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.