Microstructure and Tribological Properties of the Ti₃AlC₂ Coating on A Ti–46Al–2Cr–2Nb Alloy

Abstract

TiAl-based intermetallic alloys are of great interest as structural materials for aerospace and automotive industries because they possess lightweight, high oxidation resistance and excellent elevated temperature strength. [1] Recently, besides the improvement of the room-temperature ductility and strength by the control of microstructure and alloying, much attention has also been paid to investigate the tribological properties of the TiAl based alloy under various environments. [2][3][4][5][6] However, several studies show that titanium aluminides have high friction coefficient and poor wear resistance, which are the major disadvantages hindering their practical applications related to tribology. [7] In order to enhance the wear resistance of TiAl intermetallics, we have improved the dry sliding wear resistance of the TiAl alloy by adding hard TiB 2 at the little expense of the mechanical properties. [8] Apart from this method, surface treatment is an alternative and effective way because of its convenience. The main surface treatments include plasma carburization, [9] laser treatment, [10] gas nitridation, [11] heating technique, [12] microarc oxidation, [13] plasma pack aluminizing, [14] and thermal oxidation treatment. [15] In addition, hot-press sintering is a possible process route to fabricate a thick coating with metallurgical bond to the substrate. Again, this method can fabricate the substrate and coating simultaneously from their individual powders, which would be favorable to enhance the adhesion and reduce internal stress between the coating and substrate.There are numerous moving machine assemblies in aerospace which operate in vacuum. Friction and wear are of vital importance in determining the efficiency, durability, reliability, and robustness of tribological systems in the applications. TiAl-based alloy is promising for aerospace applications, but in our previous work, it was found that the TiAl alloy in vacuum exhibits high friction coefficient and moderate wear rate. To overcome the shortfall, we attempt to prepare a Ti 3 AlC 2 self-lubricating coating on the Ti-46Al-2Cr-2Nb alloy substrate. Ti 3 AlC 2 is a member of MAX phase with layer structure like traditional solid lubricants, graphite, and MoS 2 . [16] Very recently, our group firstly found that Ti 3 AlC 2 exhibits excellent self-lubricity under vacuum degree from 2.0 Â 10 4 to 5 Pa with the coefficient of friction (CoF) as low as 0.2 and nearly no wear. [17] Again, the constituents of the TiAl and Ti 3 AlC 2 are very close, which may be very helpful to reduce interface stress and obtain high cohesion between the substrate and coating if Ti 3 AlC 2 is coated on TiAl surfaces.Based on the advantages mentioned above, in this work, a Ti 3 AlC 2 material was selected as coating on a Ti-46Al-2Cr-2Nb alloy via hot-press sintering process. The microstructure and hardness of the Ti 3 AlC 2 coating on Ti-46Al-2Cr-2Nb alloy were examined, and tribological behavior of the coating was evaluated in low vacuum. Also, the tribological properties of the...