Proceedings of ASME Turbo Expo 2018
Turbomachinery Technical Conference and Exposition
GT2018
June 11-15, 2018, Oslo, Norway
GT2018-76686
ADDITIVE MANUFACTURING FOR THE MANUFACTURE OF GAS TURBINE
ENGINE COMPONENTS: LITERATURE REVIEW AND FUTURE PERSPECTIVES
Aboma Wagari Gebisa
Department of Mechanical and Structural
Engineering and Materials Science, University of
Stavanger, Rogaland, Stavanger, Norway
Hirpa G. Lemu
Department of Mechanical and Structural
Engineering and Materials Science, University of
Stavanger, Rogaland, Stavanger, Norway
currently available with completely different processing
methods that use different types of materials, from polymers to
ceramics and metals. The processing methods used in these
technologies are generally categorized into seven different
classes, namely: Vat Photopolymerisation, Material Jetting,
Binder Jetting, Material Extrusion, Powder Bed Fusion, Sheet
Lamination and Directed Energy Deposition [3]. Regardless of
the different processes used in additive manufacturing
techniques, they generally employ similar steps to those listed
below, from the preparation of the computer aided design (CAD)
model to the finishing process:
1. Prepare or design the CAD model
2. Convert the CAD model into a standard tessellation
language (STL) file
3. Slice the STL file into cross-sectional layers
4. Send the sliced model to the machine
5. Build the part (machine)
6. Remove the part from the machine
7. Post-processing, if needed
The AM market is growing very fast in the recent years. A
report by Credit Suisse estimates [4] on AM market trend shown
in Fig 3 is a big evidence for the progress of the technology. The
trends in systems, materials, direct part manufacturing, service
and parts show similar rapid growth of the technology.
ABSTRACT
Additive manufacturing (AM) is an emerging rapid
manufacturing technique that builds parts by tracing their cross
section, layer upon layer. This technology has many unique
capabilities that are not found in conventional manufacturing
techniques. One of these is its ability to produce very complex
part geometries without the need for any tooling. This unique
potential makes it the future manufacturing technique for very
complex and intricate geometries such as gas turbine
components. The current review investigates the available metal
additive manufacturing techniques and materials, in respect of
their applicability for gas turbine engine components. From the
investigation, it is clear that AM is in a promising progress for
the manufacture of aircraft gas turbine components. The current
limitations of AM techniques for the production of gas turbine
engine components are also covered. The future perspective of
this technology in this regard has also been discussed.
Keywords: Additive manufacturing, gas turbine engine,
metallic materials
1.
INTRODUCTION
Additive manufacturing (AM) is a digital manufacturing
technique that has shown dynamic development in recent
decades. This manufacturing method is defined in an ASTM
standard as “a process of joining materials to make objects from
3D model data, usually layer upon layer, as opposed to
subtractive manufacturing methods. Synonyms: additive
fabrication, additive processes, additive techniques, additive
layer manufacturing, layer manufacturing, and freeform
fabrication” [1]. The technology was first patented by Charles
Hull in the late 1980s with Sterelithography Apparatus (SLA) as
a process that solidifies polymeric resin using Ultraviolet (UV)
light [2]. The technology has advanced extensively over the last
30 years, with improvements in many aspects, including
processing techniques and materials. There are many techniques
Fig 1: Global AM market trend
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AM has unique potentials that cannot be realized with
conventional manufacturing techniques. These include their
ability to produce complex geometry, complex multi-material
compositions, hierarchically dissimilar internal structures
(lattice structures) and fully integrated functional components
[5]. In addition, implementation of AM technologies have
numerous advantages, such as mass customization, on-demand
manufacturing, decentralized manufacturing, real design
optimization, etc., over the conventional manufacturing
techniques [6]. Since AM technologies produce parts using
additive processes and guided by the design model, the
technology is able to produce very complex geometries without
the need for any tooling and at no additional cost. With
traditional manufacturing, complex geometric forms that could
increase the performance of the system, such as in aerospace,
automobile and biomedical sectors [7] need to be simplified to
the capability of the processes [8] or expensive tools and fixtures
are needed for the production of these parts. In addition, the
possibilities to fabricate graded material composition [9] for gas
turbine components that are exposed to high thermos-mechanical
loads and repair and remanufacturing of high value components
[10-12] instead of replacing them are among the benefits in the
above-mentioned sectors. It is also reported in [13] that AM is
synergetic with lightweight design and shows promising
progress towards the production of sustainable products,
compared to conventional manufacturing techniques. However,
the implementation of the technology in these sectors, though
attractive, has not been sufficiently explored and reported. Thus,
the aim of this article is to review the available literature in the
area and investigate the research and development potentials of
metallic material-based AM technology in gas turbine
applications.
