Stress-driven Rotations of High-angle Grain Boundaries in Nanocrystalline Materials

摘要

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 φ_eq associated with the energy minimum. Dependences of φ_eq 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.