Hydrogen in $\alpha$ iron: modification of elastic properties and solubility in strain fields

TL;DR

This study uses ab initio calculations to show how hydrogen affects the elastic properties and solubility in alpha-iron, especially near dislocations, contributing to understanding hydrogen embrittlement.

Contribution

It provides a detailed theoretical analysis of hydrogen's impact on elastic moduli and solubility in alpha-iron, including effects near dislocation cores.

Findings

Hydrogen reduces elastic strength mainly through local volume expansion.

Hydrogen is strongly trapped by dislocations, increasing local concentration.

Strain fields influence hydrogen solubility and trapping near dislocations.

Abstract

The effect of interstitial hydrogen on the elastic properties of $\alpha$-iron is investigated using \textit{ab initio} density functional theory. We find that while the overall strength properties are reduced by H, the effects are mainly due to the resulting local volume expansion. We use these concentration-dependent elastic moduli to model the effects of homogeneous strain fields on H solubility and make extrapolations to H-solubility in the spatially-varying strain fields of realistic dislocations. We find that H is strongly trapped by dislocations of both the edge and screw variety, leading to a remarkable increase in the local H concentration near the dislocation cores. The strain dependence of the solution energy leading to accumulation of H near dislocation cores, as well as the reduction of elastic moduli which our calculations predict, is consistent with numerous experimental studies which indicate that the trapping of H near dislocations plays a significant role in the embrittlement of iron and steels.