Stability and clusterization of hydrogen-vacancy complexes in α-Fe:: An ab initio study -: art. no. 174105

By means of ab initio supercell calculations based on the density-functional theory, we have investigated stability of hydrogen-monovacancy complexes (VHn) and their binding preferences in alpha-Fe. We have found that VH2 is the major complex at ambient condition of hydrogen pressure, which corrects the conventional model implying the VH6 predominance. It is also demonstrated that monovacancies are not hindered from binding by the hydrogen trapping in the case of VH2 predominance. Besides, the presence of hydrogen is found to facilitate formations of line-shaped and tabular vacancy clusters without the improbable accumulation. These anisotropic clusters can be closely associated with the fracture planes observed in experiments on hydrogen embrittlement in Fe-rich structural materials such as steel. The present results should suggest implications of hydrogen-enhanced vacancy activities to microscopic mechanism of hydrogen embrittlement in those materials.