Immobilization of interstitial loops by substitutional alloy and transmutation atoms in irradiated metals

Small platelike clusters of self-interstitial atoms (SIAs) in irradiated metals are extremely mobile. This mobility can be greatly reduced by foreign atoms. Where the plates are large enough to form edge dislocation loops, their immobilization is analysed as a solid solution hardening. The misfitting substitutional solute atoms can significantly reduce the mobility of small SIA loops when in the central cores of their edge dislocation lines. An activation energy is required to unpin a loop from such atoms and this – unlike in conventional solid solution hardening – remains finite even with no applied stress driving the dislocation. In dilute solutions break-away occurs by the thermally activated escape from single atom obstacles on the loops. Application to a proposed fusion power plant alloy (EUROFER 97) shows that the W alloy atoms provide the most severe immobilization, although Mn atoms produced by transmutation run a close second. The contribution of Cr is evaluated.