A combined cluster dynamic/kinetic Monte Carlo model for precipitate nucleation in interstitial/substitutional alloys

Abstract

The mechanism of precipitate nucleation in interstitial/substitutional multi-component alloys is still not well understood. Therefore, an atomistic simulation model has been developed to gain elementary understanding of the process and to provide some quantitative information on the nucleation kinetics. The present model assumes that the precipitate (cluster of atoms of a stoichiometric phase) is formed at a fixed nucleation center. The size of the cluster evolves as a consequence of fluctuations of the fast diffusing interstitial atoms, determined by stochastic absorption and emission processes. Simultaneously, slowly diffusing substitutional alloying elements are attracted by the clusters, which can significantly influence the nucleation barrier. The cluster size fluctuations are treated in the framework of cluster dynamics. Diffusion of substitutional atoms is treated by the kinetic Monte Carlo method. Both stochastic and statistical methods are applied to simulations of nucleation of cementite in the Fe-Cr-C system.