The coarsening and morphology of precipitates were investigated after quenching a dilute binary alloy into its miscibility gap. Three-dimensional kinetic Monte Carlo simulations were performed which were based upon a vacancy-diffusion mechanism. The atomic diffusion model accounted for the asymmetry of the 2 terminal phases with respect to vacancy concentration and diffusivity. It was shown that, at a given low temperature, this asymmetry had a marked effect upon the precipitate coarsening mechanism and the precipitate morphology. In the case of positive asymmetry, where the vacancies diffused mainly within precipitates, precipitate diffusion and coagulation were favored. Almost pure solute precipitates, with atomically sharp interfaces, formed in a persistently supersaturated matrix. In the case of negative asymmetry, where the vacancies diffused mainly in the matrix, the evaporation condensation of solute atoms predominated even in the early stages. The lack of interfacial mobility produced disordered diffuse interfaces, which then resulted in highly supersaturated precipitates.

Vacancy-Assisted Phase Separation with Asymmetric Atomic Mobility - Coarsening Rates, Precipitate Composition and Morphology. J.M.Roussel, P.Bellon: Physical Review B, 2001, 63[18], 184114 (15pp)