Atomic-scale effects of hydrogen in iron toward hydrogen embrittlement:: Ab-initio study

We have investigated atomic-scale effects of hydrogen atoms in alpha-Fe by means of ab-initio calculations and examined microscopic mechanism of hydrogen embrittlement in Fe-based materials. Our calculations indicate that accumulation of interstitial hydrogen in a tensile-stress-concentrated region ahead of a crack tip is estimated to be hundredfold increase of the concentration at most, which is much lower than the assumption of the representative models for hydrogen embrittlement. On the contrary, we quantitatively demonstrate that hydrogen significantly facilitates vacancy formation in alpha-Fe and the resultant vacancies trapping hydrogen incline to the ansotropic clusterization. These results suggest considerable contribution of vacancy-related processes to hydrogen embrittlement in those materials, rather than support interstitial hydrogen effects on which the existent models mainly based.