**1. Introduction**

Aerospace engine components are exposed to high temperatures as a result of enormous heat generation in the engine and formation of large temperature rise across the structural parts. These components are generally expected to possess a high strength-to-weight ratio in order to give high thrust, improved fuel efficiency at minimal fuel consumption while increasing speed of flight. Aircraft engines are usually fabricated by titanium alloys, nickel-based super alloys, superior steels or ultrahigh-temperature ceramics. Moreover, an important engineering material for manufacturing of gas turbine and aircraft engine components are alloys of titanium (Ti) because of good properties like corrosion resistance, excellent specific strength and most especially their low density [1]. Also, due to the biocompatibility of these alloys, they have been applied in biomedical industries as implants [2–4] and prosthetic beak [5]. The poor wear performance and low hardness of titanium alloys constrained their adoption in fabricating components to be subjected in contact forces of friction and wear [3, 6]. Likewise, titanium alloys have not been impressive for load-bearing components (LBC) in the aerospace industry because of uneven stress distribution on parts [7].

of 48 at.% Al generally comprise of a γ-phase and α2-phase with L1o and DO19 structure respectively (major: γ-TiAl, minor: α2-Ti3Al) typically referred to as γ-TiAl [10, 24]. This γ-TiAl-based alloy are continuously been improved upon in the manufacturing nozzles, low pressure turbine blade (LPTB) and turbochargers in

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based…*

General Electric has applied the Ti48Al2Cr2Nb alloy called the GE4822 to manufacture the Boeing-787 Dreamliner's engine known as GEnx-1B that reduces both fuel consumption and CO2 emission by 15% [11, 21, 26]. Due to the GE4822 alloys high-temperature capability, there has been works on improving the ductile property of γ-TiAl which have been used for low-pressure turbine (LPT) blades [11, 16, 18, 27] and to expand the temperature range 800–850°C [11]. High Nb-containing TiAl known as TNM have been produced with higher yield strength, oxidation resistance and better creep than conventional TiAls [15, 19, 23, 26, 28, 29].

However, the extremely poor tensile ductility (<1% elongation) of TiAl-based alloys at room temperature, poor fracture toughness and high-temperature poor workability makes it difficult to fabricate and strongly limits their applications in the industry [10, 13, 15, 16, 18, 30]. This has made conventional processing techniques very problematic in manufacturing TiAl-based components. Hence, a lot of interest in improving the ambient temperature characteristics and oxidation resistance at elevated temperature, methods such as alloying and post-processing heat

treatment has been suggested to help advance its properties.

materials (FGMs) which are difficult to produce [33, 34].

**2. Additive manufacturing (AM)**

**195**

Apart from the potentially improved geometrical complexity, additive manufacturing (AM) permits manufacturing of innovative materials with functionally graded capabilities during fabrication [14]. The applicability of TiAl alloys is becoming more progressive due to the growing knowledge of the connections concerning mechanical properties and microstructural evolution as well as modifications in processing operations [18]. However, even with AM technologies issues of the mass production quantities is still not making the technique cost-effective [31]. Currently, AM has gained acceptance for manufacturing customized products with complex geometrical freedom, more homogeneous microstructure and functionally enhanced parts gradually replacing traditional processes [14, 28, 32]. Due to this property, it is possible to manufacture components and finished parts which could not be implemented with conventional manufacturing technologies or only at great expense. AM routes is poised to produced γ-TiAl parts for aerospace applications. Laser additive manufacturing (LAM) is a class of AM process that makes use of

high-powered laser beam in melting and fabricating metal powders into threedimensional (3D) components from a predesigned computer-aided design (CAD) model. One of the highly desirable LAM techniques is laser engineered net shaping (LENS®) regarded for producing ceramics, composites and functionally graded

The objective of this work is to give an overview of LAM of TiAl alloys and composites while presenting a review of crucial matters, investigation tendencies, fabrication and progress achieve on γ-TiAl based materials for aerospace. A succinct overview of TiAl was first presented followed by AM of titanium alloys particularly those applied in aerospace industries. The paper subsequently highlights a comprehensive appraisal of latest studies on γ-TiAl laser processing and post-processing effects on microstructural evolution and mechanical properties. Prospects, chal-

AM is a material joining process from a three-dimensional (3D) CAD model data to build an object, in typically layer by layer [32, 35]. AM has been known by names

lenges and suggested findings were discussed at the end of this work.

aerospace engines [25].

*DOI: http://dx.doi.org/10.5772/intechopen.85538*

Beta titanium (β-Ti) alloys is reported to have been used to fabricate landing gears in Boeing aircraft from the Ti-5Al-5Mo-5V-3Cr because of better strengthtoughness mishmash in β-Ti alloys compared to α + β and α alloys [8]. Titanium intermetallic alloys have great potentials in aerospace, automotive and power plants especially titanium aluminides (TiAl) because of their excellent creep and lightweight in relation to nickel-based superalloys [9]. The most feasible TiAl alloys with engineering interest are those of 44–48 at.% Al content because of the eutectoid transformation reaction occurring during solidification and cooling process [10]. **Figure 1** displays the phase diagram of Ti-Al between 0 and 60 at. % aluminum. Titanium matrix composites (TMCs) reinforced with ceramics has increased due to improvement in heavy load-bearing, wear and friction performance in service due to material efficiency with lower cost of parts fabrication.

A possible replacement of Ni-based superalloys is gamma-titanium aluminide (γ-TiAl) considered in manufacturing aero-engine and automobile engine parts because of their high strength, high stiffness, light weight good oxidation and corrosion resistance [11–20]. The choice of γ-TiAl is hinged on the fact that its density is almost half of Ni-based superalloy and high temperature creep properties [21, 22] with application temperature up to 750°C [23]. These has made γ-TiAl to be favorably accepted in aerospace industry. However, aero engine component like turbocharger operate at temperatures between 700 and 950°C which presents a concern of oxidation reaction apart from its room temperature ductility [22]. γ-TiAl

**Figure 1.** *Ti-Al binary phase diagram.*

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based… DOI: http://dx.doi.org/10.5772/intechopen.85538*

of 48 at.% Al generally comprise of a γ-phase and α2-phase with L1o and DO19 structure respectively (major: γ-TiAl, minor: α2-Ti3Al) typically referred to as γ-TiAl [10, 24]. This γ-TiAl-based alloy are continuously been improved upon in the manufacturing nozzles, low pressure turbine blade (LPTB) and turbochargers in aerospace engines [25].

