Vacancy clustering in electron-irradiated FeNiCr austenitic alloys

High purity austenitic FeNiCr alloys have been 3 MeV electron-irradiated at different temperatures (20–773 K). After low fluence irradiations, < 0.01 dpa, vacancy type defects have been investigated by positron lifetime measurements. So, we have noticed that vacancy clusters are present in most of alloys irradiated above room temperature even after irradiation dose as low as 0.0001 dpa. The size of the clusters increases when the irradiation temperature arises, but, in the studied fluence range, the concentration of the aggregates decreases when irradiation is performed at higher temperature. For all experimental conditions, the effect of the chemical composition is studied, the low nickel content alloys (25%) exhibit a strong ability to stabilize and accumulate vacancy type defects. This fact has to be related with a difference in defect migration characteristics observed after a 20 K irradiation which depends on the chemical composition.