Solute influences on void nucleation in magnesium alloys studied by transition interface sampling

Precipitation hardening, a commonly used method for strengthening of alloys, results in materials microstructures that interfere with dislocation slip. Previous studies have shown that interactions between solute atoms and vacancies promotes agglomeration of vacancies into voids. However, this nucleation may involve mutli-stage processes that are not well described by classical nucleation theory. Simulations performed in a Mg-Al system exhibit intermediate metastable states associated with solute-defect clusters. To further explore the hypothesis that solute-vacancy interactions play an important role in promoting void formation, we replace aluminum with yttrium, which is not favored to bind to vacancies, unlike aluminum. Using the Replica Exchange Transition Interface Sampling methodology and molecular dynamics simulations, we have explored the phase space of the void nucleation transition by sampling dynamical trajectories to obtain the activation barrier of the process. The comparison with the Mg-Al alloy barrier is presented and analyzed. We discuss the implications for developing a more accurate void nucleation model that takes solute effects into account.