Effect of Diffusivity on the Pseudospinodal Decomposition of the γ′ Phase in a Ni-Al Alloy

Abstract

The effect of diffusivity on pseudospinodal decomposition of γ′ (Ni3Al) phase precipitation was investigated in a Ni-Al alloy using the diffuse interface phase field model. The γ′ phase microstructure, coarsening dynamics and interfacial composition width between the γ and γ′ phases were studied as a function of the diffusivity magnitude. Increasing the diffusivity results in a reduced number of γ′ nuclei, and accelerated growth and coarsening of the γ′ phase. The cube of the γ′ average radius versus time shows a linear relation during coarsening, and the Al concentration in the γ matrix follow the relations \(\Delta c_{\text{Al}}^{\gamma } \sim t^{ - 1/ 3}\) regardless of the diffusivity magnitude. The γ/γ′ interfacial composition width decreases with increased diffusivity and average radius. An obvious Al concentration depleted region is present at the γ/γ′ interface during the nucleation and growth stage of γ′ phase indicates that growth occurs by down-hill diffusion in the matrix γ phase. That combined with the gradual increase in γ′ composition demonstrates that pseudospinodal decomposition is the transformation mechanism.