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 c¢ (Ni 3 Al) phase precipitation was investigated in a Ni-Al alloy using the diffuse interface phase field model. The c¢ phase microstructure, coarsening dynamics and interfacial composition width between the c and c¢ phases were studied as a function of the diffusivity magnitude. Increasing the diffusivity results in a reduced number of c¢ nuclei, and accelerated growth and coarsening of the c¢ phase. The cube of the c¢ average radius versus time shows a linear relation during coarsening, and the Al concentration in the c matrix follow the relations Dc c Al $ t À1=3 regardless of the diffusivity magnitude. The c/c¢ interfacial composition width decreases with increased diffusivity and average radius. An obvious Al concentration depleted region is present at the c/c¢ interface during the nucleation and growth stage of c¢ phase indicates that growth occurs by down-hill diffusion in the matrix c phase. That combined with the gradual increase in c¢ composition demonstrates that pseudospinodal decomposition is the transformation mechanism.

A bimodal γ′ phase precipitation in Ni–Al alloys with preaging and continuous cooling: phase-field simulation

“…The chemical free energy density of the Ni-Al alloys can be expressed by f (c, η) = g (c, η) /V m [27][28][29], where V m is the mole volume. The chemical free energy g (c, η) is obtained by using the CALPHAD and the thermodynamic database, written as formula (2) [29,30], where g Al 0 and g Ni 0 is the Gibbs free energy of pure Al and Ni, respectively. L 0 , L 1 , L 2 and L 3 are the interaction parameters of excess free energy, U 1 and U 4 are the bonding energy parameters, they are the functions of temperature [27,31].…”