Hydrogen accommodation in α-iron and nickel

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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.
Hydrogen, Vacancies, Metals, Atoms, Thermal equilibrium, Energy
Fullarton, M. L., Voskoboinikov, R. E., & Middleburgh, S. C. (2014). Hydrogen accommodation in α-iron and nickel. Journal of Alloys and Compounds, 587, 794-799. doi:10.1016/j.jallcom.2013.10.169