Structure and properties of clusters of self-interstitial atoms in fcc copper and bcc iron

Static and molecular dynamics simulations have been used with different typ es of interatomic potentials to investigate the structure, properties and s tability of self-interstitial atom (SIA) clusters produced during irradiati on. In alpha-iron (Fe), faulted clusters of [110] dumbbells are unstable fo r all the potentials. The most stable SIA dusters are sets of parallel [111 ] crowdions. Large clusters of this type form perfect dislocation loops wit h Burgers vector b = 1/2 [111]. Small clusters (less than 9 SIAs) of [100] crowdions are stable at 0 K, but transform into a set of [111] crowdions oi l annealing. Larger [100] clusters are stable and form perfect dislocation loops with b = [100]. Both types of loops are glissile. In copper (Cu), clu sters of parallel [100] dumbbells and [110] crowdions are stable. Large clu sters of these types form faulted and perfect dislocation loops with b = 1/ 3[111] and 1/2[110] respectively. Small faulted clusters (less than 7 SIAs) of irregular shape can transform into a set of [110] crowdions during anne aling. Larger faulted clusters are stable as hexagonal 1/3[111] Frank loops at temperatures of about up to 1050 K for a period of several hundred pico seconds. All faulted clusters are sessile. Clusters of [110] crowdions and 1/2[110] perfect loops are glissile and stable at all temperatures. When la rge enough (more than 49-64 SIAs) they can dissociate on their glide prism. Symmetric three-dimensional clusters of [100] dumbbells are stable at 0 K but during annealing they transform into sets of [110] crowdions. The resul ts for both iron and copper are discussed and compared with experimental da ta and provide a basis for investigating and explaining the observed differ ences in radiation damage accumulation behaviour between fcc and bcc metals .