An incipient plastic deformation of several types of grain boundaries subjected to nano-indentation was investigated by atomistic simulations. A previous study had shown that dislocation nucleation in the inner region of the defect-free metals occurs when the resolved shear stress exceeds a particular stress level slightly higher than the ideal shear strength. However, crystal defects such as grain boundaries undermined the nucleation resistance. Here, the dislocation nucleation mechanism at the twin and several coincidence site lattice grain boundaries and the resulting weakening of the dislocation nucleation resistance were examined. It was found that, for the twin and the relatively stable Σ11(¯113)[110] grain boundary, the primary slip deformation was activated on the grain-boundary plane prior to the defect-free region because of the low fault-energy of the grain boundaries during slip deformation. Subsequently, the secondary slip was activated from the grain boundary. On the other hand, the dislocation was initially generated from the heterogeneous grain-boundary plane for the unstable high-energy grain boundaries.

Incipient Plasticity of Twin and Stable/Unstable Grain Boundaries during Nanoindentation in Copper. T.Tsuru, Y.Kaji, D.Matsunaka, Y.Shibutani: Physical Review B, 2010, 82[2], 024101