Effects of grain boundaries and nano-precipitates on helium bubble behaviors in lanthanum-doped nanocrystalline steel.

Helium accumulation in advanced nuclear systems would accelerate the failure of structural materials. Nanostructured materials have the potential to mitigate helium effects by providing more nucleation sites for He bubbles. La-doped nanocrystalline 304 austenitic stainless steel (NC304-La) possesses ultra-fine and stable nano-grains ~45 nm in diameter and high-density fine nano-precipitates. In this work, we implanted NC304-La with helium ions, then annealed at different temperatures after implantation. We found that combining the key features of nanocrystalline steels and oxide dispersion-strengthened steels, NC304-La showed excellent bubble swelling resistance. We characterized the interaction between He bubbles and the two features in NC304-La: grain boundaries and nano-precipitates. Through detailed study for the heat-treatment related behaviors of He bubbles in this multi-sink system, the mechanisms of He bubble coarsening resistance in NC304-La were proposed. [Display omitted] [ABSTRACT FROM AUTHOR]