General Electric has applied the Ti48Al2Cr2Nb alloy called the GE4822 to manufacture the Boeing-787 Dreamliner's engine known as GEnx-1B that reduces both fuel consumption and CO2 emission by 15% [11, 21, 26]. Due to the GE4822 alloys high-temperature capability, there has been works on improving the ductile property of γ-TiAl which have been used for low-pressure turbine (LPT) blades [11, 16, 18, 27] and to expand the temperature range 800–850°C [11]. High Nb-containing TiAl known as TNM have been produced with higher yield strength, oxidation resistance and better creep than conventional TiAls [15, 19, 23, 26, 28, 29].

However, the extremely poor tensile ductility (<1% elongation) of TiAl-based alloys at room temperature, poor fracture toughness and high-temperature poor workability makes it difficult to fabricate and strongly limits their applications in the industry [10, 13, 15, 16, 18, 30]. This has made conventional processing techniques very problematic in manufacturing TiAl-based components. Hence, a lot of interest in improving the ambient temperature characteristics and oxidation resistance at elevated temperature, methods such as alloying and post-processing heat treatment has been suggested to help advance its properties.

Apart from the potentially improved geometrical complexity, additive manufacturing (AM) permits manufacturing of innovative materials with functionally graded capabilities during fabrication [14]. The applicability of TiAl alloys is becoming more progressive due to the growing knowledge of the connections concerning mechanical properties and microstructural evolution as well as modifications in processing operations [18]. However, even with AM technologies issues of the mass production quantities is still not making the technique cost-effective [31].

Currently, AM has gained acceptance for manufacturing customized products with complex geometrical freedom, more homogeneous microstructure and functionally enhanced parts gradually replacing traditional processes [14, 28, 32]. Due to this property, it is possible to manufacture components and finished parts which could not be implemented with conventional manufacturing technologies or only at great expense. AM routes is poised to produced γ-TiAl parts for aerospace applications.

Laser additive manufacturing (LAM) is a class of AM process that makes use of high-powered laser beam in melting and fabricating metal powders into threedimensional (3D) components from a predesigned computer-aided design (CAD) model. One of the highly desirable LAM techniques is laser engineered net shaping (LENS®) regarded for producing ceramics, composites and functionally graded materials (FGMs) which are difficult to produce [33, 34].

The objective of this work is to give an overview of LAM of TiAl alloys and composites while presenting a review of crucial matters, investigation tendencies, fabrication and progress achieve on γ-TiAl based materials for aerospace. A succinct overview of TiAl was first presented followed by AM of titanium alloys particularly those applied in aerospace industries. The paper subsequently highlights a comprehensive appraisal of latest studies on γ-TiAl laser processing and post-processing effects on microstructural evolution and mechanical properties. Prospects, challenges and suggested findings were discussed at the end of this work.

## **2. Additive manufacturing (AM)**

AM is a material joining process from a three-dimensional (3D) CAD model data to build an object, in typically layer by layer [32, 35]. AM has been known by names

high strength-to-weight ratio in order to give high thrust, improved fuel efficiency at minimal fuel consumption while increasing speed of flight. Aircraft engines are usually fabricated by titanium alloys, nickel-based super alloys, superior steels or ultrahigh-temperature ceramics. Moreover, an important engineering material for manufacturing of gas turbine and aircraft engine components are alloys of titanium

strength and most especially their low density [1]. Also, due to the biocompatibility of these alloys, they have been applied in biomedical industries as implants [2–4] and prosthetic beak [5]. The poor wear performance and low hardness of titanium alloys constrained their adoption in fabricating components to be subjected in contact forces of friction and wear [3, 6]. Likewise, titanium alloys have not been impressive for load-bearing components (LBC) in the aerospace industry because

Beta titanium (β-Ti) alloys is reported to have been used to fabricate landing gears in Boeing aircraft from the Ti-5Al-5Mo-5V-3Cr because of better strengthtoughness mishmash in β-Ti alloys compared to α + β and α alloys [8]. Titanium intermetallic alloys have great potentials in aerospace, automotive and power plants especially titanium aluminides (TiAl) because of their excellent creep and lightweight in relation to nickel-based superalloys [9]. The most feasible TiAl alloys with engineering interest are those of 44–48 at.% Al content because of the eutectoid transformation reaction occurring during solidification and cooling process [10]. **Figure 1** displays the phase diagram of Ti-Al between 0 and 60 at. % aluminum. Titanium matrix composites (TMCs) reinforced with ceramics has increased due to improvement in heavy load-bearing, wear and friction performance in service due

A possible replacement of Ni-based superalloys is gamma-titanium aluminide (γ-TiAl) considered in manufacturing aero-engine and automobile engine parts because of their high strength, high stiffness, light weight good oxidation and corrosion resistance [11–20]. The choice of γ-TiAl is hinged on the fact that its density is almost half of Ni-based superalloy and high temperature creep properties [21, 22] with application temperature up to 750°C [23]. These has made γ-TiAl to be favorably accepted in aerospace industry. However, aero engine component like turbocharger operate at temperatures between 700 and 950°C which presents a concern of oxidation reaction apart from its room temperature ductility [22]. γ-TiAl

(Ti) because of good properties like corrosion resistance, excellent specific

of uneven stress distribution on parts [7].

*Aerodynamics*

**Figure 1.**

**194**

*Ti-Al binary phase diagram.*

to material efficiency with lower cost of parts fabrication.

which includes freeform fabrication (FFF), additive layer manufacturing (ALM), rapid prototyping (RP) and 3D-printing (3DP). AM have been widely adopted in industries especially the aerospace and medical field with recent application in radio-frequency (RF) for microwave and millimeter wave devices [32]. The distinguishing feature of this technology is ability to manufacture objects through layer upon layer building [36] and consistent component functions requiring little or no additional process [37].

industry followed by the medical industry while its gradually been accepted in automotive industry. AM presents encouraging platform to produce highly effective Ti-alloy component with intricate geometry [43, 44]. Whereas, these alloys are continuously been studied, the problem encountered is due to their additional

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based…*

Laser-based AM, however, achieves the built parts defined in a CAD model by melting and solidifying powder on a layer by layer basis [45]. This method is known to have been adopted in aerospace to manufacture and create components of graded material using Ti-based alloys. The LAM technologies produce fully dense parts from wire or powder feedstock [46, 47]. It has the merit of cost and time saving in comparison to traditional methods of casting and forging. A pertinent problem encountered in LAM when processing titanium matrix composites form various literatures is the unevenness of particle distribution. Also, the appearance of non-

One of the titanium alloys that are ideal for aerospace applications is the β-Ti alloy because it has a combined property of high strength and lightweight [48]. Titanium alloys have proven to be extremely attractive and important materials in aerospace applications because of excellent combinations of outstanding corrosion and mechanical properties [39, 47, 49, 50]. Recently, there has been increased interests in the development of additively manufactured titanium (and their alloys) parts in industries. However, the widespread applications are mitigated by expensive processing involved compared to some material of similar function [39].

