Microstructural evolution and element interdiffusion of NiAlHf and NiAlHfY coatings deposited on a Ni-based superalloy

The NiAlHf and NiAlHfY coatings were deposited on a nickel-based single crystal superalloy using arc ion plating technology. The microstructural evolution and element interdiffusion behavior of the NiAlHf and NiAlHfY coatings were investigated under a 1200 °C thermal exposure process. The results showed that the NiAlHfY coating had a higher residual Al content and fewer topologically close-packed (TCP) phases, which implied that Y effectively retarded the diffusion rate of related elements. Besides, the inward diffusion of Al and outward diffusion of Ni lead to a γ → γ´ phase change and the formation of different TCP phases, resulting from the main precipitating elements (Cr, Mo, Re, W, and Ta) having a lower solubility in γ´. Moreover, it is found that the σ and Laves phase precipitate in the interdiffusion zone, which is described by an intergrowth relationship, where the σ phase is a metastable phase and plays a key role in forming the Laves phase. Finally, the interdiffusion mechanism of the elements is proposed.