2018 年 67 巻 2 号 p. 256-262
The annealing effect on dislocation emission from non-equilibrium grain boundaries (NEGBs) is investigated through atomic simulations of bicrystal models in order to consider why bulk nanostructured metals (BNMs) show the unique mechanical property of “hardening by annealing and softening by deformation” reported by Huang et al. (Science, Vol. 312, pp. 249-251 (2006).). NEGBs with extrinsic grain boundary dislocations (EGBDs) in bicrystal models are annealed at different temperatures. The critical resolved shear stresses (CRSS) to dislocation emission from annealed NEGBs are measured by deformation tests at 0.1 K, and we find that the CRSS increases with the annealing temperature. This result shows the same tendency of “hardening by annealing.” Next, we investigate the controlling factors to the annealing dependence of the CRSS by focusing on the annealing effect on the grain boundary energy, atomic free volume and hydrostatic stress field around the EGBDs. As a result, the structural change of the EGBD core by the annealing process is the dominant cause of the annealing dependence of the CRSS to dislocation emission from NEGBs. Our results show that the plastic phenomenon of dislocation emission from grain boundaries is one of the deformation mechanisms that can explain the unique mechanical property of “hardening by annealing and softening by deformation” in BNMs.