fig. 4). Alloys with increased addition of Be [1] lowers the eutectoid
region and forms the metastable phase b1 e DO3 lower than
the CueAl binary system. The coexistence of martensites also
observed in CueAleNi [12] and CueZneAleNieMn [13] SMAs
dependent on the elemental composition and the quenching
medium temperature.
The salient observations from the XRD analysis are as
follows:
(i) Addition of 0.1 wt.% of Mn to ternary CueAleBe SMA
with 11.9 Al, 0.43 Be [14] in M1 exhibit the mixture of
martensites. In contrast, ternary SMA with same
elemental composition exhibit complete b01 martensite.
(ii) SMAs with 0.55 wt.% of Mn forms coexistence of b01
and g01 , and >0.55 wt.% of Mn forms metastable
austenite “b1 ”.
(iii) Besides, SMAs M7 M9 and M10 exhibits pure austenite of
DO3 order compared to M2, M4 and M5 due to the
increased addition of Al and Be lowers the eutectoid
region.
(iv) Minor change in wt.% of Be didn't exhibit phase and
martensite modification and Mn plays a significant role
in the modification of phases followed by Al and Be.
3.2.
Microstructure and morphology
Fig. 5 shows the microstructures of betatized and quenched
CueAleBeeMn SMAs, and it is evident that the grains are
coarse and bimodal. Increase in Mn didn't exhibit significant
grain refinement [7], and increase in betatization temperature
and duration increases the grain size. The average grain size
of the SMAs are 537.25 ± 10, 470.35 ± 13, 547.27 ± 20,
524.26 ± 16, 460.28 ± 13, 590.23 ± 13, 573.65 ± 13, 327 ± 20,
582.64 ± 11 and 593.28 ± 13 mm for M1, M2, M3, M4, M5, M6, M7,
M8, M9 and M10, respectively. Microstructures reveals that
SMAs consists mixture of very thin and coarse martensite
plates at different locations and orientations. Martensite
plates in the form of clustered thin and sharp needles in zigzag configuration is b01 , and martensite plates is in the form
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j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
Fig. 2 e X-ray diffractograms of a) M1A, M2A, M3A, M4A and M5A b) M6A, M7A, M8A M9A and M10A.
of thick plates is g01 . TEM analysis were performed on SMAs to
confirm the type of martensite variants as studied from XRD
and microstructures. Bright field images and Selected Area
Electron Diffraction patterns were obtained at different regions of SMA using HRTEM. SAED patterns are indexed using
“Crystbox” [15] Fig. 6a presents the bright field micrograph
Fig. 3 e CueAl phase diagram e adopted and modified [19].
with very thin and narrow martensite plates and its corresponding SAED pattern in Fig. 6b confirms b01 martensite
[16,17] configuration Fig. 6c presents the bright field
Fig. 4 e Pseudo binary phase diagram of CueAleMn e
adopted and modified [11].
j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
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Fig. 5 e Microstructures of CueAleBeeMn SMAs at 50£.
micrograph with parallel and coarse plates and its corresponding SAED pattern in Fig. 6d confirms g01 martensite of 2H
configuration. Thus, it is confirmed that the SMAs possess
coexistence of martensites. Besides, SMAs M9 and M10 exhibits
pure austenite of DO3 order confirms from the X-ray diffractograms (Fig. 1).
3.3.
DSC e phase transformation temperatures
Fig. 7 depicts the thermograms of the water quenched
CueAleBeeMn SMAs. Increase in wt.% of Al, Be, and Mn decreases the transformation temperatures. Alloys M1, M3, M4,
M5, M6 and M8 exhibit two endothermic peaks represents two-
Fig. 6 e Bright Field Transmission Electron Micrographs of M4A (a) 18R martensite (c) 2H martensite and corresponding Select
Area Electron Diffraction Patterns (SAED) (b) 18R martensite taken along [010] axis. (c) 2H martensite taken along [293] axis.
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j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
Fig. 7 e Thermograms of CueAleBeeMn SMAs at
betatization A.
stage reverse transformation, whereas M2, M7, M9, and M10
exhibit only one endothermic event representing a singlestage reverse transformation. Two stage reverse transformation is due to the coexistence of martensites [12,13]. The
first endothermic peak (Fig. 7) in the lower temperature side
represents the transformation of b01 /b1 and the second
endothermic peak in the higher temperature side represents
the transformation of g01 /b1 . Single stage transformation i.e.,
b01 þ g01 /b1 , attributes to the existence of only b01 martensite or
b1 austenite in the SMAs as discussed in sec 3.1 and 3.2. It is
Fig. 8 e Thermograms of M1, M2, M3, M4 and M5 M1A SMAs
betatized at A, B, C and D.
also observed that, no interval/gap in transformation between
b01 /b1 and g01 /b1 , and the size and shape of the peaks describes the enthalpy required for reverse transformation.
