High-power Arc Ion Plating γ’-Based Coatings: α/β-Free Design for Oxidation and Interdiffusion Behavior

Abstract

Conventional NiCrAlY coatings primarily consist of α, β, and γ phases. Interdiffusion between the coating and substrate during high-temperature oxidation, along with the associated issue of oxide spallation, has long been a significant concern. In this study, a novel α/β-free γ’ coating was developed, and its oxidation and interdiffusion behavior at 1100 °C was compared with that of a conventional NiCrAlY coating. The oxidation rate constant of the α/β/γ NiCrAlY coating was measured to be 2.4 times that of the γ’ coating, which may be attributed to the doping of reactive elements in the oxide scale promoting oxide growth, while oxide scale spallation further accelerates this kinetic process. The Ta-rich γ’ phase formed at the γ’ coating/substrate interface effectively suppresses the diffusion of substrate elements such as Hf into the coating. Simultaneously, the inherent suppression of α and β phase formation in the γ’ coating is expected to prevent oxide scale spallation induced by phase transformations. Furthermore, a second reaction zone (SRZ) over 50 μm thick was observed beneath the α/β/γ NiCrAlY coating after only 20 h of oxidation, while no SRZ was observed beneath the γ’ coating during oxidation. This significant difference indicates that variations in phase composition directly affect the chemical compatibility between the coating and substrate, thereby playing a crucial role in SRZ formation.