Revisiting the vacancy diffusion behavior under the influence of solute trapping in dilute alloys

Vacancies play crucial roles in various phase transformation processes in metallic solids, but their diffusion behaviors in the presence of solute elements are less known. In this work, the impacts of substitutional solute atoms on vacancy diffusion in dilute alloys are quantitatively studied. Using Al-Sn alloy system as an illustrative case, the detailed vacancy diffusion behavior under the influence of Sn atoms is revealed by atomistic kinetic Monte Carlo simulations. Accordingly, a physics-based analytic model is derived to quantify the influences of substitutional solute atoms on the vacancy diffusivity in dilute alloys. In the model, the diffusion of vacancy is rigorously treated as a combination of free diffusion within host atoms and co-diffusion together with solute atoms. Based on the vibrational frequency, migration enthalpy and binding energy of solute-vacancy pair obtained from first-principles calculations, the time fraction for a vacancy trapping by solute atoms and the corresponding correlation factor of diffusion are derived. The predicted vacancy diffusivity in the show-case Al-Sn alloys at different temperatures shows a good agreement with the diffusivity data extracted from KMC simulations within the five-frequency model framework. By using the analytical model, the retarding effects of different impurity elements on vacancy diffusion in Al alloys are screened and discussed, which will help to further exploit the influences of different solute atoms on vacancies in solid-state phase transformations in the alloys.