Hydrogen Embrittlement of Aluminum: the Crucial Role of Vacancies

TL;DR

This paper uses first-principles calculations to show that vacancies and hydrogen impurities in aluminum can lead to embrittlement by forming vacancy clusters and microvoids, causing ductile rupture.

Contribution

It reveals that hydrogen can stabilize vacancy clusters in aluminum, promoting embrittlement, which is a novel insight into hydrogen-metal interactions.

Findings

Hydrogen stabilizes vacancy clusters in aluminum.

Vacancy clusters act as nuclei for microvoids and cracks.

Hydrogen trapping at vacancies facilitates ductile rupture.

Abstract

We report first-principles calculations which demonstrate that vacancies can combine with hydrogen impurities in bulk aluminum and play a crucial role in the embrittlement of this prototypical ductile solid. Our studies of hydrogen-induced vacancy superabundant formation and vacancy clusterization in aluminum lead to the conclusion that a large number of H atoms (up to twelve) can be trapped at a single vacancy, which over-compensates the energy cost to form the defect. In the presence of trapped H atoms, three nearest-neighbor single vacancies which normally would repel each other, aggregate to form a trivacancy on the slip plane of Al, acting as embryos for microvoids and cracks and resulting in ductile rupture along the these planes.