Defect-gradient-driven instability of nano-oxides in 12Cr-ODS steels under ion irradiation

This study investigates the stability of nano-oxide particles in fully recrystallized 12Cr oxide dispersion strengthened (ODS) steel under Fe-ion irradiation at 673 K. A pronounced reduction in nano-oxide number density and size distribution was investigated using cross-sectional transmission electron microscopy (TEM). To evaluate the influence of dose-rate gradient effects on nano-oxide behavior, we analyzed two specific regions that received the same dose-rate but differed in gradients: a region at a depth of 450 nm (low dose-rate gradient) and a region at 1000 nm (high dose-rate gradient). Statistical analysis revealed that nano-oxide dissolution was significantly more efficient in the high-gradient region. Kinetic modeling indicated that the dose-rate gradient generates a steep vacancy concentration gradient. This induces directional vacancy fluxes, which enhance the diffusion of yttrium into the matrix and promote oxide dissolution. Additionally, a high density of dislocation loops at the depth of maximum radiation damage likely enhances pipe diffusion, proliferating oxide dissolution. The findings provide new insight into gradient-driven microstructural evolution in ODS steels and contribute to establishing a more comprehensive mechanistic understanding of nano-oxide behavior under irradiation.