The article is organized as follows; additive manufacturing
of metallic materials will be discussed in Section 2, with
elaboration on the techniques and materials. Section 3 discusses
the use of AM for the production of gas turbine components,
while Section 4 covers the discussion on the possibilities of
manufacturing gas turbine engine components using AM
technology. Section 5 deals with the limitations of current AM
technologies and materials for the employment of the technology
in this field. In Section 6, the future trends and perspectives of
the technology will be covered and, finally, Section 7 draws
some conclusions.
2.
ADDITIVE MANUFACTURING OF METALLIC
MATERIALS
2.1. Metal Additive Manufacturing Techniques
Metal additive manufacturing techniques represent the core
technology for AM application and the three most applicable
processes for metal printing are Laser Sintering, Laser Melting
and Laser Metal Deposition [7]. The technology, in general can
be classified according to different aspects, including form of
material input, build volume and energy source. In Table 1,
different techniques are classified by their build volumes,
relatively, into small, medium and large. Further categories of
metallic additive manufacturing techniques, based on the form
of metallic materials employed, include:
 Powder bed AM techniques
 Powder feed AM techniques
 Wire feed AM techniques
Table 1. Classification of AM techniques based on their build volume
Size
Small *
SLM 125 (125 x 125 x 125) [14]
EBM Q10 Plus (200 x 200 x 180) [15]
LENS 450 (100 x 100 x 100) [16]
EBM A2X (200 x 200 x 350) [15]
EOS M 100 (⌀100 x 95) [17]
AM
techniques
Medium **
PXL (250 x 250 x 300) [19]
SLM 280 2.0 (280 x 280 x 365) [14]
SLM 500 (500 x 280 x 365) [14]
REALIZER SLM 300i (300 x 300 x
300) [20]
RenAM 500M/ RenAM 500Q (250 x
250 x 350) [23]
Precious M80 (⌀80 x 95) [17]
AM 250/AM 400 (250 x 250 x 300) [23]
Mlab cusing/Mlab cusing R (50 x 50x 80) [18]
EBM Q20 Plus (⌀350 x 380) [15]
EOS M 290/ EOSINT M 280 (250 x 250
x 325) [17]
EOSM 400/ EOSM 400-4 (400 x 400 x
400) [17]
LENS MR-7 (300 x 300 x 300) [16]
M2 cusing / M cusing Multilaser (250 x
250 x 280) [18]
M Line Factory (400 x 400 x 425) [18]
MYSINT300 (⌀300 x 400) [21]
TruPrint 3000 /TruPrint 5000 (⌀ 300 x
400) [22]
DMD IC106 (300 x 300 x 300) [24]
MLab cusing 200R (100x100x100) [18]
M1 cusing (250x250x250) [18]
PXM (140 x 140x 100) [19]
PXS (100x100x80) [19]
REALIZER SLM 50 (⌀70x40) [20]
REALIZER SLM 125 (125 x 125 x 200) [20]
MYSINT100/ MYSINT100 Dual Laser (⌀100
x 100) [21]
TruPrint 1000 (⌀100 x 100) [22]
Large ***
EBAM 68 (1625 x 635 x 1600) [25]
EBAM 88 (2134 x 889 x 1600) [25]
EBAM 110 (2692 x 1194 x 1600) [25]
EBAM 150 (3708 x 1575 x 1575) [25]
EBAM 300 (7112 x 1219 x 1219) [25]
Xline 2000R/ Xline PCG (800 x 400 x
500) [18]
LENS 850-R (900 x 1500 x 900) [16]
IREPA LASER CLAD (1500 x 800 x
800) [26]
DMD 44R (1425 x 1020 x 1020) [24]
DMD 66R (2330 x 1670 x 1670) [24]
* (build volume ≤ 250x250x250 mm3), ** (250x250x250 mm3< build volume≤500x500x500mm3), *** (build volume > 500x500x500mm3)
Note: The dimensions in brackets are all given in mm.
