Grain-boundary-enhanced re-precipitation of oxide nanoparticles in ion-irradiated nanocrystalline 14YWT-ODS steels

The evolution of oxide particles in oxide dispersion strengthened (ODS) steels subjected to high temperature radiation is critical for maintaining their radiation resistance since the particles were damaged. Conventional ODS steels are often ultrafine-grained (with a grain size between 100 and 1000 nm), and the nanoparticles coarsen and their density decreases after ion irradiation. In this work, nanocrystalline (NC) ODS steels (with an average grain size of 50 nm) and ultrafine-grained (UFG) ODS steels (with an average grain size of 250 nm) were irradiated with 6 MeV Au ions at 500 °C up to 468 dpa. The nanoparticles in NC steels showed a slight decrease in diameter and an increase in number density, exhibiting completely reverse evolutions with respect to UFG steels under the same radiation conditions. The reverse evolution can be reasonably explained by the competition between radiation-driven ballistic dissolution and nanograin-localized long-range diffusion, leading to the partial conversion of Y4Zr3O12 to Y2Zr2O7. This work expands the strategy to stabilize the remaining nanoparticles in ODS alloys under radiation via nanocrystalization.