Flux effects in precipitation under irradiation – Simulation of Fe-Cr alloys

Abstract

Radiation-enhanced precipitation of Cr-rich α′ in irradiated Fe-Cr alloys, which results in hardening and embrittlement, depends on the irradiating particle and the displacement per atom (dpa) rate. Here, we utilize a Cahn-Hilliard phase-field based approach, that includes simple models for nucleation, irradiating particle and rate dependent radiation-enhanced diffusion and cascade mixing to simulate α′ evolution under neutrons, heavy ions, and electron irradiations. Different irradiating particles manifest very different cascade mixing efficiencies. The model was calibrated using neutron data. For cascade inducing neutron/heavy-ion dpa rates at 300 °C between 10−8 and 10−6 dpa/s the model predicts approximately constant number density, decreasing radius, decreasing α′ Cr composition, and lower α′ volume fraction. The model then predicts a dramatic transition to no α’ formation above approximately 10−5 dpa/s, while electron irradiation, with weak mixing, has little effect at dpa rates up to 10−3 dpa/s. These model predictions are consistent with experiments. We explain the results in terms of the flux dependence of the radiation-enhanced diffusion, cascade mixing, and their ratio, which all vary significantly in relevant flux ranges for neutron and cascade inducing ion irradiations. These results show that both cascade mixing and radiation-enhanced diffusion must be accounted for when attempting to emulate neutron-irradiation effects using accelerated ion irradiations.