Coupled grain boundary motion was simulated in a three-dimensional nanocrystalline Al grain boundary network using molecular dynamics. It was shown that, in spite of the triple junction constraints, a symmetrical Σ75 tilt boundary could migrate during the microplastic regime with the same coupling factor as when simulated in a bicrystal configuration. After reaching the full plastic regime, dislocations started to come into play; changing the grain boundary structure and hindering further coupled motion. The above results demonstrated that coupled grain boundary motion, as observed in bicrystal atomistic simulations, could also occurred in a nanocrystalline grain-boundary network during the steep increase in the deformation stress. At larger strains, the condition for strain continuity among the grains called for dislocation slip events. In general, dislocation activity was associated with local stress relief, reflected in the global stress/strain response, which might interfere with the local driving force for coupled grain-boundary motion. The coupling factor that linearly related grain-boundary motion normal to the interface and grain translation perpendicular to the tilt axis, was influenced by deformation and/or accommodation of the three-dimensional grain-boundary network; as shown by the lower coupling factor and the observation that the grain boundary required an applied compressive stress of 250MPa in order to recover its original position. It was expected that these processes would contribute to the hysteresis observed in stress–strain curves.

Coupled Grain Boundary Motion in a Nanocrystalline Grain Boundary Network. M.Velasco, H.Van Swygenhoven, C.Brandl: Scripta Materialia, 2011, 65[2], 151-4