Generation of nanoscale deformation twins at locally distorted grain boundaries in nanomaterials

•Deformation twins can form at locally distorted grain boundaries in nanomaterials.•Cooperative emission of partial dislocations from grain boundaries generates twins.•Twins can form by multiplane nanoscale shear generated at grain boundaries.

Special mechanisms for formation of nanoscale deformation twins at grain boundaries (GBs) in nanocrystalline and ultrafine-grained materials are suggested and theoretically described. Within our description, nanoscale deformation twins are generated at locally distorted GBs that contain local, deformation-distorted fragments being rich in GB dislocations produced by preceding deformation processes. The twin formation mechanisms represent (i) the successive events of partial dislocation emission from GBs; (ii) the cooperative emission of partial dislocations from GBs; and (iii) the multiplane nanoscale shear generated at GBs. The energy and stress characteristics of the nanoscale twin formation through these special mechanisms in nanocrystalline nickel (Ni), copper (Cu) and silicon carbide (3C-SiC) are calculated and analyzed. Competition between the twin formation mechanisms in nanomaterials is discussed.