First-principles energetics of hydrogen traps in α-Fe: Point defects

We performed a series of density functional theory (DFT) calculations to quantify the binding energy of hydrogen to a number of point defects in body-centered cubic Fe, e.g. vacancies, interstitial carbon and substitutional solutes. We found the following: (i) Vacancies are the strongest H trap, with a binding energy of 0.57 eV. (ii) The binding energy of H to C is 0.09 eV. (iii) Most substitutional solutes (except Si, Cr, Mn, Co, and Mo) trap H with positive binding energies up to 0.25 eV. The maximum H binding energy for Si, Cr, Mn, Co and Mo is essentially zero, meaning they do not interact with H. (iv) The H-substitutional solute binding energies are roughly correlated with the solute atom's electronegativity and size. (v) The presence of a solute atom near a vacancy does not affect hydrogen binding to the vacancy provided the solute atom is not significantly larger than Fe.