Properties and evolution of sessile interstitial clusters produced by displacement cascades in alpha-iron

Recent molecular dynamics (MD) studies of displacement cascades in a-iron h ave shown that although most self-interstitial atoms are created in the for m of single defects or glissile clusters, sessile clusters are also formed during the quenching stage of a cascade. Statistics on the size and number of sessile interstitial clusters have been determined as a function of casc ade energy and irradiation temperature. The thermal stability of three comm on forms of sessile cluster has been investigated by MD, and the lifetime a nd activation energy for transforming into glissile form have been estimate d. Most sessile clusters transform within a few hundred ps at about 500 K w ith an activation energy of between 0.35 and 0.5 eV. This suggests a re-ass essment of the interpretation of recovery stage II in iron. One type of clu ster having a compact three-dimensional configuration of high symmetry is f ound to be stable for at least 500 ps at temperatures up to 1500 K. The int eraction of sessile clusters with point defects and glissile clusters has b een studied, and the possibility of their subsequent transformation into gl issile clusters is discussed. (C) 2000 Elsevier Science B.V. All rights res erved.