The influence of impurity trapping on formation and growth of defect clusters in irradiated materials

A number of experimental works have demonstrated that adding a small amount of impurity may significantly alter irradiation induced microstructures in simple alloys and metals. Some of the impurity effects have been attributed to solid solution effect, namely point defect trapping at impurity atoms, and others to various aspects of precipitation effect. This work is intended to clarify how the impurity trapping affects the point defect clustering rates and the defect cluster growth rates, in order to provide theoretical insight to stabilize microstructures of irradiated materials by a minor compositional modification. A comprehensive rate theory model developed by Katoh, Stoller and Kohyama was modified to include point defect trapping processes at solute atoms. The comprehensive model is consisted of a point defect model, which calculates the concentrations of point defects and simple or complex defect clusters in isolated or trapped state, and an extended defect evolution model, most part of which was considerably simplified in this work. Effect of cascade vacancy cluster formation was first investigated, assuming various configurations of the clusters. It was found that cascade vacancy clusters tend to disappear through vacancy emission or SIA collection before they relax into thermally stable configurations such as stacking fault tetrahedra. Employing the calibrated cascade cluster model, point defect evolution under broad range of solute trapping conditions was calculated. Results of calculation on the effects of vacancy trapping energy and initial concentration of solute atoms on point defect and defect cluster evolution, dislocation loop nucleation and cavity development in austenitic Fe-Cr-Ni alloys within temperature range of 623 to 923 K will be provided.