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.
We have used density functional theory (DFT) to determine binding energies (BE’s) of carbon-vacancy (C-v) point-defect complexes of probable importance to C-based anelastic relaxation processes in fcc iron alloys. Calculations are presented for three types of stable point defect clusters: C-v pairs, di-C-v triplets, and tri-C-v quadruplets. We demonstrate semi-quantitative consistency of the calculated BE’s with internal friction results on Fe-36%Ni-C alloys. The BE’s, which are in the range-0.37 eV to-0.64 eV, were determined for a hypothetical non-magnetic (NM) fcc Fe. The effect of the magnetic state of fcc Fe on some of these quantities was investigated by DFT and is shown to be significant; the BE’s appear to be reduced in antiferromagnetic (AFM) fcc Fe.
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