Characterization of oxide nanoprecipitates in an oxide dispersion strengthened 14YWT steel using aberration-corrected STEM

The structure and chemistry of nanoprecipitates in an oxide dispersion strengthened (ODS) 14YWT steel were systematically investigated by means of aberration-corrected scanning transmission electron microscopy. We found that the crystal structure of the nanoprecipitates depends on the particle size, while the compositional difference is insignificant. Large nanoparticles (∼10-30 nm in diameter) have a long period NaCl-based structure including TlI-type stacking, while the small nanoparticles (<5 nm) possess the NaCl-based structure with a high density of lattice defects. The size-related structural difference between small and large nanoparticles reveals the structural origins of the unusual thermal stability of the nanoprecipitates, as well as the extraordinary mechanical properties of ODS steels.