**5. Challenges and critical issues**

subject to Al-content and quantities of Nb and/or Mo. At room temperature the

The microstructural evolution and room temperature fracture toughness β-solidifying TiAl alloy studied by Chen et al. [30], for Ti-45Al-2Nb-1.5V-1Mo-0.3Y (at.%). Fine near-lamellar containing majorly of fine grains and combinations of γ + β phases with lamellar colony boundaries. The precipitation of fine β and γ grains is deemed an inherent toughness system due to α2/β and α2/γ boundaries creating

The influence of heat treatment was studied by Tebaldo and Faga [97], on hardness of Ti48Al2Nb2Cr manufactured through EBM technology. It was noticed that only minor different in density occurred due heat treatment and micro porosity. Near-γ with equiaxed lamellar was obtained for samples not heat treated and fully lamellar achieved for heat treated samples. It was concluded that the developed alloy would be appropriate for manufacturing components in aircraft engines. An incorporation of both HIP and heat treatment was developed by Chen et al. [13], to enhance mechanical properties of TiAl alloy. Corresponding increment in elongation and YS was noticed for both duplex and lamellar structures. Reduction in TiAl alloy mechanical properties was evident from the observed microcracks. However, the combined production method showed a microcrack free microstructure, thereby enhancing the properties. Illustration of the processing routes are shown in

Mechanical and microstructure governing techniques was investigated by Zhao et al. [98], for Ti-46Al-2Nb-2V-1Mo-Y (at%). The α + β + γ phase pre-treatment by annealing actually gave raise to the breakdown of lamellar α/γ structures. Fully-lamellar was attained with prolong annealing whereas for two-step process,

*The processing routes adopted by Chen et al. [13] (a) separately (b) combined processing.*

The consequence of heat treatments was studied by Li et al. [96], to evaluate grains features, transformation of phases and hardness of Ti-45Al-2Cr-5Nb (at.%) produced through SLM. The grains of heat-treated parts are overshadowed with HAGBs that rises as temperature of annealing increases. SLM-fabricated alloy has D019 structure of α<sup>2</sup> phase but the B2-phase is a bcc structure and γ-phase illustrate

γ-phase appears in three different morphologies.

limited displacement movement successfully.

a L1o (bcc) structure.

*Aerodynamics*

**Figure 11**.

**Figure 11.**

**208**

According to Bünck et al. [58], recent manufacturing processes for aerospace parts are expected to be well developed and cost-effectively competitive methods. LAM parts have high surface roughness and structural inhomogeneity and usually necessitate supplementary treatments to diminish irregular microstructure. Inadequate ambient temperature ductile property of TiAl alloys deters processing. Even during forging using isothermal process, dies are preserved at considerably high temperatures. Practical issue still to be stopped is the reactivity of melting crucible with TiAl, besides the matters of cost [25]. Novel methods are required that permit the modification of satisfactory amount of ductility though preserving the exceptional strength and creep characteristics that aforementioned research works has unlocked. The solution to unravel this difficulty rests in essential consideration of fundamental relationship between the properties and microstructure mechanisms. Grain morphology control is a challenging issue for LAM of large metallic components. Numerous practices have extensively considered the additional characteristics of TiAl-based aerospace parts, comprising the practice of surface modeling, application of coatings and heat-treatment.

Presently, LAM has the prospective to develop typical manufacture techniques, specifically in creating of small size of extremely complicated components [100]. Manufacturers have previously presented low-pressure turbine blades (LPTB) of TiAl alloy in aero engines and more interest is shown for the development of TiAl, demonstrating the distinctiveness of the alloy. This is with a view that engine efficiency would be substantially better-quality, indicating decreased fuel utilization, CO2 emission and noise. Consequently, increases stress is envisaged for TiAl-LPTBs and necessitates adjusting processing routes to produce functional materials.

LAM is suggested to have benefits for aircraft engine components because it can easily translate designs to 3D component, produce customized parts and functional designs with complex and intricate features [36]. It also has potential of manufacturing parts with no waste, lightweight and minimal lead time of manufacturing. Hence, it has the ability to be exceptional scalable and manufacture final product with little or no post-processing.