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2.1.1. Powder bed AM techniques
Powder bed additive manufacturing techniques solidify
metal powder, layer upon layer, as illustrated in Fig 1. Once one
layer of a powder from the powder bed is melted by an energy
source, such as a laser beam, the deposited layer gets solidified
by fusing together powder particles. The build piston then moves
down one step (one layer); thus, the next layer of metal powder
is supplied by the powder delivery piston that moves upward and
then the powder is spread by the roller or rake. Then, this powder
layer is again solidified by the laser. This process is repeated until
the part is completed [27]. Some techniques that employ the
powder bed system are Electron Beam Melting (EBM), Direct
Metal Laser Sintering (DMLS), LaserCUSING, Selective Laser
Melting (SLM) and many more [28].
2.1.2. Powder feed AM techniques
Powder feed additive manufacturing techniques build a part,
layer upon layer, like other techniques. Fig 2 shows the building
process of this system, in which the metal powder from the
powder supply source is ejected through the powder feeder into
the substrate. Once the first layer of powder is melted by the laser
beam and solidified, the next layer of powder is spread through
the powder feeder, and this process is repeated until the part is
completed. Laser Cladding (LC), Laser Engineered Net Shaping
(LENS) and Direct Metal Deposition (DMD) are examples of
powder feed AM techniques [28].
Fig 3. Illustration of powder feed AM technique
2.1.3. Wire feed AM techniques
Wire feed AM techniques build parts from metallic wires in
a layer fashion as illustrated in Fig 3. The wire is fed through the
wire feeder to the substrate, on which it is melted by an electron
beam or plasma, based on the specific technique, and solidified.
The technique is believed to be a promising technology for
producing large components with limited complexity [10].
Electron Beam Additive Manufacturing (EBAM) [25] and Rapid
Plasma Deposition (RPD) [29] are key wire feed AM techniques.
Fig 4.Illustration of wire feed AM technique
2.2. Metallic Materials for Additive Manufacturing
Additive manufacturing technology first started with the
utilization of plastic resins; only after a decade did it manage to
fabricate metallic materials additively. As the technology utilizes
different processing methods than those used in conventional
manufacturing technologies, all materials used in the
conventional methods are no longer directly applicable in AM.
Metallic materials are typically hard and strong, with
superior mechanical performance. Due to their superior
properties, metallic materials are employed in different areas of
engineering applications requiring high strength, high tech and
high temperatures. As briefly presented above, metallic materials
are used in different additive manufacturing technologies in a
variety of forms: powder, foil and wire [28, 30]. The metallic
powders are used in two different ways: powder bed and powder
feed. Metallic powders are used in SLM, DMLS, DMD, EBM
and other methods.
Fig 2. Illustration of powder bed AM technique
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Table 2. Overview of available metallic materials for AM processes
Techniques
(process)
Materials
SLM Solutions
(SLM) [14]
Aluminum alloys
AlSi10Mg
AlSi12
AlSi7Mg
AlSi9Cu3
Titanium alloys
Ti6Al7Nb
Ti6Al4V ELI
Titanium Grade 1
Titanium Grade 2
Nickel alloys
HX
INCONEL 625
INCONEL 718
INCONEL 939
Cobalt
chrome
alloys
CoCr28Mo6
SLM MediDent
Tool and Stainless
Steels
15-5 PH
17-4 PH
316L
304
1.2709
Sciaky Inc
(EBAM) [25]
Titanium alloys
Nickel alloys
INCONEL 625
INCONEL 718
Tantalum
Tungsten
Niobium
Stainless Steels (300
series)
2319, 4043 Aluminum
4340 Steel
Zircalloy
70-30 Copper Nickel
70-30 Nickel Copper
EOS
(DMLS) [17]
Aluminum alloys
AlSi10Mg
Cobalt
chrome
alloy
CoCrMo MP1
CoCrMo SP2
Maraging steel
Nickel alloys
HX
INCONEL 625-2
INCONEL 718-6
Stainless steel
17-4PH
CX
17-4 / 1.4542
15-5 / 1.4540
316L
Titanium alloys
Ti6Al4V
Ti6Al4V ELI
Titanium Grade 2
Concept Laser
(SLM) [18]
Aluminum alloys
AlSi10Mg
Cobalt chrome alloy
F75 CoCr
CoCr from Dentaurum
Titanium alloys
