Temperature-dependent evolution mechanism of interface microstructure between gradient MCrAlY coatings and nickel-based superalloy

Gradient MCrAlY coatings exhibited good oxidation resistance during cyclic oxidation at 1200 °C. The interdiffusion behavior between the coating and substrate at 1200 °C exhibited distinct differences compared to that below 1100℃. In this study, the interdiffusion behavior in the gradient MCrAlY/superalloy system was investigated at 1080 °C/1200 °C after cyclic oxidation. To exclude the effect of aluminization on diffusion behavior, interdiffusion behavior between MCrAlY coatings and nickel-based superalloys was also studied at 1080 °C/1200 °C under oxygen-free condition. Based on experiment and thermodynamic calculation, temperature-dependent interdiffusion relationships between Al and Cr were established. The results showed that the diffusion fluxes of Al and Cr were close at 1080 °C. The diffusion flux of Cr could exceed that of Al at 1200 °C, resulting in the formation of the Cr-rich γ phase. The secondary γ' phases precipitated during the cooling of Cr-rich γ phase from 1200 °C. Furthermore, the calculations indicated that increasing Cr in the substrate reduced the diffusion driving force of Al from coating to substrate. This study clarified the role of Cr in interdiffusion and proposed a strategy to reduce the precipitation of TCP phases in gradient MCrAlY/superalloy system at 1200 °C by designing a wide Cr-rich γ phase zone.