Microstructural development of a heavily neutron-irradiated ODS ferritic steel (MA957) at elevated temperature

Microstructural observation was performed on a neutron-irradiated oxide dispersion strengthened (ODS) ferritic steel with emphasis on oxide behavior, including phase stability under irradiation at elevated temperature (∼973 K). Transmission electron microscopy observation of the Y–Ti complex oxide particles showed they were fine (∼40 nm) whereas the Ti-oxide particles were relatively coarse (∼300 nm). Dispersion parameters of oxide particles, such as mean size and number density, changed due to irradiation. This implies recoil resolution of the oxide particles. When irradiated at 973 K, some Y–Ti complex oxides survived and interacted with the dislocation structures, which delayed the dislocation recovery and stabilized the elongated grain structure. It is considered that oxide particles could be effective pinning points of dislocations in motion under irradiation to a dose of ∼100 dpa.