Ti6Al4V
Ti6Al4V ELI
Titanium Grade 2
Titanium alloy from
Dentaurum
Nickel alloys
INCONEL 625
INCONEL 718
Tool and Stainless
Steels
1.4404
17-4 PH
1.2709
Stainless HW steal
Bronze
Platinum (950% alloy)
Silver (930% alloy)
Gold
(18
Carat
3N/4N/5N)
Optomec
(LENS) [16]
Aluminum alloy
CP AI
2024
4047
6061
7075
Steel
1018, H13
S7, 17-4 PH
304, 309
316, 410
420
Titanium alloy
CP Ti
Ti-6-4
Ti-6-2-4-2
Ti-6-2-4-6
Ti-48-2-2
Ti 22AI-23Nb
Nickel alloy
IN600, IN625
IN690, IN718
MarM247
Wasp Alloy
Rene 142
Cobalt Alloys
Stellite 21
POM Group
(DMD) [24]
Aluminum alloys
4047
6061
Titanium alloys
Ti6Al4V
CP Ti
Nickel alloys
C-276
INCONEL 625
INCONEL 718
Nistelle C
Wasp Alloy
Cobalt chrome alloys
Stellite 6
Stellite 21
Stellite 31
Stellite 706
Tool and Stainless
Steels
4140 steel
4340 steel
300 Maraging
H13, P20
P21, S 7
420, 316L
15-5 PH
17-4 PH
CPM1V
Invar
Phenix system
(SLM) [19]
Stainless steels
Tooling steels
Non-ferrous alloys
Super alloys
Precious metals
From SINT-TECH
316L stainless steel
Maraging steel
Chrome-cobalt alloy
Irepa Laser
(LC) [26]
Stainless steel
Ti alloys
Ni based alloys
Tool steel
Sisma
(LMF) [21]
Precious
metals
Bronze
Cobalt
Chrome
Stainless
Steel
Maraging
Steel
Nickel alloys
Aluminum
alloys
Titanium
Table 3.Overview of available metallic materials for AM processes
Techniques
(process)
Materials
ARCAM
(EBM) [15]
Titanium alloys
Ti6Al4V
Ti6Al4V ELI
Titanium Grade2
Cobalt-Chrome
alloys
ASTM F75 CoCr
Nickel alloys
INCONEL 718
Renishaw
(SLM) [23]
Aluminum alloy
AlSi10Mg
Cobalt chrome alloy
Maraging steel
Nickel alloys
INCONEL 625-2
INCONEL 718-6
Stainless steel
316L
Titanium alloys
Ti6Al4V
Norsk Titanium
(RPD) [29]
Titanium alloy
Ti6Al4V
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Among AM techniques that employ metallic materials in a wire
form is EBAM technology. The system employs different
metallic materials, such as titanium and titanium alloys, nickel
alloys, tantalum, tungsten, niobium, stainless steels, aluminum
alloys, zirconium alloys and copper nickel alloys, in a wire form
[25]. The other system that employs titanium alloy ( Ti6Al4V) in
a wire form is RPD.
3.
mostly extreme requirements that lead to very complex part
geometries, as performance increases with complexity [34].
Furthermore, since most gas turbine engine components
(compressor and turbine blades, nozzles) are very complex in
geometry [33], their production could easily be realized with the
implementation of AM techniques. The airfoil shape of turbine
blades, for instance, requires a special geometry that is designed
for the aerodynamic performance. Small deviations in the shape
can have large consequences in its performance and hence
control of the airfoil shape is a critical design step [11]. In
addition, when complexity increases, it creates challenges for
conventional manufacturing techniques, as complex parts
require the assembly of individual parts with nuts, bolts, rivets
and welds, thus reducing the reliability of the component. On the
other hand, AM technology provides the designer with greater
design freedom and facilitates the production of complex part
topology that cannot be produced with the existing
manufacturing techniques, as there are few or no limitations on
how much complex topology to produce [8, 13]. Therefore,
design optimization can be used to reduce the weight of engine
parts, by modifying their topology, while maintaining their
functional requirements and improving their performance.
Production of a sustainable product is another primary
requirement in many sectors such as the aerospace and the
automobile industries. The choice of production technique plays
a great role in making the production of components more
sustainable. Although only limited research [35-37] has been
reported on the assessment of the sustainability of AM
technologies, there are indications that the technology is in a
promising trend for the production of sustainable products,
compared to conventional manufacturing techniques. Therefore,
although further investigations are required for the assessment,
it seems that AM technology is advancing a preferable
production technique for the realization of sustainable aerospace
products.
