Speaker
Description
Ion implantation at 500°C into bcc Fe–Cr model alloys offers a controlled non-equilibrium platform to dissect the physics of Y–Zr–O nano-oxide nucleation and evolution in oxide-dispersion strengthened (ODS) steels for nuclear applications, simultaneously delivering chemical supersaturation of low-solubility Y/Zr solutes and high-damage collision cascades within a ~100 nm surface layer that store excess free energy as mobile point defects and cascade remnants driving radiation-enhanced diffusion and heterogeneous nucleation on dislocation loops and collapse sites. Advanced TEM/STEM analysis shows that Y–Zr–O nano-oxides form through fast, non-equilibrium processes, producing different crystal structures—fluorite-type (like YSZ), pyrochlore-related, and triclinic Y₄Zr₃O₁₂—with distinct HRTEM/FFT patterns that reveal their atomic arrangement, along with some preferred matrix/oxide orientation relationships that reduce elastic strain energy. HAADF-STEM Z-contrast imaging reveals bright Y/Zr-enriched within precipitates that show clear Fe/Cr depletion relative to the surrounding matrix, while EDS chemical mapping and quantification establish precise Y:Zr:O stoichiometries ranging from ~1:1 to 1:3—together providing definitive proof of discrete, chemically-distinct oxide phases rather than mere solute segregation or clustering. Mechanical polishing creates surface dislocations that favor shallow nucleation (skewed profiles, broad sizes), while twin-jet electropolishing yields uniform subsurface oxides. This surface scales trap solutes or block O-transport, tuning stoichiometry. At 500°C, fast oxygen diffusion stabilizes early Y/Zr–O clusters whose structure follows local cascade geometry, not equilibrium phase diagrams.