Adapted solute drag model for impurity-controlled grain boundary motion

In this study, impurity segregation and solute drag effects on grain boundary (GB) motion were investigated in a binary Al-Ni model system with an inclined Σ5 GB by direct molecular dynamics simulations. By extending the interface random walk method to impure systems, it was found that the GB mobility was significantly influenced by the segregated impurities, which generally decreased as the impurity concentration increased. Moreover, based on simulations at different temperatures and impurity concentrations, we validated that the solute drag effects can be well modeled by the theory proposed by Cahn, Lücke, and Stüwe (CLS model) more than 50 years ago, provided that proper adaptations were made. In particular, we found that in strongly segregated GB system, the boundary mobility was deeply correlated to the impurity diffusivity in the direction perpendicular to the boundary plane in the frame of the moving boundary, instead of the impurity bulk diffusivity assumed in the original CLS model and many past studies.