Density Functional Theory-Based Investigation of Adsorption, Permeation, and Desorption of Hydrogen Isotopes in Fe-Cr Alloy of Varied Compositions.

A fundamental understanding of hydrogen behavior in Fe-Cr alloys is critical for mitigating hydrogen-related challenges in fusion and fission reactor environments. Extensive calculations are performed using plane-wave density functional theory to investigate the interaction and dynamics of hydrogen isotopes in a model bcc Fe-Cr system. The hydrogen dissociative adsorption on Fe-Cr surfaces is found to be exothermic, whereas absorption into subsurface and bulk sites is shown to be endothermic. The findings reveal that the tetrahedral-site absorption energies for hydrogen become increasingly endothermic with rising Cr concentration. Nudged elastic band (NEB) calculations show that the predicted diffusion barriers of hydrogen isotopes increase with Cr content and thus reduce the permeation. The computed diffusion, permeation, and solubility trends agree with the experimental results. The analysis of hydrogen isotopes highlights the role of zero-point energy in governing the desorption kinetics of hydrogen.