Computer simulation of vacancy segregation during spinodal decomposition and Ostwald ripening

Abstract

It is well accepted that, in most ceramics and alloys, atom diffusion occurs predominantly by the vacancy mechanism rather than the direct exchange mechanism. Therefore, it is expected that the rates of different diffusion processes depend strongly on the number of vacancies in a system. Moreover, most practical systems are inhomogeneous in composition or long-range order. There is an important question about how vacancies are distributed during ordering, phase separation and coarsening in inhomogeneous alloy systems. Recently, one of the author's studied the kinetics of ordering and ordered domain coarsening using the Cluster Activation Method based on the microscopic master equations with atom diffusion described by the vacancy mechanism. Through computer simulation, it was shown that vacancies are strongly segregated into the antiphase domain boundaries during coarsening with vacancy concentration at the boundaries being several to about twenty times higher than that inside the ordered domains. The authors also found that, as expected, the rate of coarsening increases significantly as the overall vacancy concentration increases. However, using a Monte-Carlo simulation technique, Yaldram and Binder found no enrichment of vacancies at interphase boundaries during spinodal phase separation of a binary alloy in a two-dimensional square lattice. In this brief report, themore » authors employ the Cluster Activation Method to study the kinetics of spinodal decomposition using the vacancy mechanism, and in particular, the vacancy distribution during spinodal decomposition and subsequent Ostwald ripening process. For comparison, they use the same Hamiltonian as Yaldram and Binder in their Monte-Carlo simulation of spinodal decomposition with vacancies. The effect of the number of vacancies on the Ostwald ripening process is investigated by artificially introducing different vacancy concentrations.« less