A diffusion analysis of transient subsurface γ′-Ni3Al formation during β-NiAl oxidation

Cross-sectional transmission electron microscopy has demonstrated γ′-Ni3Al formation at the alloy/oxide interface during β-NiAl (1 1 0) oxidation under specific conditions. Diffusion analysis was applied to interpret this subsurface phase formation process. It showed that thermodynamically sufficient conditions for phase formation could be achieved with increasing temperature during the early oxidation stage. To stabilize continued γ′ growth, a kinetic requirement needed to be considered, which led to a thickness criterion. The predicted extent of subsurface γ′ phase formation showed good agreement with the experimental observations.