## **6. Summary and conclusions**

Based on the reviewed works, it can be generally deduced that LAM processing of titanium aluminide suffers several set-backs militating against its wider acceptance in aerospace application. Although, it has attractive features making it to be qualified as a candidate material for aerospace applications, the processing and post-processing problems still needs to be looked into. It is expected that combined processes of alloying and heat treatment (in-situ and ex-situ) could result in appreciable ductility while maintaining other mechanical properties. Consequently,

researchers would be able to develop a mechanism of fabricating TiAl with better room and elevated temperature properties.

**References**

corsci.2016.07.005

[1] Zhang M, Shen M, Xin L, Ding X, Zhu S, Wang F. High vacuum arc ion plating TiAl coatings for protecting titanium alloy against oxidation at medium high temperatures. Corrosion Science. 2016;**112**:36-43. DOI: 10.1016/j.

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

behavior of commercial purity Ti/Ti– 6Al–2Zr–1Mo–1V structurally graded material fabricated by laser additive manufacturing. Scripta Materialia. 2014;

[8] Santhosh R, Geetha M, Rao MN. Recent developments in heat treatment of beta titanium alloys for aerospace applications. Transactions of the Indian

[9] Tlotleng M, Lengopeng T, Seerane MN, Pityana SL. Effects of heattreatment on the microstructure of TiAl-Nb produced with laser metal deposition technique. In: Proceedings of the Materials Science & Technology, October 8–12, 2017. Pittsburgh, Pennsylvania USA: David L. Lawrence Convention Center; 2017. DOI: http://hd

[10] Hoosain S, Pityana S, Freemantle C, Tlotleng M. Heat treatment of in situ laser-fabricated titanium aluminide. Metals. 2018;**8**(9):655. DOI: 10.3390/

[11] Kartavykh AV, Asnis EA, Piskun NV, Statkevich II, Gorshenkov MV, Korotitskiy AV. A promising microstructure/deformability adjustment of β-stabilized γ-TiAl intermetallics. Materials Letters. 2016;

[12] Cheng J, Yu Y, Fu L, Li F, Qiao Z, Li J, et al. Effect of TiB2 on dry-sliding tribological properties of TiAl

intermetallics. Tribology International.

[13] Chen L, Zhu L, Guan Y, Zhang B, Li J. Tougher TiAl alloy via integration of

**162**:180-184. DOI: 10.1016/j.

2013;**62**:91-99. DOI: 10.1016/j.

hot isostatic pressing and heat treatment. Materials Science and

matlet.2015.09.139

triboint.2013.02.006

Institute of Metals. 2017;**70**(7): 1681-1688. DOI: 10.1007/s12666-016-

l.handle.net/10204/9874

met8090655

0985-6

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

**74**:80-83. DOI: 10.1016/j. scriptamat.2013.11.002

[2] Sallica-Leva E, Jardini AL, Fogagnolo JB. Microstructure and mechanical behavior of porous Ti–6Al–4V parts obtained by selective laser melting. Journal of the Mechanical Behavior of Biomedical Materials. 2013;**26**:98-108. DOI: 10.1016/j.jmbbm.2013.05.011

[3] Hu Y, Ning F, Wang H, Cong W, Zhao B. Laser engineered net shaping of

microstructural TiB reinforced titanium matrix bulk composites: Microstructure and wear performance. Optics & Laser Technology. 2018;**99**:174-183. DOI: 10.1016/j.optlastec.2017.08.032

[4] Mohammad A, Al-Ahmari AM, Balla VK, Das M, Datta S, Yadav D, et al. In

biocompatibility of electron beam melted γ-TiAl. Materials & Design. 2017;**133**:186-194. DOI: 10.1016/j.

[5] Song C, Wang A, Wu Z, Chen Z, Yang Y, Wang D. The design and manufacturing of a titanium alloy beak for Grus japonensis using additive manufacturing. Materials & Design. 2017;**117**:410-416. DOI: 10.1016/j.

[6] Hu Y, Zhao B, Ning F, Wang H, Cong W. In-situ ultrafine threedimensional quasi-continuous network microstructural TiB reinforced titanium matrix composites fabrication using laser engineered net shaping. Materials Letters. 2017;**195**:116-119. DOI: 10.1016/

quasi-continuous network

vitro wear, corrosion and

matdes.2017.07.065

matdes.2016.11.092

j.matlet.2017.02.112

**211**

[7] Liang YJ, Liu D, Wang HM. Microstructure and mechanical