A lot of studies have shown that Ti-alloys produced by AM possess considerable better mechanical properties than the conventional materials. Also, recent development has led to increased acceptance of the technologies, contributing new poten-

Saboori et al. [31] presented a review of AM on titanium components by direct laser deposition (DLD) analyzing the significance prospects of DED process. The connection among titanium alloys microstructural characteristics and process parameters were outlined. It was understood that DED processed parts undergo complex thermal history severely induced due to process uncertainties and process parameters. Even with attempts in optimizing process parameters to curtail flaws, enhance mechanical properties and microstructure of the component, there still existed the challenge of striking a balance. However, titanium parts fabricated by DED still had increased strength and poor ductile properties. It was stated that this

tial concerning functional incorporation and lightweight components.

alloy suffer anisotropy in the tensile characteristics because components fabricated horizontally demonstrate increased ductile strength compared with

power in varying microhardness of LENS processed TiB-TMCs.

In the work of Hu et al. [3], titanium matrix composites (TMC) has been fabricated by LENS using a 3D quasi continuous network (3DQCN) and TiB as reinforcement. The author examined the influence of energy input and reinforcement on parts quality and wear resistance. Superior wear performance was recorded as a result of TiB addition as a reinforcement. In a related work by Hu et al. [6], the author examined the influence of laser power and TiB reinforcement on mechanical properties. It was shown that laser power greatly affects the resulting microstructures but the strengthening of TiB increases the ultimate compressive strength (UCS) and microhardness of TiB-TMCs. **Table 2** shows influence of laser

Also, the mechanical properties and defects (porosity) of TiB-TMCs parts fabricated using an innovative ultrasonic vibration-assisted (UV-A) LENS have been

processing requirements.

those build vertically.

**197**

melted particles leading to reduced plasticity.

*DOI: http://dx.doi.org/10.5772/intechopen.85538*

**2.1 Additive manufacturing of titanium alloys**

The two key classes of AM technologies are direct energy deposition (DED) and powder bed fusion (PBF) as depicted in **Table 1**. The DED methods offers prospects in engineering applications for producing functional parts with intricate geometries from metallic powders [31]. The powder particles used are preferably spherical with the DED being more sensitive in size distribution and wires are adopted as precursor for certain DED processes for higher production rate [38]. The process melts the material feedstock (powder or wire) using a high-powered laser beam. The most commonly used lasers are CO2 and ND: YAG which has been used for fabricating complex and customized parts, prototyping of metallic parts and repairing/cladding of components [31]. This method is ideal to directly make components with limited tooling but the produced parts exhibits relatively low fracture toughness and prone to defects like cracks and pores due to fast heating and cooling rates involved [39, 40].

In the PBF techniques, a heating source (laser or electron beam) scans metallic powders on a preplaced build platform to melt the powders in a predefined path. This is controlled based on CAD model to build the object in a layer by layer tool path. It has the benefits of reduced lead time and material waste [41] and control of melt pool dynamics and stability [42].

There have been remarkable improvements in AM primarily by the Ti alloys production for aerospace components. Though, PBF is competent to make near-net shaped objects and DED also can be applied to refurbish/repair parts and modify features apart from fabricating 3D objects. The high-temperature gradient due to focused instant heating and cooling is the main difficulty encountered by these techniques.

The majority of investigations on AM materials demonstrates that their mechanical properties of better than the traditionally manufactured titanium alloys. The principal application of additive manufactured Ti-alloy is the aerospace


**Table 1.**

*The major classes of additive manufacturing (AM).*

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based… DOI: http://dx.doi.org/10.5772/intechopen.85538*

industry followed by the medical industry while its gradually been accepted in automotive industry. AM presents encouraging platform to produce highly effective Ti-alloy component with intricate geometry [43, 44]. Whereas, these alloys are continuously been studied, the problem encountered is due to their additional processing requirements.

Laser-based AM, however, achieves the built parts defined in a CAD model by melting and solidifying powder on a layer by layer basis [45]. This method is known to have been adopted in aerospace to manufacture and create components of graded material using Ti-based alloys. The LAM technologies produce fully dense parts from wire or powder feedstock [46, 47]. It has the merit of cost and time saving in comparison to traditional methods of casting and forging. A pertinent problem encountered in LAM when processing titanium matrix composites form various literatures is the unevenness of particle distribution. Also, the appearance of nonmelted particles leading to reduced plasticity.

#### **2.1 Additive manufacturing of titanium alloys**

One of the titanium alloys that are ideal for aerospace applications is the β-Ti alloy because it has a combined property of high strength and lightweight [48]. Titanium alloys have proven to be extremely attractive and important materials in aerospace applications because of excellent combinations of outstanding corrosion and mechanical properties [39, 47, 49, 50]. Recently, there has been increased interests in the development of additively manufactured titanium (and their alloys) parts in industries. However, the widespread applications are mitigated by expensive processing involved compared to some material of similar function [39].

A lot of studies have shown that Ti-alloys produced by AM possess considerable better mechanical properties than the conventional materials. Also, recent development has led to increased acceptance of the technologies, contributing new potential concerning functional incorporation and lightweight components.

Saboori et al. [31] presented a review of AM on titanium components by direct laser deposition (DLD) analyzing the significance prospects of DED process. The connection among titanium alloys microstructural characteristics and process parameters were outlined. It was understood that DED processed parts undergo complex thermal history severely induced due to process uncertainties and process parameters. Even with attempts in optimizing process parameters to curtail flaws, enhance mechanical properties and microstructure of the component, there still existed the challenge of striking a balance. However, titanium parts fabricated by DED still had increased strength and poor ductile properties. It was stated that this alloy suffer anisotropy in the tensile characteristics because components fabricated horizontally demonstrate increased ductile strength compared with those build vertically.

