Strain softening in nanocrystalline or ultrafine-grained metals: A mechanistic explanation

A mechanism which is based on the formation of residual internal stresses caused by dislocation creation and absorption at grain boundaries is proposed to explain the unique strain softening phenomenon in nanocrystalline and ultrafine-grained metals. With the residual internal stresses caused by plastic deformation in individual grains, in order to create new dislocations at grain boundaries for further plastic deformation, lower external stress is required when compared with that without the residual internal stress field, which results in strain softening.