A molecular dynamics simulation study of small cluster formation and migration in metals

Molecular dynamics (MD) simulations were performed to investigate the kinetics and energetics of self-interstitial atom (SIA) clusters in vanadium, tantalum and copper. The formation energies of the SIA clusters in all the metals are well represented by a power function with a 0.75 exponent of the cluster size. The cluster diffusivities strongly depend on their structure. In vanadium and tantalum, all the SIA pairs in clusters are located along the 〈1 1 1〉 direction rather than the 〈1 1 0〉 direction. The clusters can migrate one-dimensionally in the 〈1 1 1〉 direction with a small activation energy of around 0.1 eV. In copper, the collective orientation preference of the SIA pairs is not observed indicating that rotation of several pairs in the cluster is required for the cluster to migrate. The activation energy for the rotation is not so high as the cluster migration energy itself. The difference in the SIA cluster migration behavior between bcc and fcc metals is discussed.