In the work of Hu et al. [3], titanium matrix composites (TMC) has been fabricated by LENS using a 3D quasi continuous network (3DQCN) and TiB as reinforcement. The author examined the influence of energy input and reinforcement on parts quality and wear resistance. Superior wear performance was recorded as a result of TiB addition as a reinforcement. In a related work by Hu et al. [6], the author examined the influence of laser power and TiB reinforcement on mechanical properties. It was shown that laser power greatly affects the resulting microstructures but the strengthening of TiB increases the ultimate compressive strength (UCS) and microhardness of TiB-TMCs. **Table 2** shows influence of laser power in varying microhardness of LENS processed TiB-TMCs.

Also, the mechanical properties and defects (porosity) of TiB-TMCs parts fabricated using an innovative ultrasonic vibration-assisted (UV-A) LENS have been

which includes freeform fabrication (FFF), additive layer manufacturing (ALM), rapid prototyping (RP) and 3D-printing (3DP). AM have been widely adopted in industries especially the aerospace and medical field with recent application in radio-frequency (RF) for microwave and millimeter wave devices [32]. The distinguishing feature of this technology is ability to manufacture objects through layer upon layer building [36] and consistent component functions requiring little

The two key classes of AM technologies are direct energy deposition (DED) and powder bed fusion (PBF) as depicted in **Table 1**. The DED methods offers prospects in engineering applications for producing functional parts with intricate geometries from metallic powders [31]. The powder particles used are preferably spherical with the DED being more sensitive in size distribution and wires are adopted as precursor for certain DED processes for higher production rate [38]. The process melts the material feedstock (powder or wire) using a high-powered laser beam. The most commonly used lasers are CO2 and ND: YAG which has been used for fabricating complex and customized parts, prototyping of metallic parts and repairing/cladding of components [31]. This method is ideal to directly make components with limited tooling but the produced parts exhibits relatively low fracture toughness and prone to defects like cracks and pores due to fast heating and

In the PBF techniques, a heating source (laser or electron beam) scans metallic powders on a preplaced build platform to melt the powders in a predefined path. This is controlled based on CAD model to build the object in a layer by layer tool path. It has the benefits of reduced lead time and material waste [41] and control of

There have been remarkable improvements in AM primarily by the Ti alloys production for aerospace components. Though, PBF is competent to make near-net shaped objects and DED also can be applied to refurbish/repair parts and modify features apart from fabricating 3D objects. The high-temperature gradient due to focused instant heating and cooling is the main difficulty encountered by these

The majority of investigations on AM materials demonstrates that their mechanical properties of better than the traditionally manufactured titanium alloys.

The principal application of additive manufactured Ti-alloy is the aerospace

**Classes Technology Source of energy Material used**

Electron beam, laser beam

Metal, ceramics and

polymers

Laser beam Metals (powder and wire)

or no additional process [37].

*Aerodynamics*

cooling rates involved [39, 40].

techniques.

Directed energy deposition (DED)

**Table 1.**

**196**

melt pool dynamics and stability [42].

Powder bed fusion (PBF) Electron beam melting

(EBM)

(SLM)

(DMLS)

(SLS)

(EBW)

*The major classes of additive manufacturing (AM).*

Selective laser melting

Direct metal laser sintering

Selective laser sintering

Laser engineered net shaping (LENS)

Electronic beam welding

Laser cladding


#### **Table 2.**

*Microhardness comparison of TiB-TMCs.*

investigated by Ning, Hu and Cong [51]. The procedure adopted exhibited remarkable influences on porosity, pore size, TiB whisker size and distribution, QCN microstructural grain size and microhardness. Consequently, fine microstructures were obtained due to refinements of both TiB whiskers and QCN microstructural grains UV-A LENS providing larger area of grain boundaries to hinder the dislocation motion, thus improving the microhardness of fabricated parts.

through LENS technique. A specific single β-phase is identified in 20 wt% V while the dual-phase microstructure in Ti-12 wt% Mo system revealed α-phase in β-grain morphology. This was accredited to the build directions that had different thermal

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based…*

In the work of Li et al. [47], LAM was used to fabricate Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si alloy in order to examine tensile strength and microhardness of the alloy. Mixed columnar β-grains with no equiaxed microstructure was observed

Song et al. [5] reported the titanium alloy to fabricate a prosthetic beak as shown in (**Figure 3**) for a bird (*Grus japonensis*) using SLM. A model was first developed for the titanium alloy customized beak and was successfully completed to save the

for as-deposited alloy. The addition of Zr, Mo and Si causes increase in microhardness value because of hardening effect of their solid solution. Also

noticed, was the rise in ductility in comparison to Ti-6Al-4V.

*SLM fabricated prosthesis beaks: (a) as-fabricated (b) polished and surface treated [5].*

*SEM images of (A) CPTi-BN [45] (B) CPTi-Zr-BN [45] compositions.*

cycles at various portion of the builds.

*DOI: http://dx.doi.org/10.5772/intechopen.85538*

endangered bird.

**Figure 3.**

**199**

**Figure 2.**

A research was conducted by Grove et al. [50] to investigate and compare the surface integrity and machinability of Ti-5553 alloy with composition Ti-5Al-5V-5Mo-3Cr produced by casting, SLM and SLM + heat treatment (in-situ). Higher tool wear was noticed in the in-situ heat treated alloy while the tool wear for the other two does not seem to differ. Therefore, it proves titanium alloys' machinability is extremely affected further processing methods.

According to Uhlmann et al. [52], the aviation industry requires a drastic reduction in NOx and CO2 emission in the coming years ahead. The authors'study was focused on highly effective and efficient titanium alloys with optimizing process parameters for structures manufactured by the SLM machine. The post-processing of TiAl6V4 parts fabricated by SLM display vast possibility of enhancing surface quality. Examination of computed tomography and microstructure confirms that porosity of titanium alloy parts can be minimized through HIP-process.

Silica (SiCO2) coatings have been created on commercially-pure titanium (Cp-Ti) by Heer and Bandyopadhyay [53] using LENS with subsequent stress relieve heat treatments and post-deposition laser passes. Ti5Si3 phase was formed leading to high hardness of 1500 HV in the coatings and wear rate was mostly reduced in comparison to Cp-Ti irrespective of heat treatment as well as rise in laser pass commonly reduce wear rates. The microstructures revealed dendrite shaped and morphology of columnar deposit around primarily matrix of α-titanium.

