Evaluation and modeling of anisotropic stress effect on hydrogen diffusion in BCC iron

The diffusion behavior of interstitial hydrogen in steel should be clarified to reveal the mechanism of hydrogen embrittlement. In this study, we performed molecular dynamics (MD) simulations to elucidate the relationship between various stress conditions and the diffusion coefficients of interstitial hydrogen in body-centered-cubic (bcc) iron. The results revealed that the diffusion coefficients are independent of isotropic stress and exhibit strong anisotropic stress dependence under uniaxial stress along the 〈100〉 direction. The deformation of the atomic structure around the octahedral interstitial site (O site) resulting from stress was examined to elucidate the origin of the anisotropy of the stress dependence. Moreover, a model that predicts the activation enthalpy was derived by quantitatively evaluating the deformation around the O site. The activation enthalpy predicted by the model was consistent with the results of MD simulations when the deformation around the O site was not significant. © 2020 The Society of Materials Science, Japan