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 have shown that although most self-interstitial atoms are created in the form 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 cascade energy and irradiation temperature. The thermal stability of three common forms of sessile cluster has been investigated by MD, and the lifetime and activation energy for transforming into glissile form have been estimated. Most sessile clusters transform within a few hundred ps at about 500 K with an activation energy of between 0.35 and 0.5 eV. This suggests a re-assessment of the interpretation of recovery stage II in iron. One type of cluster having a compact three-dimensional configuration of high symmetry is found to be stable for at least 500 ps at temperatures up to 1500 K. The interaction of sessile clusters with point defects and glissile clusters has been studied, and the possibility of their subsequent transformation into glissile clusters is discussed. (C) 2000 Elsevier Science B.V. All rights reserved.