A process of reactive deposition AM was adopted by Traxel and Bandyopadhyay [45] for maintaining Ti-Zr-BN composite parts using commercially pure titanium (Cp-Ti) with addition of Zr and BN. This was aimed at improving elevated temperature and wear resistance abilities if TMC using LENS. The as-fabricated BN-containing components shows TiB2, TiN and TiB as reinforcement with SEM image of CpTi-BN and CpTi-Zr-BN presented in **Figure 2** below. Zr-addition displays a combination of composites of composites and alloys leading to high hardness and ultimate compressive strength (UCS) with enhanced wear resistance. This method is expected to be used in creating novel coatings and structures from vast powder feedstocks to develop the bulk and surface characteristics of titanium related metals.

Effects of thermal history and build direction were studied by Mantri and Banerjee [48] on β-Ti alloys containing Mo-12 wt% and V-20 wt%, produced

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based… DOI: http://dx.doi.org/10.5772/intechopen.85538*

**Figure 2.** *SEM images of (A) CPTi-BN [45] (B) CPTi-Zr-BN [45] compositions.*

through LENS technique. A specific single β-phase is identified in 20 wt% V while the dual-phase microstructure in Ti-12 wt% Mo system revealed α-phase in β-grain morphology. This was accredited to the build directions that had different thermal cycles at various portion of the builds.

In the work of Li et al. [47], LAM was used to fabricate Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si alloy in order to examine tensile strength and microhardness of the alloy. Mixed columnar β-grains with no equiaxed microstructure was observed for as-deposited alloy. The addition of Zr, Mo and Si causes increase in microhardness value because of hardening effect of their solid solution. Also noticed, was the rise in ductility in comparison to Ti-6Al-4V.

Song et al. [5] reported the titanium alloy to fabricate a prosthetic beak as shown in (**Figure 3**) for a bird (*Grus japonensis*) using SLM. A model was first developed for the titanium alloy customized beak and was successfully completed to save the endangered bird.

investigated by Ning, Hu and Cong [51]. The procedure adopted exhibited remarkable influences on porosity, pore size, TiB whisker size and distribution, QCN microstructural grain size and microhardness. Consequently, fine microstructures were obtained due to refinements of both TiB whiskers and QCN microstructural grains UV-A LENS providing larger area of grain boundaries to hinder the dislocation motion, thus improving the microhardness of fabricated parts.

**Materials Laser power Microhardness (HV1.0) Processing** Cp-Ti 200 W 345.5 5.4 [3] LENS Cp-Ti 125 W 304 10 [6] LENS TiB-TMCs 200 W 392.6 8.9 [3] LENS TiB-TMCs 125 W 339 9 [6] LENS TiB-TMCs 200 W 393 9 [6] LENS TiB-TMCs 200 W 405–429 [52] UV-A LENS TiB-TMCs 300 W 428–488 [52] UV-A LENS

A research was conducted by Grove et al. [50] to investigate and compare the surface integrity and machinability of Ti-5553 alloy with composition Ti-5Al-5V-5Mo-3Cr produced by casting, SLM and SLM + heat treatment (in-situ). Higher tool wear was noticed in the in-situ heat treated alloy while the tool wear for the other two does not seem to differ. Therefore, it proves titanium alloys' machinability is

According to Uhlmann et al. [52], the aviation industry requires a drastic reduction in NOx and CO2 emission in the coming years ahead. The authors'study was focused on highly effective and efficient titanium alloys with optimizing process parameters for structures manufactured by the SLM machine. The post-processing of TiAl6V4 parts fabricated by SLM display vast possibility of enhancing surface quality. Examination of computed tomography and microstructure confirms that

Silica (SiCO2) coatings have been created on commercially-pure titanium (Cp-Ti) by Heer and Bandyopadhyay [53] using LENS with subsequent stress relieve heat treatments and post-deposition laser passes. Ti5Si3 phase was formed leading to high hardness of 1500 HV in the coatings and wear rate was mostly reduced in comparison to Cp-Ti irrespective of heat treatment as well as rise in laser pass commonly reduce wear rates. The microstructures revealed dendrite shaped and

A process of reactive deposition AM was adopted by Traxel and Bandyopadhyay [45] for maintaining Ti-Zr-BN composite parts using commercially pure titanium (Cp-Ti) with addition of Zr and BN. This was aimed at improving elevated temperature and wear resistance abilities if TMC using LENS. The as-fabricated BN-containing components shows TiB2, TiN and TiB as reinforcement with SEM image of CpTi-BN and CpTi-Zr-BN presented in **Figure 2** below. Zr-addition displays a combination of composites of composites and alloys leading to high hardness and ultimate compressive strength (UCS) with enhanced wear resistance. This method is expected to be used in creating novel coatings and structures from vast powder feedstocks to develop the bulk and surface characteristics of titanium

Effects of thermal history and build direction were studied by Mantri and Banerjee [48] on β-Ti alloys containing Mo-12 wt% and V-20 wt%, produced

porosity of titanium alloy parts can be minimized through HIP-process.

morphology of columnar deposit around primarily matrix of α-titanium.

extremely affected further processing methods.

related metals.

**198**

**Table 2.**

*Aerodynamics*

*Microhardness comparison of TiB-TMCs.*

A comparative study of SLM and electron beam melting (EBM) carried out by Zhao et al. [54] to fabricate Ti-6Al-4V parts. Both components largely contained α + β and α<sup>0</sup> phase, respectively. SLM samples had higher tensile strength but lower ductility than EBM fabricated parts. Even though porosity was observed in both cases it was much higher in SLM parts. While generally, samples fabricated in the vertical direction had increased ultimate tensile strength, yield strength, and improve ductility than those in the horizontal orientation.

Direct metal deposition (DMD) has been used by Pouzet et al. [55] to build samples with varying volume fractions of TiB + TiC. The Coaxial deposition process fabricated TMC from powder mixture of T-6Al-4V + B4C. Pure and consistent Ti-6Al-4V-TiB microstructure was noticed and boron isolation during solidification of β-Ti resulted in grain refinements. At low B4C, TiC was not observed which was ascribed to high solubility of C in α-Ti at high solidification rate leading to decreased tensile strength at elevated and room temperature.

#### **2.2 Laser additive manufacturing (LAM) of titanium aluminides**

TiAl are known to be favorable for high-temperature component because of their high strength-to-weight ratio, high melting point, attractive creep and superior modulus of elasticity [56]. Recently, TiAl-based alloys have been effectively applied in aircraft engine productions with increase in demand for these alloys expected in the near future [57].

