Uniaxial plastic deformation of polycrystalline Cu with grain sizes in the range of 5 to 20nm was studied by using molecular dynamics computer simulations. A quantitative analysis of plasticity was developed by using localized slip vectors to separate the contributions of dislocation activity from grain boundary sliding. It was concluded that the competition between these two mechanisms depended upon strain rate and grain size, with the dislocation activity increasing with grain size but decreasing with increasing strain rate. For samples with a 5nm grain size, dislocations contributed about 50% of the total plastic strain during steady state deformation at a rate of 108/s, but this fraction decreased to 35% at a rate of 1010/s. When the grain size was increased to 20nm, dislocations accounted for 90% of the strain, even at 1010/s. During the initial stages of plastic deformation, grain boundary sliding initially decreased with strain owing to strain-induced relaxation processes within the grain boundaries. The grains also rotate a few degrees during straining to 20%; the rate of rotation (per unit strain) slightly decreased with strain rate. Lastly, the amount of forced atomic mixing during plastic deformation was computed. The mean square separation distance between atom pairs within grain interiors increased with strain at a rate proportional to their distance apart (i.e., the mixing was superdiffusive), but for pair separations greater than the grain size, this rate became independent of the separation distance.

Quantitative Description of Plastic Deformation in Nanocrystalline Cu - Dislocation Glide versus Grain Boundary Sliding. N.Q.Vo, R.S.Averback, P.Bellon, S.Odunuga, A.Caro: Physical Review B, 2008, 77[13], 134108 (9pp)