Solid solution decomposition mechanisms in cast and microcrystalline Al-Sc alloys: II. Model for the decomposition of a solid solution during the formation of coherent second-phase particles

Abstract

A model is proposed to calculate the kinetic parameters of the precipitation of coherent second-phase particles from a supersaturated solid solution. This model is based on the assumption of barrier-free nucleation of coherent particles. In this case, the decomposition rate of a solid solution and the particle precipitation kinetic parameters are mainly determined by the characteristics of nucleus diffusion growth. The decomposition kinetics of a solid solution during the precipitation of coherent particles is described by the Johnson-Mehl-Avrami-Kolmogorov equation W = 1 − exp[-(t/τ)n], where W is the degree of decomposition and τ = τ0exp(Q/kBT) is the decomposition time. The values of parameters n and Q characterizing the decomposition kinetics are determined. Expressions are derived to describe the dependences of the volume fraction and size of precipitating coherent particles on the supersaturation of a solid solution, the annealing temperature and time, and the thermodynamic and diffusion parameters of a material.