Insights into Hydrogen Diffusion Characteristics and Interactions with Vacancy in Fe Crystal Lattices from...

Area of Science:

• Materials Science
• Computational Materials Science
• Physical Chemistry

Background:

• Hydrogen embrittlement significantly degrades material properties, driven by hydrogen atom diffusion within metal lattices.
• Understanding hydrogen diffusion mechanisms is crucial for predicting and mitigating embrittlement in iron alloys.

Purpose of the Study:

• To systematically investigate hydrogen diffusion in perfect and vacancy-containing α-Fe, γ-Fe, and ε-Fe crystal structures using first-principles calculations.
• To elucidate the influence of crystal structure and vacancy defects on hydrogen diffusion pathways, site occupancy, and aggregation behavior.

Main Methods:

• First-principles calculations were employed to determine hydrogen dissolution energies, interstitial site preferences, and diffusion pathways.
• Arrhenius equation was used to calculate hydrogen diffusion coefficients for different iron phases.
• Analysis of interatomic distance and interaction energy explored hydrogen aggregation and bubble nucleation.

Main Results:

• Hydrogen atoms preferentially occupy tetrahedral sites in α-Fe and octahedral sites in γ-Fe and ε-Fe.
• Diffusion coefficients followed the order α-Fe > γ-Fe > ε-Fe.
• Vacancy defects significantly alter diffusion pathways, increase hydrogen attraction, and facilitate bubble nucleation, requiring higher energy barriers for hydrogen to escape trapping.

Conclusions:

• The study clarifies hydrogen diffusion mechanisms in different iron phases and highlights the critical role of vacancies in accelerating hydrogen embrittlement.
• Findings provide fundamental insights for designing hydrogen-resistant materials and developing strategies to prevent embrittlement.