The Hydrogen Cold Work Peak in BCC Iron: Revisited, with First Principles Calculations and Implications for Hydrogen Embrittlement

Ronald Gibala,William Arthur Counts,Christopher Wolverton

doi:10.1590/1980-5373-mr-2017-0868

Ronald Gibala, William Arthur Counts + Show 1 more

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https://doi.org/10.1590/1980-5373-mr-2017-0868

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Abstract

We examine experimental and theoretical results on the cold-work (Snoek-Koster) 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.

Highlights

The cold work peak, referred to as the SnoekKöster peak[1,2], in deformed bcc metals containing interstitial solutes has been studied for many decades
The first-principles calculations for H-point defect interactions (H-vacancy, H-solute, H-H) are described in detail elsewhere[20,21]. They are based on density functional theory (DFT) as implemented in the Vienna Ab-initio Simulation Package
The calculations employ spin polarization to account for the ferromagnetic state of bcc Fe

Summary

Introduction

The cold work peak (cwp), referred to as the SnoekKöster peak[1,2], in deformed bcc metals containing interstitial solutes has been studied for many decades. The types of dislocations involved in such experiments were not determined, but since most experimental work utilized room-temperature deformation[10], an assumption can be made that the binding energy corresponds to H-mixed dislocation interaction. Binding energies of this magnitude have been obtained in other types of studies such as permeation, thermal desorption spectroscopy, and similar kinetic or thermodynamic investigations[11]

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