Self-blocking driven interstitial confinement at metallic grain boundaries

• As accumulated SIAs progressively occupy GB trapping sites, subsequent incoming SIAs near GBs enter metastable states, forming a self-blocking region that limits further SIA absorption. • The blocked SIA clusters near GBs exhibit dual functionality: enhanced vacancy annihilation within several atomic layers of GBs and long-range repulsion effects on bulk SIAs. • This SIA self-blocking phenomenon occurs mainly at low temperatures, implying both a saturation threshold for GB defect absorption capacity and an extended boundary zone facilitating vacancy–SIA recombination. Grain boundaries (GBs) serve as critical microstructural features in determining the radiation resistance of nanocrystalline metals through their capacity to absorb radiation-induced defects, particularly self-interstitial atoms (SIAs) and vacancies (Vs). Nevertheless, the fundamental mechanism governing SIA dynamics near GBs that dominate defect–GB interactions remain inadequately elucidated. This knowledge gap is primarily due to the fact that the time scale of SIA diffusion and its segregation towards GBs is significantly smaller than that of other events, leading to its preferential segregation to GBs and decoupling from other defects. In this study, we employ combined molecular statics and dynamics simulations to systematically investigate the atomic-scale behavior of SIA and its cluster (SIA n ) states near GBs in three body-centered cubic metals (tungsten, molybdenum and iron), while concurrently exploring potential V annihilation mechanisms associated with these processes. We propose a “self-blocking” mechanism governing the behavior of the SIA n near GBs at low temperatures. As accumulated SIA n s progressively occupy GB trapping sites, subsequent incoming clusters experience spatial confinement within the near-boundary region. These constrained SIA n s exhibit intermediate energy states between bulk configuration states and fully GB-trapped states. Crucially, the partially constrained SIA n s demonstrate two distinctive features of an enhanced V annihilation volume exceeding that of GB-trapped clusters by several times (attributed to their preserved bulk-like atomic configurations) and long-range repulsive interactions with bulk SIAs (potentially modifying defect-trapping dynamics of GBs). This self-blocking phenomenon implies both a saturation threshold for GB defect absorption capacity and an extended boundary zone facilitating V–SIA recombination. The spatially confined annihilation pathway near GBs provides a potential channel for eliminating bulk defects at low temperatures, offering new insights into the atomic-scale self-healing processes in nanocrystalline materials.