It was recalled that self-interstitial atoms and self-interstitial atom clusters were produced in displacement cascades during irradiation with high-energy particles. The migration kinetics of such defects were then a critical factor in controlling microstructural evolution. Extensive molecular dynamics simulations were made here of the diffusion of the self-interstitial atom and its clusters in body-centered cubic Fe. Diffusivities were calculated for various self-interstitial atom cluster sizes. It was found that, although the diffusivity itself decreased as the self-interstitial atom cluster size increased, the activation energy for migration was very small and did not increase with size; in contrast to previous assumptions. A study was made of the mechanism of single self-interstitial atom diffusion by using a kinetic Monte Carlo technique. The resultant model was consistent with experiment. An important observation was that the effective migration energy of the single self-interstitial atom (0.17eV in the case of the present Monte Carlo study) was smaller than the activation energy for IE-stage recovery. The proposed model explained all of the details of the low-temperature ID and IE recovery stages of body-centered cubic Fe, without having to assume the existence of 2 independent interstitial configurations.

Migration Kinetics of the Self-Interstitial Atom and its Clusters in BCC Fe. N.Soneda, T.Diaz de la Rubia: Philosophical Magazine A, 2001, 81[2], 331-43