Nucleation of deformation twins on gliding grain-boundary dislocations in nanomaterials

A new micromechanism of nucleating deformation twins in nanocrystalline and ultrafine-grained materials under action of severe mechanical stresses has been proposed and theoretically described. The mechanism is a subsequent splitting of grain-boundary dislocations into lattice partial and sessile grain-boundary dislocations. Ensembles of gliding partial dislocation forms deformation twins. The energy characteristics of this process are calculated. The nucleation of the twins is shown to be energetically profitable and can be athermic (without an energy barrier) under conditions of severe mechanical stress. The dependence of a critical stress at which the barrier-less nucleation of twins took place on the widths of these twins is calculated.