Competing plastic deformation mechanisms in nanophase metals

The mechanisms of plastic deformation in nanocrystalline Ni are studied usi ng three-dimensional molecular-dynamics computer simulations for samples wi th mean grain sizes ranging from 3 to 12 nm under uniaxial load at finite t emperatures. At the lower limit of this size range, we observe a plastic re gime controlled by intergrain sliding; at the upper limit, however, we obse rve a regime with two competing mechanisms: intergrain sliding and dislocat ion emission from the grain boundaries (GB's). The latter mechanism constit utes a transition behavior, precursor to the dislocation-dominated regime t ypical of large grain polycrystals. In samples with mainly low-angle GB's, the transition occurs at a smaller grain size. [S0163-1 829(99)00525-1].