Prediction of Hydrogen Diffusion Behavior under the Influence of Defect Structures in Stainless Steel Passivation Film Based on Molecular Dynamics

The excellent corrosion resistance of stainless steel primarily relies on the formation of a dense passivation film on its surface. Stress corrosion and hydrogen embrittlement are the primary forms of damage to the stainless steel passivation film, leading to film rupture and subsequent corrosion of the stainless steel substrate. The passivation film exhibits semiconducting properties and typically consists of a bilayer structure with a chromium-rich inner layer and an iron-rich outer layer. This study employs molecular dynamics simulations to investigate the interaction energy between hydrogen atoms and pristine stainless steel passivation films (Fe₂O₃/Cr₂O₃) as well as those containing three different types of defects and predicts the diffusion processes of hydrogen atoms in passivation films. The results indicate that the strongest interaction energy of -1.4402 eV is observed between hydrogen atoms and the pristine passivation film. However, as defects emerge within the passivation film, the interaction energy decreases, with a minimum energy of -0.1931 eV observed for the film containing chromium vacancies (V_Cr), representing a nearly one-order-of-magnitude reduction compared to the defect-free case. Furthermore, the diffusion coefficients of hydrogen atoms in the three defective passivation films are calculated as 6.437 × 10^-10, 8.249 × 10^-10, and 50.892 × 10^-10 m²/s, respectively. Notably, the presence of a V_Cr defect enhances the hydrogen diffusion coefficient by an order of magnitude compared to the pristine film. Anisotropic diffusion paths and properties are elucidated through an analysis of the self-diffusion behavior of hydrogen in different detective passivation films, providing a theoretical basis for the prediction of hydrogen-induced cracking and the development of early warning technologies for passivation film surface failure.