The multidimensional description of evolutionary behavior of the defects in Y-bearing 9Cr-ODS steel with increasing helium irradiation dose

Effective monitoring and prediction of each stage of the helium bubble lifecycle is a fundamental step in addressing the critical issue of helium bubble swelling in advanced nuclear cladding materials. Present study, based on this concept, investigates the evolution of helium bubbles with increasing irradiation fluences in oxide dispersion strengthened (ODS) steel—one of the most promising candidate materials suitable mostly for fusion reactors. Characterization techniques include sub-nanometer spatial resolution positron annihilation spectroscopy (PAS) using slow positron beam Doppler broadening spectrum (DBS), thermal helium desorption spectrum analysis (THDS), and synchrotron-based X-ray probes, such as small-angle X-ray scattering (SAXS) and grazing incidence X-ray diffraction (XRD), providing both quantitative and qualitative descriptions of vacancy-type defects and helium-filled clusters. The ODS steel samples were implanted with 50 keV helium ion to 5 × 10¹⁶/cm², 1 × 10¹⁷/cm², 5 × 10¹⁷/cm², and 1 × 10¹⁸/cm². At low fluences (5 × 10¹⁶/cm², 1 × 10¹⁷/cm²), helium atoms and vacancy clusters are predominantly trapped by oxide nanoparticles, which limit helium bubble growth. The radius of bubbles mainly distributed in the range of ∼1 to 2 nm. In contrast, at high fluences (5 × 10¹⁷/cm², 1 × 10¹⁸/cm²), supersaturated defects and excess helium atoms surpass the trapping capability of oxide nanoparticles, allowing helium–vacancy clusters to coalesce into larger helium bubbles with a broadened size distribution, mainly concentrated in the radius range of ∼2-3 nm. Additionally, substantial helium atoms connected with self-interstitials (SIAs), forming interstitial He-SIAs complexes that exhibit a disc-like accumulation along the (110) crystal plane.