Hydrogen accommodation in α-iron and nickel

Abstract

Ab initio calculations have been used to study the effects of hydrogen on vacancy concentrations in αα-Fe and Ni. The presence of H interstitials aided vacancy formation in both metals but via two different mechanisms. In αα-Fe, trapping of H by a vacancy is favourable. However binding of further hydrogen atoms was not predicted to proceed. The thermal equilibrium concentration of H interstitials in comparison to vacancies in αα-Fe is many orders of magnitude higher over a wide temperature range. Excessive H interstitials in solid solution facilitate vacancy formation, lowering the required energy by 0.79 eV (down to 1.41 eV). In Ni, a single H interstitial is not expected to have an impact on the vacancy population, increasing the vacancy formation energy by 0.32 eV. Two bound H interstitials however are predicted to decrease the vacancy formation energy by 0.52 eV with expected arrangement along a 〈〈1 1 1〉〉 direction around the vacancy. The calculations show reasonable agreement with experimental data when comparing crystal lattice contractions of the pure metals and predicted melting temperature of the Me–H alloys. © 2013, Elsevier B.V.