Hardening and microstructure evolution of FeCrAl ODS steel under high-energy heavy ion irradiation

This study investigates the influence of nanoscale oxide dispersoid characteristics on irradiation hardening in FeCrAl-based oxide dispersion strengthened (ODS) ferritic steels. Four ODS alloys with systematically varied oxide size and number density—achieved through Al and Zr additions—along with a conventional HT9 steel, were irradiated with 56 Fe ions to 0.8 dpa at 563 K. Vickers micro-hardness tests revealed that the Zr-added and Al-free ODS steels exhibited significantly lower irradiation hardening than their Al-containing counterparts, while HT9 showed the highest hardening. This enhanced radiation tolerance is attributed to the high number density of fine (∼2–10 nm) oxide particles, which act as efficient sinks for point defects, suppressing dislocation loop formation. A power-law correlation was established between the oxide-related sink strength and the irradiation-induced hardness increment. The improved irradiation resistance is primarily attributed to the increased sink strength. Assuming interstitial-type dislocation loops govern hardening, the dispersed barrier hardening (DBH) model yielded predictions consistent with experimental data, confirming the critical role of microstructure in defect mitigation.