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

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