Microstructure and phase composition are immensely determining the properties of intermetallic TiAl-based alloys. Elements like Mo, V, Zr, Mn, Nb, Cr, Ni and Fe are known to be employed in developing enhanced mechanical properties for TiAl [58, 59]. The site effects for most of the elements remains unchanged with the different alloy compositions. However, Cr, Mn and V site substitution vary subject to Ti:Al ratio [59]. It is commonly accepted that a microstructure of equiaxed fine grains are desirable to enhance strength and ductility whereas coarse microstructure of fully lamellar is better for high creep.

The lack of ductility of TiAl at room temperature makes it problematic to machine and fabricate components by traditional methods. AM is very promising to incorporating design freedoms and processing when building components [60]. LENS and selective laser melting/sintering (SLM/SLS) are primarily known as LAM techniques. Various AM technologies are called by their trade names from the manufacturers or company of establishments [61]. A laser engineered net shaping (LENS) Optomec 850R machine for AM system is shown in **Figure 4**. This technique is suitable for manufacturing and realization of complex geometries with reduced lead time and material loss [62]. The process uses a focused laser beam for melting and fusion producing 3D parts from feedstock powder. Apart from building components (**Figure 5**), it refurbishes components through a process called laser cladding. This is believed to be the state-of-the-art technique for aero engine parts repairing [63].

levels due to highly efficient fuel usage [63]. Advances in recent development techniques has led to collaborations among manufacturers. This is made possible to fabricate turbine blades using electron beam melting (EBM) from pre-alloyed

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based…*

DED was adopted by Hoosain et al. [10] to create clads of γ-TiAl using in-situ elemental Ti and Al powder. The purpose of the study was to optimize formation of γ-phase during laser processing through mass flow rates. Depending on flow rate of Al and heat treatment both duplex and lamellar phases are observed. Also, Al content largely determines the microhardness and twinning existence. In another work, Hoosain et al. [56] investigated the consequences of Al flow rate on microstructure of in-situ alloy composition. The γ-TiAl was compared with Ti4822, a duplex phase microstructure was observed as Al feed rate increase. Fine lamellar grains were not generated for heat treatment temperature at 1200°C because it was below the temperature of α-transus. **Figure 6** presents the microstructure of com-

In the feasibility study carried out by Dilip et al. [65], Ti-6Al-4V and Al powder was employed to samples of TiAl using binder jetting AM and reactive sintering.

Ti4822 powder, presently employed in GEnx engines [60, 64].

mercial GE alloy Ti-48Al-2Cr-2Nb alloys.

**Figure 5.**

**201**

**Figure 4.**

*LENS Optomec 850R additive manufacturing system.*

*DOI: http://dx.doi.org/10.5772/intechopen.85538*

*LENS Fabricated Object.*

For aerospace components materials, when compared with conventionally applied materials like Ni-based superalloys, TiAl is far harder and offers close to 50% weight savings. This results in decrease cost of turbine operations and emission levels due to highly efficient fuel usage [63]. Advances in recent development techniques has led to collaborations among manufacturers. This is made possible to fabricate turbine blades using electron beam melting (EBM) from pre-alloyed Ti4822 powder, presently employed in GEnx engines [60, 64].

For aerospace components materials, when compared with conventionally applied materials like Ni-based superalloys, TiAl far harder and offers close to 50% weight savings. This results in decrease cost of turbine operations and emission

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based… DOI: http://dx.doi.org/10.5772/intechopen.85538*

**Figure 4.** *LENS Optomec 850R additive manufacturing system.*

**Figure 5.** *LENS Fabricated Object.*

A comparative study of SLM and electron beam melting (EBM) carried out by Zhao et al. [54] to fabricate Ti-6Al-4V parts. Both components largely contained α + β and α<sup>0</sup> phase, respectively. SLM samples had higher tensile strength but lower ductility than EBM fabricated parts. Even though porosity was observed in both cases it was much higher in SLM parts. While generally, samples fabricated in the vertical direction had increased ultimate tensile strength, yield strength, and

Direct metal deposition (DMD) has been used by Pouzet et al. [55] to build samples with varying volume fractions of TiB + TiC. The Coaxial deposition process fabricated TMC from powder mixture of T-6Al-4V + B4C. Pure and consistent Ti-6Al-4V-TiB microstructure was noticed and boron isolation during solidification of β-Ti resulted in grain refinements. At low B4C, TiC was not observed which was ascribed to high solubility of C in α-Ti at high solidification rate leading to decreased

TiAl are known to be favorable for high-temperature component because of their high strength-to-weight ratio, high melting point, attractive creep and superior modulus of elasticity [56]. Recently, TiAl-based alloys have been effectively applied in aircraft engine productions with increase in demand for these alloys

Microstructure and phase composition are immensely determining the properties of intermetallic TiAl-based alloys. Elements like Mo, V, Zr, Mn, Nb, Cr, Ni and Fe are known to be employed in developing enhanced mechanical properties for TiAl [58, 59]. The site effects for most of the elements remains unchanged with the different alloy compositions. However, Cr, Mn and V site substitution vary subject to Ti:Al ratio [59]. It is commonly accepted that a microstructure of equiaxed fine grains are desirable to enhance strength and ductility whereas coarse microstructure

The lack of ductility of TiAl at room temperature makes it problematic to machine and fabricate components by traditional methods. AM is very promising to incorporating design freedoms and processing when building components [60]. LENS and selective laser melting/sintering (SLM/SLS) are primarily known as LAM techniques. Various AM technologies are called by their trade names from the manufacturers or company of establishments [61]. A laser engineered net shaping (LENS) Optomec 850R machine for AM system is shown in **Figure 4**. This technique is suitable for manufacturing and realization of complex geometries with reduced lead time and material loss [62]. The process uses a focused laser beam for melting and fusion producing 3D parts from feedstock powder. Apart from building components (**Figure 5**), it refurbishes components through a process called laser cladding. This is believed to be the state-of-the-art technique for aero

For aerospace components materials, when compared with conventionally applied materials like Ni-based superalloys, TiAl is far harder and offers close to 50% weight savings. This results in decrease cost of turbine operations and emission levels due to highly efficient fuel usage [63]. Advances in recent development techniques has led to collaborations among manufacturers. This is made possible to fabricate turbine blades using electron beam melting (EBM) from pre-alloyed

For aerospace components materials, when compared with conventionally applied materials like Ni-based superalloys, TiAl far harder and offers close to 50% weight savings. This results in decrease cost of turbine operations and emission

Ti4822 powder, presently employed in GEnx engines [60, 64].

improve ductility than those in the horizontal orientation.

tensile strength at elevated and room temperature.

expected in the near future [57].

