Effect of cascade size and damage rate on α’ precipitate stability in Fe-15Cr

Samples of a Fe-15Cr model alloy with an established α' precipitate population were irradiated with 1.25 MeV electrons, 1.5 MeV protons, or 4.4 MeV Fe2+/3+ ions over a range of damage rates to doses of 1 or 10 dpa at 400°C to determine the roles of cascade size and damage rate on the stability of α'. Results showed that α' precipitate size and chromium content increased with dpa for electron irradiations. Proton irradiation also resulted in increases in α' precipitate size and Cr content, but at a slower rate than with electrons due to the influence of ballistic dissolution. Self-ion irradiations caused a reduction in the size and Cr content of α' with dose, and above a threshold damage rate of 1–3 × 10−4 dpa/s, the precipitates were completely dissolved. The ballistic dissolution parameter for self-ion irradiations calculated from both the Nelson-Hudson-Mazey model and a mixing model was in the range 2–5 × 1020 atoms/m2‧dpa compared to a value of ∼9 × 1019 atoms/m2‧dpa for proton irradiation, and explains the different behaviors of the precipitates for these two irradiating particles. Overall, it was found that cascade size strongly determines the stability of α' precipitates and damage rate has its major impact on the rate at which α' precipitates grow or dissolve.