Single and multiple interstitials in FCC metals

Abstract

Configuration and activation energies and dipole tensors for single and multiple interstitials are calculated by computer simulation using three different potentials for Cu. The single interstitial forms a (100) dumb-bell. The di- and tri-interstitials consist of (100) dumb-bells on nearest-neighbour sites which are respectively parallel and orthogonal to each other. Multiple interstitials are strongly bound but like the single interstitial highly mobile. The tri-interstitial reorientates before it migrates. The binding volumes are relatively small, e.g. about 0.15 Delta V₁ per interstitial atom for the tetra-interstitial. The anisotropy of the dipole tensor is only weakly affected by the choice of the potential, in contrast to the trace (i.e. the volume change). The results are in qualitative agreement with the experimental findings in Al.