Influence of Two-Vacancy Interactions on Substitutional Solute Diffusion in a fcc Alloy

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Abstract
Two vacancy interactions in the vicinity of a substitutional solute in a fcc metal are considered; equilibrium yields the concentration of divacancies, their motion, and their decomposition as a contribution to solute diffusion. A calculation of the partial correlation factors associated with these configurations is also made. It is found that vacancy attraction to solute atoms is a means whereby the solute diffusivity is enhanced; vacancy-vacancy interactions apparently have little effect. In addition, two vacancy interactions with a single solute atom do not lead to a concentration dependence in the diffusivity. Furthermore, when the divacancy-solute exchange rate becomes large in comparison with the solvent-divancy rate of exchange, these interactions cause the correlation factor to approach zero; the converse situation causes it to rise.