Hydrogen Segregation at the Coherent α-Fe/V₄C₃ Interface: First-Principles Insights into the Role of Carbon Vacancies

Area of Science:

• Materials Science
• Physical Chemistry
• Computational Materials Science

Background:

• Hydrogen embrittlement poses a significant challenge to the durability of steels.
• Effective hydrogen trapping at interfaces is crucial for mitigating this issue.
• Vanadium carbide (V₄C₃) precipitates are known to influence hydrogen behavior in steels.

Purpose of the Study:

• To investigate hydrogen segregation and trapping mechanisms at the coherent α-Fe/V₄C₃ interface.
• To identify the most favorable sites for hydrogen interaction within the interface.
• To elucidate the role of carbon vacancies in hydrogen trapping at the atomic scale.

Main Methods:

• First-principles calculations were employed to simulate hydrogen behavior.
• Systematic examination of various hydrogen trapping sites, including interstitial, interfacial, and carbon-vacancy sites.
• Analysis of charge density, Bader charge, and density-of-states to understand bonding and stability.

Main Results:

• All investigated sites showed energetically favorable hydrogen trapping.
• Carbon vacancies within V₄C₃ exhibited the strongest hydrogen trapping tendency.
• Hydrogen atoms at carbon vacancies gained electrons, forming stronger bonds with vanadium atoms, thus increasing stability.
• H₂ molecules dissociated into atomic hydrogen within the vacancy, indicating atomic trapping is more stable.

Conclusions:

• Carbon vacancies play a critical role in regulating hydrogen trapping at the α-Fe/V₄C₃ interface.
• Atomic hydrogen trapping is more stable than molecular hydrogen trapping at these sites.
• The findings provide atomic-level insights into hydrogen trapping mechanisms relevant to vanadium carbide precipitates in steels.