Hydrogen and vacancy concentrations in a-iron under high hydrogen gas pressure and external stress: A first-principles neural network simulation study

SH Zhang and SH Zhu and FS Meng and S Ogata, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, 90, 246-256 (2024).

DOI: 10.1016/j.ijhydene.2024.09.378

The metal-hydrogen-vacancy interaction in a-iron is crucial for understanding hydrogen embrittlement behavior and developing reliable materials for green gaseous hydrogen applications; however, it remains underexplored, particularly in contexts involving external stress and high hydrogen gas pressure. In this study, we performed quantitative analyses of metal-vacancy-hydrogen interactions in a-iron, measured by hydrogen solubility and the thermodynamics of vacancy-hydrogen complexes, under such challenging conditions using a reliable first- principles neural network potential. High hydrogen gas pressures reaching up to 2 GPa were investigated. As the atomic concentration surpasses approximately 0.01, hydrogen solubility is dominated by hydrogen-induced lattice distortion (primarily volumetric expansion) and the interactions between hydrogen atoms within the metal matrix, resulting in significant deviations from Sieverts' law. Our results reveal a significant effect of shear stress on hydrogen solubility, deviating from previously used equations. Moreover, the influence of external stress on the thermodynamics of the vacancy-hydrogen complex, particularly vacancy formation free energy, is uniquely characterized by hydrogen solubility, regardless of the external stress magnitude. It thereby offers a rapid method to estimate the vacancy properties under external stress based on readily accessible external-stress-free data.

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