Irradiation damage of nickel in a high-voltage electron microscope

Abstract

Electron irradiation damage in high-purity annealed and 20% deformed nickel has been studied using a high-voltage electron microscope (HVEM) operating at 650 kV. The effects of temperature of irradiation, electron dose and cold work on point-defect clustering in general and void formation in particular have been investigated. Both faulted and unfaulted dislocation loops were observed during irradiation at 240 to 500°C; multilayer dislocation loops were observed at the higher temperatures. Voids exhibited a cubic shape at low dose with a nearly homogeneous distribution in annealed and an inhomogenous distribution in 20% deformed nickel. The average void size for annealed nickel was larger than that for 20% deformed nickel and the void growth rate was found to be higher for annealed nickel. In annealed nickel, the void concentration increased up to ≈14 dpa and then decreased, while in 20% deformed nickel it increased up to ≈35 dpa. Swelling was considerably reduced by cold work compared to annealed nickel. These observations are discussed with emphasis on the role of dislocation density in the nucleation and growth of voids and swelling.