Towards mitigating helium damage in nano-crystal iron and tungsten: a strategy based on the dual trap-channel functionality of grain boundaries tuned by their crystallographic character

Abstract

Nuclear fusion structural materials in critical components like blanket and first-wall are subjected to intense helium (He) generation, causing severe microstructural degradation that limits operational lifetime. Nanocrystalline microstructures have emerged as a promising route toward healing displacement damage. However, the theoretical feasibility of such systems to effectively capture and subsequently expel He through the grain boundary (GB) network remains uncertain, given the intrinsic diversity of GB structures and characteristics. In this work, by combining molecular statics/dynamics simulations with object kinetic Monte Carlo and rate theory, we explore the differentiated behaviors of He at GBs via screening a wide spectrum of ⟨1 0 0⟩ and ⟨1 1 0⟩ symmetric tilt GBs with different characteristics in α-iron (Fe) and tungsten (W). By quantifying three critical energy parameters, including He–GB binding energy, intra-GB migration energy barrier, and He–He binding energy, we demonstrate that GBs exhibit dual functional modes with respect to He accumulation: (i) fast-diffusion channels enabling rapid anisotropic pipe diffusion along specific crystallographic axes and (ii) strong-trapping sinks, characterized by low Frenkel-pair formation energy and deep binding sites that immobilize He. A quantitative relationship between GB structural descriptors (notably local free volume) and key He energetics and kinetics is also established, revealing that atomic/free volume mediates He transport along GBs, thereby clarifying the structural origin of differential He transport/retention across GB types. Furthermore, we systematically discuss the influences of irradiation/thermal defects, as well as alloying elements such as chromium, on He-related functional behaviors of GBs. Based on three governing properties: capture strength, internal diffusivity, and binding stability, this work ultimately provides theoretical foundations for designing GB character-informed He management framework. Within this framework, GB networks can be rationally tailored to simultaneously capture He and facilitate its boundary-mediated expulsion, offering a viable pathway for enhancing the radiation resistance of materials.