Positron annihilation investigation of hardening behavior induced by Fe2+ irradiation in low-Cr FeCrAl alloys

Compared with 13Cr–FeCrAl alloy, micro-alloyed low-Cr FeCrAl alloy is expected to provide higher potential for application as accident-tolerant fuel (ATF) cladding material. In this study, low-Cr FeCrAl alloys with 7–10 wt.% Cr contents were irradiated to different doses of 1 and 5 dpa at 400 °C with 3 MeV Fe2+ ion. The 13Cr–FeCrAl alloy C35MN developed by Oak Ridge national laboratory was also studied for comparison. Samples were examined by Doppler Broadening of Annihilation Radiation (DBAR) and nanoindentation before and after irradiation. Nanoindentation hardness tests showed that irradiation hardening occurred in FeCrAl alloy samples with different Cr contents after irradiation. The hardening response of the 13Cr–FeCrAl alloy increased with the increase of irradiation dose, while the hardness of low-Cr micro-alloyed FeCrAl alloy changed little or decreased after higher dose irradiation. DBAR shows that the defect type of all samples before irradiation is the same and there are a large number of vacancy-type defects in all unirradiated samples. High temperature irradiation reduces the density of the internal vacancy defect of FeCrAl alloy, which is probably caused by the annealing-induced recovery effect on atomic displacement. The defect density of 13Cr-alloy increases with the increase of irradiation dose, while that of 10Cr–FeCrAl alloy decreases with the increase of irradiation dose. This is related to the much finer grain/precipitate size and the higher number density of precipitates, and thus the higher fraction of boundaries in the 10Cr–FeCrAl alloy. The results also showed that the vacancy recovery rate of the 10Cr–FeCrAl alloy is higher.