How Al and Ta Diffusion Responses the Oxidation of NiCoCrAlYTa Coatings: Experiments

The development of air engines and gas turbines requires higher combustion and turbine temperatures for higher propulsion force or power generation. More durable and oxidation resistant MCrAlX coatings are then needed. In our series of studies, how Al and Ta diffusion responses the growth of surface oxides in NiCoCrAlYTa coatings and the interdiffusion between the coating and a single crystal substrate in high-temperature oxidation processes were investigated. In this paper, different temperatures, between 900~1100 deg. C, were tested to study the temperature effect on the microstructure evolution and elemental diffusion behavior. The results showed that higher temperature gave quicker oxidation and heavier interdiffusion rate. The response of Al diffusion outwards was fast when enough Al was reserved in the coatings to support the growth of continuous alumina scale. Higher temperature increased the possibility of spinel oxides. The addition of Ta in the coatings increased the stability of gamma'-Ni3(Al,Ta) phase and showed important effects on the microstructure development in the substrate-coating system.