Dose dependence of ion irradiation effects on 12Cr–6Al-ODS steel with electron-beam weld line

Abstract

Oxide dispersion strengthened (ODS) steels are promising accident tolerant fuel (ATF) cladding alternatives because of their excellent oxidation resistance and mechanical properties at high temperatures. Coupons of 12Cr–6Al-ODS steel with an electron-beam (EB) weld line were irradiated with 6.4 MeV Fe3+ ions at 300 °C to nominal doses of 2.6, 7.9 and 13.0 dpa at 600 nm depth below the irradiated surface. Transmission electron microscopy (TEM) and nano-indentation tests were performed after ion irradiation to investigate the post-irradiation microstructures including the stability of oxide nanoparticles and the irradiation induced hardening, respectively, with special attention paid to the comparison between base metal and EB weld line. Oxide nanoparticles in base metal were stable under present irradiation conditions as no significant change was observed with respect to the average diameter and number density. A similar trend was recognized for the oxides in EB weld line. As for irradiation-induced dislocation loops, EB weld line exhibited larger average diameter and higher number density than base metal. And the average diameter of dislocation loops increased with increasing irradiation dose, while the number density appeared to peak at an intermediate dose of 7.9 dpa, irrespective of in base metal or EB weld line. Irradiation hardening was estimated by two different methods, so called bulk hardness by Nix-Gao model and the reference depth hardness at an indentation depth of 225 nm. Both methods showed a higher irradiation hardening in EB weld line than in base metal irrespective of irradiation dose, and hardening saturation was noted in EB weld line. The estimated hardening by dispersed barrier hardening (DBH) model was consistent with the measured hardening, suggesting that the irradiation hardening could be mainly attributed to the formation of dislocation loops with different Burgers vector.