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 a mount of impurity may significantly alter irradiation induced microstr uctures in simple alloys and metals. Some of the impurity effects have been attributed to solid solution effect, namely point defect trappin g at impurity atoms, and others to various aspects of precipitation ef fect. This work is intended to clarify how the impurity trapping affec ts the point defect clustering rates and the defect cluster growth rat es, in order to provide theoretical insight to stabilize microstructur es of irradiated materials by a minor compositional modification. A co mprehensive rate theory model developed by Katoh, Stoller and Kohyama was modified to include point defect trapping processes at solute atom s. The comprehensive model is consisted of a point defect model, which calculates the concentrations of point defects and simple or complex defect dusters in isolated or trapped state, and an extended defect ev olution model, most part of which was considerably simplified in this work. Effect of cascade vacancy cluster formation was first investigat ed, assuming various configurations of the clusters. It was found that cascade vacancy clusters tend to disappear through vacancy emission o r SIA collection before they relax into thermally stable configuration s such as stacking fault tetrahedra. Employing the calibrated cascade cluster model, point defect evolution under broad range of solute trap ping conditions was calculated. Results of calculation on the effects of vacancy trapping energy and initial concentration of solute atoms o n point defect and defect cluster evolution, dislocation loop nucleati on and cavity development in austenitic Fe-Cr-Ni alloys within tempera ture range of 623 to 923 K will be provided.