Microstructural stability of fcc-γ+B2-β coatings on γ substrate in Ni–Cr–Al system — A phase field model study

A two-dimensional phase field model was employed to examine the evolution of interdiffusion microstructures in ternary Ni–Cr–Al solid-to-solid diffusion couples containing fcc-γ and γ + β (fcc + B2) alloys. Alloys of varying compositions and volume fractions of the second phase (β) were examined to simulate the dissolution kinetics of the β phase (i.e., recession of γ + β two-phase region) observed in γ vs. γ + β diffusion couples. Simulation results showed that the rate of recession of γ + β two-phase region was dependent on the composition of the single-phase γ alloy and the volume fraction of the β phase in the two-phase alloy of the couple. Specifically, the higher the Cr and Al content in the γ alloy and the higher the volume fraction of β in the γ + β alloy lower is the rate of dissolution. Although the volume fraction played a role, the concentration gradients of Al and Cr in the γ phase (e.g., between the matrix of γ + β alloy and single-phase γ alloy) also influenced the recession of the β phase. Simulated results were found to be in good agreement with the experimental observations in ternary Ni–Cr–Al solid-to-solid diffusion couples containing γ and γ + β alloys.