Fundamental Study of Hydrogen Segregation at Vacancy and Grain Boundary in Palladium

TL;DR

This study uses Density-Functional Theory to explore how hydrogen interacts with vacancies and grain boundaries in palladium, revealing mechanisms that could lead to hydrogen embrittlement and material failure.

Contribution

It provides a detailed atomic-level understanding of hydrogen segregation at vacancies and grain boundaries in palladium, highlighting implications for embrittlement mechanisms.

Findings

Hydrogen prefers octahedral interstitial sites in Pd.

Stable H-vacancy complexes can contain up to eight H atoms.

Hydrogen accumulation at grain boundaries causes boundary extension.

Abstract

We have studied the fundamental process of hydrogen binding at interstitial, vacancy and grain boundary (GB) in palladium crystals using Density-Functional Theory. It showed that hydrogen prefers to occupy the octahedral interstitial site in Pd matrix, however a stable H-vacancy complex with most H occupations would contain up to eight hydrogen atoms surrounding the vacancy at tetrahedral sites. Furthermore, H presence assists the pairing or formation of nearby vacancies, which in agreement with previous suggestions by both experiment and theory investigation. Also, this observation could imply about a hydrogen embrittlement (HE) mechanism through the connections of microvoid and cracks. The segregation of hydrogen at grain boundary, nevertheless, has shown a different effect. High H accumulation results in grain boundary extension, which is related the HE mechanism of grain decohesion observed by experiments.