The hydrogen cold work peak in BCC Iron: Revisited, with first principles calculations and implications for hydrogen embrittlement

Abstract

We examine experimental and theoretical results on the cold-work (Snoek-Köster) peak in bcc Fe due to H using density functional theory (DFT). We reaffirm that Seeger's interpretation of the H cold-work peak (Hcwp), involving motion of H with kinks on non-screw dislocations associated with the intrinsic-dislocation α peak, has experimental backing. Use of the solute-dragging theory of Schoeck suggests a H-mixed dislocation binding energy of 0.3 eV. The theory of Hirth, that the Hcwp involves H-screw dislocation interaction manifested as the temperature-reduced intrinsic-dislocation γ peak by the presence of H, has merit in that our DFT calculations disclose a similar magnitude, 0.2 eV, of H-screw dislocation binding. This result offers support for models of H-enhanced localized plasticity of H embrittlement. We also explore possible roles of H-vacancy binding, shown by DFT to be characterized by a binding energy of 0.6 eV, in H trapping and H embrittlement and lesser effects of H-solute binding involving small binding energies of ∼ 0.1 eV.