Impact of nano-oxides and injected gas on swelling and hardening of 18Cr10NiTi stainless steel during ion irradiation

The radiation performance of 18Cr10NiTi-ODS steel with the addition of Y2O3-ZrO2 nano-oxides was compared with that of non-ODS 18Cr10NiTi austenitic steel in terms of radiation-induced hardening and cavity swelling. TEM observations were performed to evaluate the effect of grain refinement and nano-sized oxide precipitates on microstructural changes and radiation tolerance in specimens exposed to 1.8 MeV Cr3+ or 1.4 MeV Ar+ irradiations over a wide range of temperatures. Formation of homogenously distributed voids was observed in both alloys upon Cr3+ irradiation but the ODS steel exhibited a considerably broader temperature range of void formation and lower overall swelling. Cavity formation in steels irradiated with Ar+ showed a strong dependence on Ar/dpa ratio. Argon addition was found to enhance the nucleation of cavities, which act as point defects sinks that reduce void swelling. The largest swelling resistance was observed in the ODS steel due to the combined effect of mechanical alloying and Ar gas co-injection. The hardening behavior was investigated in both non-irradiated and Ar+ irradiated samples at room temperature and elevated temperatures by means of nano-indentation. Along with the strengthening effect of radiation-induced dislocations, gas-filled nano-cavities strongly contribute to the hardening of irradiated alloys with a tendency to increase the barrier strength of nano-cavities with decreasing cavity size. The ODS variant was found to be somewhat less susceptible to radiation hardening compared to non-ODS 18Cr10NiTi steel.