Helium bubble formation in nickel under in-situ krypton and helium ions dual-beam irradiation

Abstract

Helium has profound effects on the microstructure and mechanical property of materials used in nuclear power systems. To understand the interaction between helium and irradiation-induced defects and its effect on bubble formation, single-beam and dual-beam irradiations on nickel were performed with 16 keV helium ions and 1 MeV krypton ions under in-situ TEM observation. For 1 MeV krypton single-beam irradiation, voids were observed at 600 °C but not at 500 °C and 700 °C. For helium single-beam irradiation at 500 °C, helium moved freely and formed bubble-loop complexes. For dual-beam irradiation at 500 °C, helium was trapped by vacancies and formed bubbles homogeneously. The structure of dislocation loops was also affected by the presence of helium. For krypton single-beam irradiation at 500 °C, the microstructure was {100} periodic wall of faulted and perfect dislocation loops. For dual-beam irradiation at 500 °C, periodic wall was not observed, and dislocation loops were predominantly perfect. For single-beam helium at 500 °C, dislocation loops were produced by athermal process of SIAs ejection or loop punching mechanisms. The interplay between helium and vacancies played an important role on the evolution of helium bubbles and defect microstructures.