Published October 26, 2023 | Version v1
Poster Open

Hydrogen Diffusion through Iron Surfaces

Description

The presence of hydrogen in a material as iron or steel severely impacts the material properties in a negative way and causes degradation and cracking due to hydrogen embrittlement.
While this is a well-established problem, most research has traditionally focused on explaining the microscopic effects of hydrogen in the bulk material. However, it is crucial to recognize that a major part of hydrogen enters the material in operando through its surface.
Despite the importance of the surface on hydrogen penetration, a systematic study examining the interplay between surface geometry and diffusion properties is still missing.
To bridge this gap, we conducted an extensive literature review and performed our own ab initio calculations on different surfaces of bcc-iron.
Therein, we found that different monocrystalline surface orientations can be assigned to one of three groups, which resemble the bonding characteristics of one of the low-index surfaces (100), (110), and (111). This is visible in the adsorption energies and adsorption site types and can be related to a proximity within the stereographic triangle, indicating a non-trivial relationship between surface geometry and bonding mechanism.
For the surface-to-subsurface diffusion, entry along the [100]-direction is easiest due to a stabilization of the first subsurface site splitting up the total diffusion barrier, while for the other surface orientations the diffusion barrier is way higher.
These insights help to understand the atomistic mechanisms related to the macroscopically observable hydrogen embrittlement, while giving hints on grain orientations that are capable to inhibit hydrogen penetration.

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