The coupled atomistic/discrete dislocation multi-scale method, which coupled a discrete dislocation continuum region to a fully atomistic region, was used to study screw dislocations which interacted with Σ3, Σ11 and Σ9 symmetrical tilt boundaries in Al. The low-energy Σ3 and Σ11 boundaries absorbed lattice dislocations and generated extrinsic grain boundary dislocations. As multiple screw dislocations impinged on the grain boundaries, the grain-boundary dislocations formed a pile-up along the grain boundary and provided a back-stress that required an increasing applied load in order to push the lattice dislocations into the grain boundaries. Dislocation transmission was never observed; even with large grain-boundary dislocation pile-ups near to the dislocation/ grain-boundary intersection. The results were compared with experiment and with previous related simulations. The Σ9 grain boundary, composed of a more complex set of structural units, absorbed screw dislocations that remained localized, with no grain-boundary dislocation formation. With increasing applied stress, new screw dislocations were nucleated into the opposite grain, from structural units in the grain boundaries that were nearby; but not at the location where the original dislocation intersected the boundary. The detailed behaviour depended upon the precise location of the incident dislocations and the extent of the pile-up. Transmission could occur on both Schmid and non-Schmid planes, and could depend upon the shear stresses on the grain boundary plane. A continuum yield-locus for transmission was deduced. In general, the overall dissociation/transmission behaviour was also governed by the Burgers vectors and the associated steps of the primitive vectors of the grain boundary. The Lee et alia criteria for dislocation transmission were extended in order to account for these factors.

Multiscale Modelling of Dislocation/Grain-Boundary Interactions II - Screw Dislocations Impinging on Tilt Boundaries in Al. M.P.Dewald, W.A.Curtin: Philosophical Magazine, 2007, 87[30], 4615-41