Fig. 8 presents the thermograms of betatized and water
quenched CueAleBeeMn SMAs at betatization temperatures
of 850, 900 C for 15 and 30 min. It is observed from the
endothermic events of M1A,B,C,D SMAs is that M1A exhibits twostage reverse transformation, in contrast M1B, M1C and M1D,
exhibits single stage transformation. Thermograms of
M2A,B,C,D SMAs presents that M2A and M2B exhibit transformation in single step whereas in M2c and M2D exhibits two
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j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
steps attributes to coexistence of martensites as confirmed
from XRD and microscopy. It is worth noting that the endothermic event 2 of M1B, M1C, M1D, M2A and M2B is broader as
compared to rest of the betatized SMAs in their respective
group. Broadening of the peak is due to the mixture of two
peaks into one i.e., the transformation temperature As2 of the
SMAs starts at ~32 C and ~61 C for M1A,B,C,D and M2A,B,C,D
respectively. Thus, it is to be said that these alloys exhibit
mixture of martensites.
Thermograms of M3A,B,C,D, M4A,B,C,D and M5A,B,C,D displays
that all the SMAs exhibit two stage transformation. It is also
observed that from the thermograms (Fig. 8) the transformation temperatures Mf1, Ms1, As1, Af1, As2 and Af2 increases with increase in betatization temperature and
duration.
3.4.
Shape recovery ratio
The prepared SMAs were hot rolled at 800 C into a sheet of
thickness 0.5 mm, and each SMA sheets are betatized at
850 C, 900 C for 15 min and 30 min and quenched directly
into water at room temperature (Fig. 1). Shape recovery ratio
of the SMAs were investigated experimentally by bend test
(Fig. 9). The quenched sheets are bent around a mandrel
(deformed) and then unloaded, viz. from AeA to AeB, this
angle measured as qd . The deformed MXY SMA sheets are
heated at the temperature Af þ 10 C as shown in the thermograms, and it tends to attain the original position with or
without residual strain, i.e., AeC or AeA, respectively, this
angle measured as qr .
The shape recovery ratio computed using Eq. (1).
qd qr
h¼
qd
(1)
where qd e angle after deformation andqr e residual angle
after recovery.
The recovery ratio of each SMA were calculated using Eq.
(1) and tabulated in Table 2. It is observed that increase in
addition of manganese decreases shape recovery, and increase in betatization temperature and duration further
Table 2 e Shape recovery ratio of the MXY SMAs.
M1
M2
M3
M4
M5
M6
M7
M8
M9
M10
A
B
C
D
83
81
82
79
76
81
Austenite (RT)
80
Austenite (RT)
Austenite (RT)
80
77
78
78
74
e
62
58
56
57
54
e
59
54
52
41
43
e
e
e
e
reduces the recovery of the SMAs and stabilized. The reduction in shape/strain recovery attributes to (i) Increase in
addition of Mn shifts the domain of coexistence of martensites to lower side of Al as discussed in sec 3.1, which increases
the proportion of coexistence of martensites in the SMAs
causes lattice mismatch/disorder [18] (ii) Increase in manganese and betatization temperature increases the width of 2H
martensite plates (Fig. 6) and random orientations (Fig. 5)
restrict the martensite plate movement (iii) Broader endothermic peak i.e., g01 (2H) lags in transformation requires
additional energy for the reverse transformation as compared
to b01 and the same can be seen from the thermograms attributes to the coarser martensite plates.
4.
Conclusions
Effect of addition of manganese and betatization at 850 C,
900 C for 15 and 30 min were studied on the phase stability,
microstructure, transformation temperatures and shape recovery ratio of CueAleBe polycrystalline shape memory alloys. The conclusions drawn from the investigation are as
follows:
Addition and increase in manganese didn't exhibit significant grain refinement.
Fig. 9 e Schematic of bend test for shape recovery ratio.
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j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 4 : 1 5 5 1 e1 5 5 8
Manganese with 0.55 wt.% and Al 11.8 wt.% forms
coexistence of b01 and g01 martensites in both eutectoid and
hypo eutectoid Al SMAs.
Addition of Mn > 0.55 wt.% to eutectoid and hyper eutectoid Al SMAs exhibit pure austenite of DO3 order.
Addition and increase in manganese decrease the transformation temperatures. SMAs with coexistence of martensites exhibit two stage reverse transformation.
SMAs exhibit maximum recovery of 83%, and SMAs with
coexistence of martensites are not suitable for rapid
response (recovery) applications.
Declaration of Competing Interest
The authors declare that we have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
Acknowledgement
This study is financially supported by the Department of Science and Technology, Government of India, under Project No:
EMR/2016/001247.
Authors would like to express their gratitude to Prof.
Miloslav Klinger, Institute of Physics of the Czech Academy of
Sciences for providing the “Crystbox” Tool for indexing the
SAED patterns.
Authors would like to thank Dr. K. Jeyadheepan, Sastra
Deemed University for the support in SAED indexing.
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