Molecular dynamics methods were used for the simulation of polycrystalline plasticity and for the study of the interplay between dislocations and grain-boundary processes during room-temperature plastic deformation of model nanocrystalline microstructures. The simulations revealed that, under relatively high stresses (2.5GPa) and at large plastic strains (12%), extensive deformation twinning took place; in addition to deformation via

dislocation-slip mechanisms. The heterogeneous and homogeneous nucleation of deformation twins was observed. The heterogeneous mechanism involved the successive emission of Shockley partials from the grain boundaries onto neighboring slip planes. The homogeneous process took place in the grain interiors, via a nucleation mechanism which involved dynamic overlap of the stacking faults of intrinsically and/or extrinsically dissociated dislocations. The simulations also revealed the mechanism of formation of a new grain via the interplay between deformation twinning and dislocation nucleation from the grain boundaries during deformation. The tendency to deformation twinning in the simulations was found to be surprising, because the process had never been observed in coarse-grained Al, and the well-known pole mechanism could not operate in such a small grain size.

Deformation Twinning in Nanocrystalline Al by Molecular-Dynamics Simulation. V.Yamakov, D.Wolf, S.R.Phillpot, H.Gleiter: Acta Materialia, 2002, 50[20], 5005-20