Abstract
TiAl-based intermetallic alloys have come to the fore as the preferred alloys for high-temperature applications. Conventional methods (casting, forging, sheet forming, extrusion, etc.) have been applied to produce TiAl intermetallic alloys. However, the inherent limitations of conventional methods do not permit the production of the TiAl alloys with intricate geometries. Additive manufacturing technologies such as electron beam melting (EBM) and laser powder bed fusion (LPBF), were used to produce TiAl alloys with complex geometries. EBM technology can produce crack-free TiAl components but lacks geometrical accuracy. LPBF technology has great geometrical precision that could be used to produce TiAl alloys with tailored complex geometries, but cannot produce crack-free TiAl components. To satisfy the current industrial requirement of producing crack-free TiAl alloys with tailored geometries, the paper proposes a new heating model for the LPBF manufacturing process. The model could maintain even temperature between the solidified and subsequent layers, reducing temperature gradients (residual stress), which could eliminate crack formation. The new conceptualized model also opens a window for in situ heat treatment of the built samples to obtain the desired TiAl (γ-phase) and Ti3Al (α2-phase) intermetallic phases for high-temperature operations. In situ heat treatment would also improve the homogeneity of the microstructure of LPBF manufactured samples.
Highlights
There has been ongoing research for more than a century [1,2] on manufacturing intermetallic alloys for industrial applications due to their unique high-temperature applications [2,3], it was the collaborative research launched by Oak Ridge National Laboratory (ORNL) in 1980 [2,4,5] that fast-tracked the discovery of various methods of producing intermetallic alloys for industrial applications
Of all the intermetallic alloys developed by the ORNL project, titanium aluminide (TiAl)- and nickel aluminide (NiAl)-based intermetallic alloys have already found industrial applications or are close to commercialization [2,6]
Further research on in situ monitoring could help determine the optimum process parameters and the preheating temperatures that could permit the manufacturing of crack-free TiAl alloy components of intricate geometries with the TiAl (γ-phase) and Ti3 Al (α2 -phase) intermetallic phases via laser powder bed fusion (LPBF)
Summary
There has been ongoing research for more than a century [1,2] on manufacturing intermetallic alloys for industrial applications due to their unique high-temperature applications [2,3], it was the collaborative research launched by Oak Ridge National Laboratory (ORNL) in 1980 [2,4,5] that fast-tracked the discovery of various methods of producing intermetallic alloys for industrial applications. The two phase TiAl-based alloy can maintain its ordered crystal lattice until its melting point, which makes it ideal for high-temperature applications. The fully lamellar and nearly fully lamellar microstructures consisting of TiAl (γphase) and a small volume fraction of Ti3 Al (α2 -phase) demonstrated high oxidation resistance, high fracture toughness, high creep, and crack propagation resistance, which make such TiAl alloy phases ideal for high-temperature applications in comparison to the duplex and gamma microstructures [38,39]. Since the performance of a material does not depend only on its mechanical properties and on its geometrical configurations [12,28,40], using the emerging AM manufacturing technology to produce the two-phase γ(TiAl) + α2 (Ti3 Al) Ti-(44-49)Al alloy with near-net shapes would certainly improve its technical and functional performance
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