Wear behaviours of PVD-TiN coating onTi-6Al-4V alloy processed by laser powder bed fusion or conventionally processed

Ti-6Al-4V alloy is the most preferred alloy used in laser powder bed fusion (LPBF) and physical vapour deposition (PVD) coating may often be needed. However, whether the wear performance of the coating on the high hardness LPBF Ti-6Al-4V substrate may perform differently to that on the conventionally processed (CP) and significantly lower hardness alloy substrate has not been clear. In this study, dry sliding wear tests have been conducted on PVD TiN-coated Ti-6Al-4V samples processed either by LPBF or by CP, using WC-Co as counter material. It has been found that local fracturing of coating after being thinned to 0.4–0.5μm in both coated LPBF and CP samples is similar. The major wear mechanism leading to a gradually rapid increase in wear rate of the coated samples will be demonstrated and explained through a wear process described as thickness reduction and local fracturing of the coating before the widening of the wear track. It will be shown that the local fracturing of coating was accompanied by the local deformation in CP substrate due to its low hardness. For the LBPF substrate, the deformation was not readily observed. That the higher amount of deformation underneath the coating for the case of CP substrate has affected little the overall wear rate will be illustrated.