WHY ADDITIVE MANUFACTURING FOR GAS
TURBINE ENGINE COMPONENTS?
AM technologies produce parts, layer upon layer, by tracing
their cross section directly from a 3D CAD model. As mentioned
in the introduction section, the technology has plenty of
advantages over conventional manufacturing techniques,
including production of functionally integrated products,
efficient use of materials, where needed, its synergy with optimal
design of complex geometric forms and the sustainability of the
manufacturing technique. This section discusses these
advantages of AM technology that make it a promising
production technique for producing gas turbine engine
components.
The production of a fully integrated product is among the
advantages of AM. Fully integrated functional devices, not just
individual piece-parts, can be produced in one build, as the
technology permits the consolidation and functional integration
of parts [31]. Functional integration of parts reduces the number
of parts, thus reducing the challenges encountered during the
assembly process [5]. This could be essential for gas turbine
engine components, as it could allow the production of a
completely assembled compressor or turbine at a much lower
price. A report [32] shows that the utilization of additive
manufacturing with other new technologies enabled designers,
engineers and materials experts to combine 855 individual
components into just 12 parts, reduced the weight of the engine
by more than 45kg, improved the fuel burn by almost 20%, gave
the engine 10% more power and simplified the maintenance for
a new advanced turboprop engine.
In the aerospace industry, buy-to-fly ratios are
approximately 20:1; i.e., 100kg of input material is needed to
produce 5kg of the final product [33]. This means the remaining
95kg of material is waste, requiring reprocessing or recycling.
This is because many gas turbine engine components must
satisfy exceptional requirements [34]. However, since AM
technology produces parts by adding cross sections of a part,
layer upon layer, it reduces waste or has no waste. Therefore,
AM could reduce the amount of waste and thus reduce the cost
of gas turbine engine components’ production by order of
magnitudes.
The synergetic behavior of AM with optimal design is
another advantage. Design optimization is a powerful design
approach to save time, material and energy. Although it started a
long time ago with consideration of the existing conventional
manufacturing techniques, the existing manufacturing
techniques did not benefit very well from this design approach
because there are manufacturing constraints for producing the
optimized design. For gas turbine engine components, there are
4.
AIRCRAFT GAS TURBINE ENGINE COMPONENTS
Gas turbine engines can be categorized into aircraft gas
turbine engines, heavy-duty gas turbine engines and light
industrial gas turbine engines. The scope of this paper is limited
to aircraft gas turbine engines that are critical aircraft
components to generate power for driving the whole aircraft
[38]. Fig 4 [39] shows the engine components with their
respective temperature, pressure and velocity profiles. From the
figure, it is clear that the pressure increases from the inlet to the
low-pressure compressor. However, from the inlet of the highpressure compressor, it increases drastically. Whereas the
temperature and velocity increase sharply from the inlet to the
outlet of the combustion chamber from around 700°C to close to
1350°C, as Fig 4 shows, the flame temperature in the combustion
chamber can reach above 2000°C. The temperature decreases
from the turbine inlet to the outlet, and even at the turbine outlet
it is above 1000°C. The following subsections will discuss the
available metallic AM materials used for these main engine
components and analyze the current state of AM technologies for
production of these components.
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Fig 5. (Top) Rolls-Royce Conway gas turbine engine system and (Bottom) Temperature, pressure and velocity profile of gas turbine
engine system
4.2. Combustion Chamber
Combustion chambers are the parts of a gas turbine engine
where the fuel and air mix is burned. As can be seen from Fig 4,
the working temperature of this part is higher than that of the
high-pressure compressors. Therefore, the materials to be used
for this part must sustain this high temperature and the creep at
this high temperature. For this reason, nickel-based super alloys
have come to play the role. Among the materials used for the
combustion chamber, Hastelloy X and Inconel 718 nickel alloys
[40] are available in metallic materials for AM (see subsection
2.2). These two materials, Hastelloy X and Inconel 718, can be
used for the flame tube and casing of the combustion chamber,
respectively [42], due to their high creep strength and corrosion
and oxidation resistance. Either functionally graded material
printing or a thermal barrier coating that can improve the
performance of the combustion chamber can also be
implemented by cold spraying; that is becoming an additive
manufacturing technique [43].
