Atomic-scale simulations of the mechanical deformation of nanocrystalline metals

simulations of the plastic behavior of nanocrystalline copper. The simulations show that the main deformation mode is sliding in the grain boundaries through a large number of uncorrelated events, where a few atoms ~or a few tens of atoms! slide with respect to each other. Little dislocation activity is seen in the grain interiors. The localization of the deformation to the grain boundaries leads to a hardening as the grain size is increased ~reverse Hall-Petch effect!, implying a maximum in hardness for a grain size above the ones studied here. We investigate the effects of varying temperature, strain rate, and porosity, and discuss the relation to recent experiments. At increasing temperatures the material becomes softer in both the plastic and elastic regime. Porosity in the samples result in a softening of the material; this may be a significant effect in many experiments. @S0163-1829~99!05941-X# I. INTRODUCTION The modeling of the mechanical properties of everyday materials is a very challenging problem. The main difficulty is the vastly different length and time scales at which the various processes occur during deformation—ranging from