By means of ab initio super-cell calculations based on the density-functional theory, an investigation was made of the stability of H-monovacancy complexes (VHn) and their binding preferences in α-Fe. It was found that VH2 was the major complex under ambient H-pressure conditions, which corrects the conventional model implying the VH6 predominance. It was also demonstrated that monovacancies were not hindered from binding by the H trapping in the case of VH2 predominance. Besides, the presence of H was found to facilitate formations of line-shaped and tabular vacancy clusters without the improbable accumulation. These anisotropic clusters could be closely associated with the fracture planes observed in experiments on H embrittlement in Fe-rich structural materials such as steel. The present results were expected to suggest implications of H-enhanced vacancy activities for the microscopic mechanism of H embrittlement in those materials.

Stability and Clusterization of Hydrogen-Vacancy Complexes in α-Fe - an ab initio Study. Y.Tateyama, T.Ohno: Physical Review B, 2003, 67[17], 174105 (10pp)