Temperature and Cr effect on dislocation loop formation in ion irradiated Fe and Fe-Cr model alloys

The development of irradiation-resistant materials is paramount in the realization of advanced fission and fusion reactors. Among the numerous materials considered for this purpose, ferritic-martensitic (F/M) steels emerge as primary candidates due to their multifaceted advantageous properties. However, these F/M steels are not without challenges, particularly in the context of irradiation-induced effects such as hardening due to dislocation loops and irradiation-induced precipitates. Of particular interest in this domain is the persistent inquiry into the mechanisms governing the formation ofdislocation loops within the body-centered cubic (BCC) iron system following irradiation, a question that has remained unresolved for six decades.In this comprehensive research project, ultra-high purity BCC Fe and Fe-Cr model alloys were subjected to irradiation, followed by rigorous examination. The irradiation process involved the use of 6.7-8 MeV self-ions, spanning a wide temperature range from 250°C to 500°C, at two distinctdose levels (0.35 NRT-dpa and 3.5 NRT-dpa), and across three different dose rates ranging from 10-5to 10-3NRT-dpa/s. At lower irradiation temperatures (250°C and 350°C), the predominant effect observed was dislocation loop decoration. Conversely, at elevated irradiation temperatures (450°C and 500°C), self-organizing loops became evident. Notably, at lower damage levels, petal-shaped dislocation loops constituted the primary irradiation-induced defects, while dislocation loop walls predominated at higherdamage levels. Furthermore, a discernible Cr enrichment on the dislocation loops was noted at temperatures exceeding 450°C. This thesis delves into the elucidation of dislocation loop formation mechanisms, with a particular focus onloop formation, as well as the mechanisms underlying Cr segregation in these materials.