Oxidation Behaviors of a Sputtered NiCrAlY Coating on the Surface of a High Temperature Titanium Alloy

The effect of a sputtered NiCrAlY coating on the oxidation behaviors of the Ti-1100 high temperature titanium alloy in air between 600°C∼800°C has been investigated. The experimental results show that the oxidation resistance of the Ti alloy is greatly improved by the formation of an Al₂O₃ protective film of uniform thickness and good adherence to the surface. The coating has good spallation resistance due to the plasticity of its micrograin structure which permits the release of thermal stress between the coating and the substrate. However, as the alloy is oxidized at 800°C, an interdiffusions of Ti and Ni elements across the coating/substrate interface occur. Thus, TiO₂ forms on the surface of the coating and in its pores, which has the effect of lowering the oxidation resistance of the Ti alloy.