| A new mechanism/mode of plastic deformation occurring through stress-driven rotations of high-angle grain boundaries (GBs) in subsurface areas of nanocrystalline materials is theoretically described. It is demonstrated that a rotation of a high-angle GB produces nanoscale plastic flow and leads to formation of a disclination (rotational defect) whose strength and energy depend on both GB parameters (misorientation angle, etc.) and rotation angle. The suggested approach serves as a generalization of the theoretical model [Bobylev and Ovid'ko, Phys. Rev. Lett. 109, 175501 (2012)] describing stress-driven rotations of low-angle tilt boundaries composed of lattice dislocations in crystals. In the exemplary case of nickel, it is found that the rotations of high-angle GBs are energetically favorable processes in wide range of GB parameters. Each energetically favorable GB rotation is specified by its equilibrium rotation angle φeq associated with the energy minimum. Dependences of φeq on applied stress, GB misorientation and other geometric characteristics of a rotating GB are calculated which show the trends in realization of stress-driven rotations of high-angle GBs in deformed nanocrystalline solids. Our theory is consistent with the corresponding experimental data reported in the literature. |
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