Determination of vacancy and atomic diffusivities in solid solution alloys

Abstract

A Monte Carlo procedure is applied to determine the vacancy and tracer diffusion constants in binary solid solutions. The Monte Carlo method uses vacancy jump frequencies which are calculated using an atomistic simulation method (the First Shell-Black/White model) and are tabulated for all possible jumps in all possible local environments. A simpler, more computationally efficient model, the First Shell-Gray model, is also presented. Comparison of the vacancy diffusion constants, the pre-exponential factors and the migration energies in the Cu-Ni alloys obtained using the First Shell-Gray model and the more accurate but much less computationally efficient Monte Carlo simulation method suggests that the First Shell-Gray model is adequate to predict the diffusion behavior over the entire temperature range. The agreement between the two models is even better at high temperatures where the differences among the Cu jump frequencies and Ni jump frequencies are not as important as at low temperatures. Therefore, treating the atoms in the Cu-Ni alloy as mean-field atoms is an adequate approximation in predicting vacancy and atomic diffusion behavior. The effect of the temperature and alloy composition on the tracer and vacancy correlation factors and the short range order are also investigated. Copyright © 1996 Acta Metallurgica Inc.