Threshold concentration for H blistering in defect free W

TL;DR

This study uses density functional theory to identify a threshold H concentration in defect-free tungsten that leads to spontaneous vacancy and interstitial formation, initiating blistering without H2 molecule formation.

Contribution

It provides a quantitative threshold for H concentration triggering blistering in tungsten, highlighting the role of lattice distortion and defect formation.

Findings

Exothermic vacancy and SIA formation occurs when H:W exceeds 1:2.

Spontaneous micro-void formation can accommodate H2 without H2 molecule formation.

Supersaturated H causes severe lattice distortion and increased H trapping.

Abstract

Lattice distortion induced by high concentration of H is believed to be precursor of H blistering in single crystalline W (SCW) during H isotope irradiation. However, the critical H concentration needed to trigger bond-breaking of metal atoms presents a challenge to measure. Using density functional theory, we have calculated the formation energy of a vacancy and a self-interstitial atom (SIA) in supersaturated defect-free SCW with various H concentrations. When the ratio of H:W exceeds 1:2, the formation of both vacancies and self-interstitials becomes exothermic, meaning that spontaneous formation of micro-voids which can accommodate molecular H2 will occur. Molecular H2 is not allowed to form, and it is not needed either at the very initial stage of H blistering in SCW. With supersaturated H, the free volume at the vacancy or SIA is greatly smeared out with severe lattice distortion and more H can be trapped than in the dilute H case.