Atomistic simulations of grain boundary dislocation nucleation

Atomistic simulations are used to investigate dislocation nucleation from symmetric and asymmetric tilt grain boundaries in fee Cu and Al. The use of a 3D periodic bicrystal configuration enables the investigation of how the boundary degrees of freedom impact both boundary structure and dislocation nucleation from these boundaries. Simulation results show that dislocation nucleation from asymmetric tilt grain boundaries requires understanding of the structure and faceting of these boundaries. Deformation simulations under uniaxial tension and compression show entirely different nucleation mechanisms, i.e., nucleation of full dislocations in copper from the grain boundary under compression. The resolved stress normal to the slip plane on which the dislocation nucleates plays an important role in dislocation nucleation for single crystals and interfaces. We further investigate dislocation nucleation from certain twin boundaries, e.g., Sigma 171 vicinal coherent twin boundary in Cu. Simulation results show that the symmetric tilt boundary structure is composed of alternating 1/3 111 disconnections with a dissociated structure in copper. Deformation simulations of a 3D periodic bicrystal configuration under uniaxial tension and compression show very different nucleation mechanisms. Results for various symmetric and asymmetric grain and twin boundaries are summarized.