Solid solution softening in single crystalline metal nanowires studied by atomistic simulations

Abstract

Solid solution strengthening is a common method used in physical metallurgy to increase the strength of metals. However, it is also possible for solute atoms to reduce the strength of metals, known as the solid solution softening effect. In this paper, atomistic simulations were carried out using molecular dynamics and Monte Carlo simulations to explore the softening phenomenon in single crystalline metal nanowires (MNWs) of different alloy systems. It was found that, for single crystalline MNWs, softening is more prominent than strengthening when solute atoms are introduced, which contrasts with the solid solution strengthening that is usually observed in bulk metals. The reduction of unstable stacking fault energy, increase in atomic size misfit, and solute clustering are responsible for this phenomenon, as they facilitate the surface dislocation nucleation in the alloyed nanowires. Additionally, while the nanowire diameter, orientation, surface segregation, and chemical short-range ordering all influence the yield strength, they do not alter the overall softening trend. It is assumed that the softening mechanisms uncovered in this paper are applicable to metallic structures whose yielding is determined by dislocation nucleation.