Intrinsic diffusion coefficients were calculated for a solid solution binary fcc metal alloy with vacancies using grand canonical and kinetic Monte Carlo methods for a variety of model Hamiltonians. The latter included a kinetically and thermodynamically ideal case, solute-vacancy attraction and repulsion, and solute-solute attraction and repulsion. These model Hamiltonians were chosen to have constant average activation energies in order to focus on contributions from other thermodynamic and kinetic factors. The thermodynamic factor calculated using Monte Carlo was compared to a mean-field regular solution model. It was shown that the mean-field model accurately predicted the thermodynamic factors for each model alloy Hamiltonian except for the alloys with a solute-solute interaction and concentration that were in the spinodal region (as predicted by the regular solution model). The Monte Carlo determined concentration-dependent intrinsic diffusion coefficients were compared to values determined from the dilute five-frequency model and Darken and Manning analytical approximations. The results included that for a solid solution with known average barriers and vacancy concentration, Darken and Manning approximation-based analytic expressions and mean-field theory could be used to predict concentration-dependent diffusion coefficients within a factor of approximately three, provided the system was outside of the spinodal region. The good accuracy of this approximate approach followed from the fact that the thermodynamic factor was the main contribution to the concentration dependence of the diffusion constants, and that this thermodynamic factor was well described by mean-field theory.

Assessing Concentration Dependence of FCC Metal Alloy Diffusion Coefficients using Kinetic Monte Carlo. B.Swoboda, A.Van Der Ven, D.Morgan: Journal of Phase Equilibria and Diffusion, 2010, 31[3], 250-9