The role of grain boundary character on hydrogen energetics and kinetics in tungsten: Insights from atomic-scale modeling

Hydrogen (H) retention in tungsten (W), a critical challenge for its application as a plasma-facing material in nuclear reactors, is strongly influenced by grain boundaries (GBs). However, the precise role of GB in H diffusion and retention, as along with the intricate interactions with H energetics and kinetics, remains poorly understood and contentious yet. In this study, we conduct comprehensive atomistic simulations to explore the effects of GBs on H segregation, desorption, and diffusion in W. Our results reveal that GBs preferentially trap H, with the GB-H binding energies closely related to specific polyhedral structural units. We thoroughly analyze the migration pathways and energy barriers involved in H desorption, determining the critical desorption and decoupling temperatures using a statistical approach. More importantly, the rapid H diffusion channels are identified within GBs that contain discrete dislocation cores and pentagonal bipyramid (PBP) units. Based on these results, we propose a material design strategy that involves tuning GB types and temperature conditions to mitigate H retention. These findings provide essential insights into the energetics and kinetics of GB-H interactions, offering valuable guidance for the design of W-based materials with enhanced resistance to H retention through GB engineering.