Molecular dynamics study of creep mechanisms in nanotwinned metals

Nanotwinned structures have shown great promise as optimal motifs for evading the strength-ductility trade-off. In this paper, we present a study of high temperature creep in polycrystalline nanotwinned face-centered cubic metals using molecular dynamics. The simulations reveal that the nanotwinned metals exhibit greater creep resistance with decreasing twin boundary spacing over a large range of applied stresses. The findings also indicate that the presence of twin boundaries entails higher stress for the onset of power-law creep compared to the nanocrystalline counterparts. Nanotwinned metals with very high density of twin boundaries exhibit a new creep deformation mechanism at high stresses governed by twin boundary migration. This is in contrast to nanocrystalline and nanotwinned metals with larger twin spacing, which exhibit a more conventional transition from grain boundary diffusion and sliding to dislocation nucleation.