4.1. Compressor
Compressors are the parts of an engine responsible for
providing enough air with enough pressure to the combustion
chamber. In most gas turbine engines have two compressors:
low-pressure and high-pressure, which operate at different
working temperatures (Fig 4). The low-pressure compressor
usually works at relatively low temperatures, around 350°C,
whereas the high-pressure compressor works at temperatures
above 500°C to 600°C. For functional effectiveness, the
compressor must be made from materials that can sustain these
moderately high temperatures and pressures.
Among the materials used for these components, titanium
alloys, such as Ti64, Ti6242 and Ti6246, are widely used due to
their high strength to weight ratio [40, 41]. As detailed in Section
2.2, these materials are available metallic materials for AM. AM
technologies such as SLM, EBM, RPD, LENS and others do
support fabrication of Ti64 and Ti6246 materials and hence these
processes could be employed for the production of low-pressure
compressor discs and blades because of the material’s ability to
sustain high temperatures of about 325°C and 450°C,
respectively [41]. Furthermore, for the high-pressure compressor
parts, a LENS AM system can be employed, since it is the only
system that supports Ti6242 material, which can sustain a
temperature of about 540°C [16, 41].
4.3. Turbine
The turbine is the part of the gas turbine engine that receives
the hot air from the combustion chamber and expands it to the
outside. As the air that comes into the turbine is at high
temperature, turbine materials must sustain this. Because of the
stresses of this high temperature on the turbine blades, turbine
materials become damaged through creep mechanisms, thermal
fatigue and environmental attack [44, 45]. To overcome the
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creep, thermal coatings and super alloys are used in turbine blade
designs. For turbine discs, among the metallic materials
available for AM, Inconel 718 can be used because of its high
creep strength; most AM techniques [14-18, 23, 25] use this
material. The fact that turbine blades have very complex shapes
and are primarily vulnerable to high-temperature operation
means that high-performance materials with special
manufacturing routes are used [40]. Among the available AM
metallic materials, Rene 142 could be employed for turbine
blades, as it has superior high temperature performance [46, 47],
with LENS [16] because it is the only technique that supports
this material.
5.
The other important issue to be raised at this point is that SLM
additive manufactured metallic parts are suffering with inferior
mechanical properties, resulting from early cracking, due to the
residual stresses caused by the rapid cooling nature of the process
[50-52]. However, during recent years, interesting developments
have been seen in this area: by optimizing the processing
parameters of the systems [52], the mechanical properties of
additively manufactured parts are becoming more comparable to
those produced with conventional manufacturing techniques. In
addition, post processing, such as heat treatment and finish
machining [48], can alleviate these problems. There are also
systems like EBM that work under a vacuum environment,
which minimize the issue of residual stresses [53]. Moreover,
further investigations are needed to develop a standardized
processing method for each of the techniques, to achieve the
desired level of mechanical performance of the parts.
LIMITATIONS OF ADDITIVE MANUFACTURING
Additive manufacturing technology is improving over time
and becoming a promising manufacturing technique. The
implementation of this manufacturing technique for gas turbine
components’ production can be realized if the general limitations
discussed elsewhere [48, 49], in addition to those listed below,
are overcome.
In Section 2, different categories of AM manufacturing
techniques were presented, based on different aspects. Gas
turbine engine components have different size ranges, according
to their specific application areas. Based on the size of the gas
turbine engine components, these AM technologies could be
applied. Among the size-based categories, most techniques are
in the range of small to medium, while large AM techniques
account only around 25%. Moreover, the large AM techniques
only support a limited variety of materials, though they are not
detailed in this article.
In Section 2, metallic materials available for different AM
techniques are discussed. From the lists of materials in Tables 2
and 3, only a few are applicable for gas turbine engine
components. In addition, an overview of eligible metallic
materials for gas turbine engine components is reported in [40].
Furthermore, among the list of eligible materials, very limited
types of materials such as titanium-based alloys and nickel-based
alloys currently available. In this regard, much effort is needed
for new materials so that the application of AM technologies can
be realized in different engineering applications, including the
production of gas turbine engine components.
AM is a powerful manufacturing technique that can produce
very complex shapes, such as compressor and turbine blades,
with little or no material waste. Moreover, specifically, the
production of turbine blades could be advantageous if a
manufacturing technique that can produce single crystal or
directionally solidified blades is used. This is because the failure
of turbine blades is mainly caused by the nucleation and growth
of cavities along grain boundaries; if the transverse grain
boundaries are eliminated through manufacturing, the failure
probabilities can be effectively reduced [40]. This is because the
parts can exhibit superior creep properties and improved
operation temperatures. Therefore, for different AM techniques,
capability of producing single crystal, and/or directionally
solidified parts and intermetallic alloys need to be developed.
