Carbon vacancy network mediated hydrogen trapping at the α-Fe/VC interface

Hydrogen embrittlement poses a significant threat to the structural integrity of high-strength steels. Although vanadium carbide (VC) precipitates are recognized as effective traps for mitigating hydrogen-induced damage, the precise mechanisms of hydrogen trapping and diffusion within VC remain controversial. In this study, we employ first-principles calculations to investigate the influence of carbon vacancies on hydrogen trapping and diffusion behavior at the coherent α-Fe/VC interface. Our results reveal that interfacial carbon vacancies facilitate hydrogen approach along the xy-plane, while interconnected vacancy networks enable hydrogen to diffuse from the α-Fe matrix into the VC bulk. Notably, hydrogen ingress into VC occurs preferentially through nearest-neighbor carbon vacancies. The calculated activation energies for hydrogen escape from interfacial and internal VC vacancies are 67.5 kJ mol^-1 and 82.2-83.9 kJ mol^-1, respectively, in good agreement with experimental values. These findings underscore the critical role of interfacial and connected carbon vacancies in mediating hydrogen diffusion and trapping within VC, providing atomistic insights for designing hydrogen-resistant steels.