Significant suppression of void swelling and irradiation hardening in a nanograined/nanoprecipitated 14YWT-ODS steel irradiated by helium ions

As one of the most promising first wall/blanket structure materials in fusion reactors, oxide dispersion strengthened (ODS) ferritic steel has been extensively studied in past decades. The grain size of ODS steels is often between 200 and 1000 nm, called ultrafine-grained (UFG). Refining their grain size, if possible, should further enhance their radiation tolerance. In the present work, we report on a novel zirconium-doped nanocrystalline (NC) 14YWTZ ODS steel composed of a ferritic matrix with an average grain size of 50 nm and high-density oxide nanoprecipitates with an average diameter of 3.3 nm. Both NC and UFG 14YWT ODS steels were irradiated with helium ions at 450 °C. Abnormal lattice shrinking and narrowing of X-ray diffraction peaks are found in irradiated NC ODS steel. The NC ODS steel has an extremely high sink strength of ∼ 3 × 1016 m−2, which is mainly contributed by grain boundaries and effectively inhibits the aggregation of He atoms and the growth of He bubbles. The bubble size, void swelling, and irradiation hardening in NC ODS steel irradiated at a high dose, when compared to those in UFG ODS steel, are significantly smaller. The underlying mechanisms for the high irradiation tolerance in the NC ODS steel are discussed. This work provides an approach to further enhancing the radiation resistance of conventional UFG ODS steels by refining their grain size to nanoscale dimensions.