Study of arc ion plated Ta-W coating on a titanium alloy

In this paper, arc ion plating (AIP) was used to deposit Ta-W coating on a titanium alloy. The microstructure and the properties of the coating/substrate system were studied. The results show that a 32 μm continuous pure α-Ta (W) coating without cracks and pores was successfully deposited on a titanium alloy. The Ta-W coating consisted of fine polycrystalline α-Ta (W) with an average grain size of 45.6 nm. α-Ta (W) maintained coherence with β titanium on the interface, which helped to promote α-Ta formation during the deposition. The hardness of the as-deposited Ta-W coating was obviously improved to 14.4-15 GPa primarily due to small grain size strengthening. The adhesion strength of Ta-W coating on the substrate was sufficient with a critical load of 58.6 N obtained from scratch testing. After vacuum heat treatment at 550-1050 °C for 3 h, the coating/substrate system showed good thermal stability with no obvious changes in phase composition and microstructure. The Ta-W coating exhibited good thermal shock resistance and provided effective protection for the substrate during the cyclic oxidation and laser pulse heating in air. Element diffusion, the formation of reaction products, interface reactions and the failure mechanism of the coating during the cyclic oxidation and laser pulse heating in air were also discussed. This work is meaningful to the preparation of refractory Ta-W coating using AIP and its application to titanium alloys.