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The authors formulate a quantitative phase-field model that couples bulk hydrogen diffusion, grain boundary trapping, and anisotropic grain boundary-assisted transport while decoupling numerical interface thickness from physical boundary dimensions. Standard permeation and thermal desorption spectroscopy (TDS) models treat traps as isolated sites, systematically misinterpreting experimental transport kinetics by ignoring boundary connectivity. Benchmark simulations reveal that grain boundary diffusion drives substantial shifts in TDS desorption peaks, showing that conventional Kissinger-type analyses are fundamentally unreliable when grain boundary pathways are active.
Standard Kissinger-type kinetic analyses fail when grain boundary transport is active, as interconnected boundary pathways induce large thermal desorption shifts that isolated-trap models cannot capture.
Grain boundaries influence hydrogen transport in polycrystalline metals by acting as both trapping sites and interconnected diffusion pathways. Conventional interpretations of thermal desorption spectroscopy (TDS) and permeation experiments often treat traps as isolated defects, neglecting grain boundary connectivity and potentially misinterpreting experimental data. Here, we develop a quantitative phase-field model for hydrogen diffusion, grain boundary trapping, and grain boundary-assisted transport. The formulation preserves the physical grain boundary volume independently of the numerical interface thickness and accounts for anisotropic diffusion parallel and perpendicular to grain boundaries. Benchmark simulations verify quantitative behavior under interface upscaling. The model shows that grain boundary diffusion can significantly shift TDS peaks, making Kissinger-type analyses unreliable when grain boundary transport is significant. Effective diffusion coefficients are also shown to depend strongly on grain size, trapping free energy, temperature, and grain boundary mobility. These results highlight the coupled role of trapping thermodynamics, bulk diffusion, and grain-boundary transport.