The influence of helium and heavy ion irradiations on radiation responses of single crystal Cu with nanovoids : An in situ TEM study

Helium is a common nuclear reaction product, and it plays an important role in radiation-induced void swelling. Although extensive studies have been conducted to investigate the helium effects in metals and alloys, most of them were based on the post-irradiation analyses or computer simulations. Conclusive evidence that can demonstrate how voids evolve in the presence of He under high-temperature radiation remains limited. In this work, we performed in situ heavy ion radiation studies in a transmission electron microscope to compare the radiation response of the preexisting nanovoids in single crystal copper subjected to a single beam of 1 MeV Kr ions and a sequential dual beam of 14 keV He ion and 1 MeV Kr ion at 350 °C. Our studies revealed that the nanovoids would contract continuously until being eliminated when irradiated by a single beam of Kr ions. In comparison, the nanovoids in helium-injected Cu could reach a stable state and eventually stopped shrinking. Moreover, the influence of helium on the kinetics of void/bubble evolution under heavy ion irradiation was discussed within the framework of a proposed critical bubble model and bubble coarsening model.