Ab initio study of the modification of elastic properties of alpha-iron by hydrostatic strain and by hydrogen interstitials

TL;DR

This study uses ab initio calculations to analyze how hydrostatic strain and hydrogen interstitials affect the elastic properties of alpha-iron, revealing a linear decrease in elastic constants with increasing hydrogen content.

Contribution

It provides a detailed ab initio analysis of hydrogen and strain effects on alpha-iron's elastic properties, including quantitative insights into shear modulus reduction.

Findings

Elastic constants decrease linearly with hydrogen concentration.

Hydrogen causes approximately 1.6% shear modulus reduction per atomic percent.

Electronic effects oppose volumetric softening in elastic property changes.

Abstract

The effect of hydrostatic strain and of interstitial hydrogen on the elastic properties of $\alpha$-iron is investigated using \textit{ab initio} density-functional theory calculations. We find that the cubic elastic constants and the polycrystalline elastic moduli to a good approximation decrease linearly with increasing hydrogen concentration. This net strength reduction can be partitioned into a strengthening electronic effect which is overcome by a softening volumetric effect. The calculated hydrogen-dependent elastic constants are used to determine the polycrystalline elastic moduli and anisotropic elastic shear moduli. For the key slip planes in $\alpha$-iron, $[1\bar{1}0]$ and $[11\bar{2}]$, we find a shear modulus reduction of approximately 1.6% per at.% H.