A special mechanism of dislocation nucleation in deformed nanocrystalline materials (NCMs) is suggested and theoretically described. The mechanism represents nonlocal homogeneous nucleation of a nanoscale loop of "noncrystallographic" partial dislocation whose Burgers vector magnitude continuously grows during the nucleation process. It is shown that the special mechanism can effectively produce nanoscale loops of lattice and grain boundary dislocations in NCMs deformed at high mechanical stresses.
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