Comparison of a microstructure evolution model with experiments on irradiated vanadium

A kinetic rate theory model, which includes the formation of cascade-induced clusters (CIIC), is presented. Comparison of the model to ion irradiation data on vanadium reveals the effects of helium generation and cascade-induced interstitial and vacancy clusters on microstructure evolution. The model is based on a simplification of hierarchical rate equations for the clustering of helium bubbles, immobile vacancy clusters, glissile interstitial clusters, sessile dislocation loops, as well as precipitates and grain boundaries. The model shows that the transport of helium to dislocations, bubbles and grain boundaries is strongly transient because of coupling between the 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 interstitial clusters in cascades reduces the growth rate of bubbles, and leads to enhanced nucleation of matrix bubbles. In addition to the dislocation and production bias mechanisms, a new mechanism of `helium nucleation biasʹ is shown to exist under high helium generation rates.