The structure of small interstitial clusters in b.c.c. metals modelled withN-body potentials

Abstract

The properties of clusters of a small number (≤7) of self-interstitials in bodycentred-cubic transition metals have been studied by computer simulation using model interatomic potentials of the embedded-atom type. The potentials employed are empirically-based and include many-body forces between nearneighbour atoms: they were originally developed by Finnis and Sinclair (1984) and contain recent modifications of the repulsive cores by Ackland and Thetford (1987). The W, α-Fe and Mo potentials have been found to model distinct types of behaviour with regard to preferred cluster geometries, which seem to arise from the relative stability of the possible orientations of the single interstitial. The results are discussed in terms of the Eyre-Bullough mechanism of dislocation loop formation and unfaulting. For the W model a ⟨111⟩ orientation is favoured (even for the single interstitial). For α-Fe the ⟨111⟩ orientation quickly becomes dominant with increased cluster size, while for Mo there is some tendency to form ⟨100⟩ loops, effects which contradict electron microscope observations in irradiated specimens. It is suggested that the N-body empirical potentials are limited in their description of the detailed differences between individual metals.