摘要
The performance of plasma-facing components in nuclear fusion reactors is limited by radiation-induced degradation, particularly helium accumulation and transport. High-entropy alloys (HEAs) have shown enhanced irradiation tolerance, yet the physical origin remains debated. We argue that conventional barrier-based models cannot fully explain helium cavity growth and migration observed in HEAs. Therefore, we explore a new framework for studying helium diffusion by investigating its pathways in a body-centered cubic refractory HEA (MoNbTaVW), a medium-entropy alloy (MoNbTa), and reference Ta, using ion implantation, isochronal annealing, transmission electron microscopy, elastic recoil detection analysis, and atomistic simulations. We show that increased elemental diversity leads to increasingly tortuous He diffusion pathways, resulting in persistent local mobility but reduced effective long-range redistribution relative to Ta and MoNbTa. Atomistic simulations reveal that helium preferentially probes local potential-well volumes associated with group-5 transition elements (V, Nb, Ta), resulting in highly tortuous trajectories characterized by short step lengths and frequent directional changes. This pathway-level confinement could explain the experimentally observed coexistence of large local helium cavities and limited long-range transport in the damage-peak region. These results provide a trajectory-based perspective for understanding diffusion in HEAs under irradiation.
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