*Aerodynamics*

of fully lamellar is better for high creep.

engine parts repairing [63].

**200**

**2.2 Laser additive manufacturing (LAM) of titanium aluminides**

levels due to highly efficient fuel usage [63]. Advances in recent development techniques has led to collaborations among manufacturers. This is made possible to fabricate turbine blades using electron beam melting (EBM) from pre-alloyed Ti4822 powder, presently employed in GEnx engines [60, 64].

DED was adopted by Hoosain et al. [10] to create clads of γ-TiAl using in-situ elemental Ti and Al powder. The purpose of the study was to optimize formation of γ-phase during laser processing through mass flow rates. Depending on flow rate of Al and heat treatment both duplex and lamellar phases are observed. Also, Al content largely determines the microhardness and twinning existence. In another work, Hoosain et al. [56] investigated the consequences of Al flow rate on microstructure of in-situ alloy composition. The γ-TiAl was compared with Ti4822, a duplex phase microstructure was observed as Al feed rate increase. Fine lamellar grains were not generated for heat treatment temperature at 1200°C because it was below the temperature of α-transus. **Figure 6** presents the microstructure of commercial GE alloy Ti-48Al-2Cr-2Nb alloys.

In the feasibility study carried out by Dilip et al. [65], Ti-6Al-4V and Al powder was employed to samples of TiAl using binder jetting AM and reactive sintering.

## *Aerodynamics*

Initially, Al3Ti formation was obtained in the liquid phase due to Ti64 and Al reaction. Afterwards, TiAl was formed has diffusion of Al continues with sintering time. Other intermetallic together with TiAl phases were obtained in the final microstructure.

process, three phase transformation of α<sup>2</sup> + γ ! B2, α<sup>2</sup> ! B2, α<sup>2</sup> ! γ was noticed. An increase in hardness was ascribed to rapidly raising quantity of lamellar colonies

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based…*

The structure of TiAl alloys was examined by Li et al. [68] for detailed characterization of SLM processed Ti-45Al-2Cr-5Nb alloy. Anisotropy of microstructure were obtained has the sides contained columnar grains while the top showed equiaxed microstructure. The processed sample was overshadowed with high angle grain boundaries (HAGBs) which is favored by the energy density. Also, evenly dispersed minute quantities of B2 and γ phases (nano meters range) were found in α<sup>2</sup> matrix γ and B2 phase reduces with raising energy density whereas α<sup>2</sup> content

Sharman, Hughes and Ridgway [61] stated that previous works on LAM had concluded that it was merely impossible to manufacture component of TiAl that are crack free without additional heating to influence the solidification process. It was demonstrated that by defocusing the laser across build surface heats the particles ahead of entering melting zone. Hence, decrease rate of cooling lower than the

Oxide dispersion strengthen (ODS) has been used by Kenel et al. [14] to fabricate Ti-45Al-3Nb- < 0.2Y2O3 at.% and studied the microstructure. The traditional microstructure of α<sup>2</sup> + γ and near-lamellar were observed. The ODS-TiAl alloy displays greater hardness than ones without the reinforcement. β-solidifying TiAl was studied by Gussone et al. [69] fabricated by SLM of γ-TiAl pre-alloyed powder. Under cooling of β occurred due to tremendous Al loss leading to β/B2 microstructure. During SLM and hot isostatic pressing (HIP), the raise in content of oxygen

Seifi et al. [70] conducted and experiment to evaluate the mechanical properties and microstructure of EBM γ-TiAl with HIP. The two conditions presented microstructure of heterogenous interchanging γ-grains of coarse and fine bands. It is worthy to note that the EBM samples revealed microcracks at secluded sections all over the builds. The consequence of beam current on microstructure and grain boundary orientation had been studied by Yue et al. [71] for Ti-47Al-2Cr-2Nb manufactured by selective electron beam melting (SEBM). Increases beam current resulted in resulted in microstructural transformation to near-γ structure to fine duplex phase and B2-phase volume fraction steadily rises. Also, HAGB increases progressively with beam current while the low angle grain boundary (LAGB)

In establishing a relationship among scan speed, microstructure and mechanical properties, Li et al. [18] fabricated Ti-45Al-2Cr-2Nb parts using SLM. The grain size reduces with laser scan while crystallographic topography basically remains unchanged. The phases of B2 and γ rises with increased scan speed whereas α2-phase is lowered. It was also reported that nanohardness and compressive

Chen, Yue and Wang [72] studied SEBM sample using various scan speed to produce Ti-47Al-2Cr-2Nb alloys. Microstructural changed occurred to duplex from near-γ structure as the scan speed rises. However, both α<sup>2</sup> and B2 phases are homogenously dispersed in the matrix of γ. Ultimate compressive strength (UTS) of

Statistical examination was used by Shi et al. [73] to optimize process parameter of SLM Ti-47Al-2Cr-2Nb on Ti-6Al-4V substrate. It was understood that unsuitable amalgamation of process parameters would lead to instability of melt pool, cracks balling and other defects. To optimize the process, Al loss need to be taken into account. The ideal process parameter obtained was able to build TiAl components

strength rises with improved scan speed for the SLM TiAl alloy.

SEBM-produced TiAl alloy generally increased with the scanning speed.

α2/γ has the built height increases.

*DOI: http://dx.doi.org/10.5772/intechopen.85538*

critical level that permits crack formation.

make the sample less ductile.

with 97.34–98.95% densities.

increases.

reduces.

**203**

Todai et al. [41] presented a study to manipulate Ti4822 alloy microstructure fabricated through EBM process. Duplex-like and γ-bands of layered microstructure were formed by recurring heat treatment of melt pool area. The angle of building substantially makes the tensile elongation and yield strength (YS) to vary. The XRD patterns of the EBM built Ti-48Al-2Cr-2Nb alloy in different directions are displayed in **Figure 7**. The anisotropy of YS reduces as temperature rises. The heat treatment at 700°C gave the highest YS which show decrease in value as temperature rises. EBM was also adopted by Murr et al. [66] in fabricating TiAl from precursor powders to investigate to hardness and microstructure produced. Microstructure of α2-Ti3Al was noticed for powder precursor whereas lamellar colony at γ/α<sup>2</sup> with equiaxed γ-TiAl was obtained for EBM samples. It was reported that the EBM-fabricated TiAl had microhardness of 4.1GPa which makes the YS far exceed that of EBM-fabricated Ti64.

