In-situ TEM observation of microstructure evolution in Fe9Cr1.5W0.4Si alloy during He+ irradiation and post-implantation annealing

Abstract

The evolution of helium bubbles in a newly developed Fe9Cr1.5W0.4Si alloy that is an important candidate used as fuel claddings in the Lead-cooled fast reactors was in-situ investigated by transmission electron microscopy during 30 keV He+ irradiation at 500 °C and subsequently annealed at 600 °C. Meanwhile, the evolution of dislocation loops was in-situ researched in the initial stage of irradiation. Two mechanisms including the absorption of irradiation defects and the combination of dislocation loops induced the loop growth. Both He+ irradiation and subsequently annealing induced the initiation, migration, aggregation, and growth of helium bubbles, and changed their shape from spherical to preferential faceted. But it was more obvious under the annealing condition. Helium bubbles would preferentially nucleate and grow at dislocation lines and grain boundaries and had large size. The bubble lines formed at dislocation line during helium irradiation, and annealing made them more obvious and larger. A denuded zone with few helium bubbles appeared near grain boundary, but its width decreased with the increase of helium fluence and annealing time. Meanwhile, annealing would lead to the appearance of super large helium bubbles at grain boundaries. The irradiation hardening and swelling were increased with the increase of helium fluence. The corresponding mechanism was analyzed based on in-situ experimental observation.