Atomic-scale simulations of the mechanical deformation of nanocrystalline metals

Nanocrystalline metals, i.e., metals in which the grain size is in the nano meter range, have a range of technologically interesting properties includi ng increased hardness and yield strength. We present atomic-scale simulatio ns 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 a toms) slide with respect to each other. Little dislocation activity is seen in the grain interiors. The localization of the deformation to the grain b oundaries leads to a hardening as the grain size is increased (reverse Hall -Fetch effect), implying a maximum in hardness for a grain size above the o nes studied here. We investigate the effects of varying temperature, strain rate, and porosity, and discuss the relation to recent experiments. At inc reasing temperatures the material becomes softer in both the plastic and el astic regime. Porosity in the samples result in a softening of the material ; this may be a significant effect in many experiments. [S0163-1829(99)0594 1-X].