Selective electron beam melting (SEBM) was adopted by Chen et al. [67], to investigate the microstructural variations of TiAl alloy samples and their impact on microhardness. A near lamellar structure was observed TiAl alloys. During the

#### **Figure 6.**

*Microstructure of the commercial GE alloy Ti-48Al-2Cr-2Nb (a) showing the lamellar type microstructure [56] and heat treated of at (b) 1200°C [10] and (c) 1430°C [10].*

**Figure 7.** *XRD pattern of Ti-48Al-2Cr-2Nb alloy specimens fabricated by EBM at 0°, 45° and 90° [41].*

*Laser Based Additive Manufacturing Technology for Fabrication of Titanium Aluminide-Based… DOI: http://dx.doi.org/10.5772/intechopen.85538*

process, three phase transformation of α<sup>2</sup> + γ ! B2, α<sup>2</sup> ! B2, α<sup>2</sup> ! γ was noticed. An increase in hardness was ascribed to rapidly raising quantity of lamellar colonies α2/γ has the built height increases.

The structure of TiAl alloys was examined by Li et al. [68] for detailed characterization of SLM processed Ti-45Al-2Cr-5Nb alloy. Anisotropy of microstructure were obtained has the sides contained columnar grains while the top showed equiaxed microstructure. The processed sample was overshadowed with high angle grain boundaries (HAGBs) which is favored by the energy density. Also, evenly dispersed minute quantities of B2 and γ phases (nano meters range) were found in α<sup>2</sup> matrix γ and B2 phase reduces with raising energy density whereas α<sup>2</sup> content increases.

Sharman, Hughes and Ridgway [61] stated that previous works on LAM had concluded that it was merely impossible to manufacture component of TiAl that are crack free without additional heating to influence the solidification process. It was demonstrated that by defocusing the laser across build surface heats the particles ahead of entering melting zone. Hence, decrease rate of cooling lower than the critical level that permits crack formation.

Oxide dispersion strengthen (ODS) has been used by Kenel et al. [14] to fabricate Ti-45Al-3Nb- < 0.2Y2O3 at.% and studied the microstructure. The traditional microstructure of α<sup>2</sup> + γ and near-lamellar were observed. The ODS-TiAl alloy displays greater hardness than ones without the reinforcement. β-solidifying TiAl was studied by Gussone et al. [69] fabricated by SLM of γ-TiAl pre-alloyed powder. Under cooling of β occurred due to tremendous Al loss leading to β/B2 microstructure. During SLM and hot isostatic pressing (HIP), the raise in content of oxygen make the sample less ductile.

Seifi et al. [70] conducted and experiment to evaluate the mechanical properties and microstructure of EBM γ-TiAl with HIP. The two conditions presented microstructure of heterogenous interchanging γ-grains of coarse and fine bands. It is worthy to note that the EBM samples revealed microcracks at secluded sections all over the builds. The consequence of beam current on microstructure and grain boundary orientation had been studied by Yue et al. [71] for Ti-47Al-2Cr-2Nb manufactured by selective electron beam melting (SEBM). Increases beam current resulted in resulted in microstructural transformation to near-γ structure to fine duplex phase and B2-phase volume fraction steadily rises. Also, HAGB increases progressively with beam current while the low angle grain boundary (LAGB) reduces.

In establishing a relationship among scan speed, microstructure and mechanical properties, Li et al. [18] fabricated Ti-45Al-2Cr-2Nb parts using SLM. The grain size reduces with laser scan while crystallographic topography basically remains unchanged. The phases of B2 and γ rises with increased scan speed whereas α2-phase is lowered. It was also reported that nanohardness and compressive strength rises with improved scan speed for the SLM TiAl alloy.

Chen, Yue and Wang [72] studied SEBM sample using various scan speed to produce Ti-47Al-2Cr-2Nb alloys. Microstructural changed occurred to duplex from near-γ structure as the scan speed rises. However, both α<sup>2</sup> and B2 phases are homogenously dispersed in the matrix of γ. Ultimate compressive strength (UTS) of SEBM-produced TiAl alloy generally increased with the scanning speed.

Statistical examination was used by Shi et al. [73] to optimize process parameter of SLM Ti-47Al-2Cr-2Nb on Ti-6Al-4V substrate. It was understood that unsuitable amalgamation of process parameters would lead to instability of melt pool, cracks balling and other defects. To optimize the process, Al loss need to be taken into account. The ideal process parameter obtained was able to build TiAl components with 97.34–98.95% densities.

Initially, Al3Ti formation was obtained in the liquid phase due to Ti64 and Al reaction. Afterwards, TiAl was formed has diffusion of Al continues with sintering time. Other intermetallic together with TiAl phases were obtained in the final

patterns of the EBM built Ti-48Al-2Cr-2Nb alloy in different directions are displayed in **Figure 7**. The anisotropy of YS reduces as temperature rises. The heat treatment at 700°C gave the highest YS which show decrease in value as temperature rises. EBM was also adopted by Murr et al. [66] in fabricating TiAl from precursor powders to investigate to hardness and microstructure produced. Microstructure of α2-Ti3Al was noticed for powder precursor whereas lamellar colony at γ/α<sup>2</sup> with equiaxed γ-TiAl was obtained for EBM samples. It was reported that the EBM-fabricated TiAl had microhardness of 4.1GPa which makes the YS far exceed

Todai et al. [41] presented a study to manipulate Ti4822 alloy microstructure fabricated through EBM process. Duplex-like and γ-bands of layered microstructure were formed by recurring heat treatment of melt pool area. The angle of building substantially makes the tensile elongation and yield strength (YS) to vary. The XRD

Selective electron beam melting (SEBM) was adopted by Chen et al. [67], to investigate the microstructural variations of TiAl alloy samples and their impact on microhardness. A near lamellar structure was observed TiAl alloys. During the

*Microstructure of the commercial GE alloy Ti-48Al-2Cr-2Nb (a) showing the lamellar type microstructure*

*XRD pattern of Ti-48Al-2Cr-2Nb alloy specimens fabricated by EBM at 0°, 45° and 90° [41].*

*[56] and heat treated of at (b) 1200°C [10] and (c) 1430°C [10].*

microstructure.

*Aerodynamics*

that of EBM-fabricated Ti64.

**Figure 6.**

**Figure 7.**

**202**
