Microstructural evolution of neutron-irradiated Fe-Cr-Ni ternary alloys at high helium generation rates

Abstract

A series of Fe-Cr-Ni ternary alloys were irradiated to 12–14 dpa in the Oak Ridge Research Reactor (ORR). In this experiment, most of the helium atoms were produced by the 58Ni(n, γ) 59Ni(n, α) 56Fe sequential reaction, and, therefore, the helium generation rate was almost proportional to the nickel content, ranging from 27 to 58 appm He/dpa in 20 to 45 wt% Ni alloys. Irradiation temperatures were 330, 400, 500 and 600°C, and the specimen variables were the nickel level, the chromium level and cold-working. The high levels of helium, combined with details of the temperature history, were found to have dominated to microstructural development, sometimes overwhelming and even reversing the action of a given material variable. Microscopy examination showed that there was an unprecedented refinement of cavity microstructure at all temperatures, which accounts for the substantial alterations in both swelling and mechanical properties observed in earlier studies.