Role of grain boundary and dislocation loop in H blistering in W: A Density functional theory assessment

TL;DR

This study uses density functional theory to investigate how grain boundaries and dislocation loops in tungsten facilitate hydrogen blistering, revealing their roles as precursors and explaining blistering without void formation.

Contribution

First-principles analysis demonstrating the trapping of hydrogen at grain boundaries and dislocation loops in tungsten, elucidating their roles in hydrogen blistering mechanisms.

Findings

Grain boundary traps up to nine H atoms, weakening cohesion.

Dislocation loops can trap four H atoms, causing crystal breakage.

No H2 molecules form before tungsten bond fracture.

Abstract

We report a first-principles density functional theory study on the role of grain boundary and dislocation loop in H blistering in W. At low temperature, the {\Sugma}3(111) tilt grain boundary, when combined with a vacancy of vanishing formation energy, can trap up to nine H atoms per (1x1) unit in (111) plane. This amount of H weakens the cohesion across the boundary to an extent that a cleavage along the GB is already exothermic. At high temperature, this effect can be still significant. For an infinitely large dislocation loop in (100) plane, four H can be trapped per (1x1) unit even above room temperature, incurring a decohesion strong enough to break the crystal. Our numerical results demonstrate unambiguously the grain boundaries and dislocation loops can serve as precursors of H blistering. In addition, no H2 molecules can be formed in either environment before fracture of W bonds starts, well explaining the H blistering in the absence of voids during non-damaging irradiation.