Effects of atomic size misfit on dislocation mobility in FCC dense solid solution: Atomic simulations and phenomenological modeling

Understanding the interactions between solute atoms and dislocations is essential to developing metallic materials for simultaneously high strength and ductility. Previous studies have majorly focused on the temperature and solute concentration effects on these interactions, excluding the solute atomic size effect; this greatly limits the capacity of design and strength prediction of alloys. In this study, the effects of atomic size misfit on edge dislocation mobility in model random FCC solid solution alloys are investigated by molecular dynamics (MD) simulations. Our results show that dislocation mobilities are atomic size misfit-dependent only when they are larger than a critical value. Additionally, when the atomic size misfit is greater than the critical value, the dislocation motion is controlled by the pinning mechanism. Conversely, when the atomic size misfit is lower than the critical value, the dislocation mobility is unaffected by the solute atoms because of the negligible lattice distortion, however, it is dominated by the phonon drag mechanism as observed in the pure elemental metal. Thus, the drag coefficient, which reflects the dislocation mobility, exhibits different temperature dependences. Based on these observations, a piecewise linear fit relation of the drag coefficient as a function of atomic size misfit and temperature is determined. Finally, the phenomenological dislocation mobility model containing the atomic size misfit and temperature is established. The results can serve to enhance the understanding of solid-solution strengthening effect. The mobility law that derived from the atomic scale can enable accurate DDD simulations at the mesoscale.