Atomic structure and dynamic behavior of small interstitial clusters in Fe and Ni

Atomic structure and dynamic behavior of small interstitial clusters (dislocation loops) in Fe and Ni have been studied by means of both the static relaxation method and the molecular dynamics (MD) method in order to clarify their role in the evolution of damage structure during irradiation, especially in the so-called production bias effect through one-dimensional migration and sink efficiency to dislocations. Model crystals were constructed by using N-body potentials and stable atomic structures of small interstitial clusters, i.e., bundle of crowdions were obtained. It was found that each crowdion in the cluster has a split structure when the number of crowdions in the cluster is larger than 10. Dynamic behavior of the loop, e.g., the interaction with a crowdion on a 〈1 1 1〉 loop axis was also investigated as a function of time by the MD method. It was shown that a small interstitial cluster, e.g., I₁₉ in Fe is very mobile under the interaction with a crowdion, which shows that this interstitial cluster I₁₉ has already the property of a dislocation loop of edge character and low Peierls potential for the motion of this loop, which is consistent with the straight edge dislocation in Fe.