6.
FUTURE TRENDS
AM techniques and materials for AM development have
improved over the last three decades. These progresses are
mainly to make the technique a promising manufacturing
technique, especially for the production of very complex parts.
The technology can be realized as an alternative production
method for gas turbine components, if it maintains the current
pace as discussed below.
As discussed in the previous section, regarding the
implementation of AM for the production of gas turbine
components, the technology currently has some limitations. The
print size is one of the critical limitations of AM machines. For
most of the systems, the largest part size that can be produced is
in the small and medium range of about 0.125 m3 in volume.
From Table 1, it can be seen that one fourth of the systems are in
the large size category. If the current advances in AM techniques
proceeds, however, the print size problem can be solved in the
near future, and many large-capacity systems could be realized.
The availability of materials that are suitable for the
production of gas turbine components is another limitation to
current AM techniques realizing the production of these
components. If the development of materials, intermetallic
alloys, oxide dispersion strengthening (ODS) alloys and other
super alloys eligible for the production of these components is
advanced from the side of both the machines’ manufacturers and
the metallurgical companies, it is foreseen that AM technology
will be the future method for producing components for gas
turbines. Moreover, the availability of materials for large AM
techniques is also limited, and much work is needed to develop
new materials that are suitable for large AM machines to produce
gas turbine engine components, using these techniques.
The AM technique is paving the way for the production of
complex multi-material compositions. This potential of the
technique also opens the door for the production of intermetallic
alloys, as they have high-temperature creep resistance and are
lightweight compared to nickel-based alloys. Murr et al. [54]
have reported the possibility of producing titanium aluminide (γTiAl and γ/α2-Ti3Al) alloys, using EBM additive manufacturing.
7
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ABBREVIATIONS
Additive Layer Manufacturing using Gas Tungsten Arc Welding
was also proposed as an alternative manufacturing technique for
the production of titanium aluminide (γ-TiAl) alloy by in situ
alloying of two wires: titanium and aluminum [55].
The development of ODS alloys on the surface of super
alloys using AM techniques [56-58] is also another promising
development, as ODS alloys are advanced high-temperature
materials for nozzles and vanes, which can retain useful strength
up to a relatively high fraction of their melting point. This is due
to the uniformly dispersed, stable oxide particles, which act as
barriers to dislocation motion. These advancements in the
technology could make the production of complex parts feasible
at a low price. Different researchers have invented and patented
methods that can be used for the production of single crystal gas
turbine blades, repairing them using additive manufacturing [12;
59-63]. If these methods are commercialized and realized in the
coming years, it will be a breakthrough for the production of gas
turbine engine components. This is because single crystal parts
have no grain boundaries, so failure due to the crack initiation
and growth from the grain boundaries is avoided.
7.
Abbreviations
ALM
AM
CAD
DMD
DMLS
EBAM
EBM
GTAW
IT
LC
LENS
LMF
ODS
RPD
SLA
SLM
STL
UV
CONCLUSIONS
This review revealed that AM technology is advancing in
both techniques and material development. The technology has
many advantages that make it the future manufacturing
technique for aerospace components. Although the technology is
not yet matured and there are many challenges and limitations to
be overcome, it shows a promising trend for the realization of the
technology in different areas, including gas turbine engine
components production. It can also be clearly stated that, even
though only a few available materials that are suitable for gas
turbine engine component production, the developments in this
area during recent years show the constructive progress of the
technology. Despite the fact that size, material type and
production capability limitations of AM techniques still remain,
the technology has immense contributions in the necessary
transformation to digital manufacturing, which suites well for
optimized design. This has an obvious benefit for improved
performance of systems with complex geometry such as in gas
turbines.
Spelled-out version
Additive Layer Manufacturing
Additive Manufacturing
Computer Aided Design
Direct Metal Deposition
Direct Metal Laser Sintering
Electron Beam Additive Manufacturing
Electron Beam Melting
Gas Tungsten Arc Welding
Information Technology
Laser Cladding
Laser Engineered Net Shaping
Laser Metal Fusion
Oxide Dispersion Strengthening
Rapid Plasma Deposition
Stereolithography Apparatus
Selective Laser Melting
standard tessellation language
Ultraviolet
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