Comparison of a microstructure evolution model with experiments on irradiated vanadium

A kinetic rate theory model, which includes the formation of cascade-induce d clusters (CIIC), is presented. Comparison of the model to ion irradiation data on vanadium reveals the effects of helium generation and cascade-indu ced interstitial and vacancy clusters on microstructure evolution. The mode l is based on a simplification of hierarchical rate equations for the clust ering of helium bubbles, immobile vacancy clusters, glissile interstitial c lusters, sessile dislocation loops, as well as precipitates and grain bound aries. The model shows that the transport of helium to dislocations, bubble s and grain boundaries is strongly transient because of coupling between th e nucleation and growth modes of bubble evolution. Helium agglomeration in vacancy clusters is shown to reduce the excess vacancy flux to grow matrix and precipitate-affixed bubbles. The direct formation of vacancy and inters titial clusters in cascades reduces the growth rate of bubbles, and leads t o enhanced nucleation of matrix bubbles. In addition to the dislocation and production bias mechanisms, a new mechanism of 'helium nucleation bias' is shown to exist under high helium generation rates. (C) 2000 Elsevier Scien ce B.V. All rights reserved.