It was recalled that small plate-like clusters of self-interstitial atoms in irradiated metals were extremely mobile. This mobility could be greatly reduced by foreign atoms. Where the plates were large enough to form edge dislocation loops, their immobilization was analyzed as being due to solid-solution hardening. The misfitting substitutional solute atoms could significantly reduce the mobility of small self-interstitial atom loops when in the central cores of their edge dislocation lines. An activation energy was required to unpin a loop from such atoms and this contrary to conventional solid solution hardening – remained finite even when no applied stress drove the dislocation. In dilute solutions, break-away occurred by thermally activated escape from single-atom obstacles on the loops. Application to a proposed fusion power plant alloy showed that the W alloy atoms provided the most severe immobilization, although Mn atoms produced by transmutation were very similar in effect.

Immobilization of Interstitial Loops by Substitutional Alloy and Transmutation Atoms in Irradiated Metals. G.A.Cottrell, S.L.Dudarev, R.A.Forrest: Journal of Nuclear Materials, 2004, 325[2-3], 195-201