Researchers from University of Oxford and Brookhaven National Laboratory have uncovered how exposure to hydrogen atoms dynamically alters the internal structure of stainless steel. Their findings reveal that hydrogen allows internal defects in steel to move in ways not normally possible, which can lead to unexpected failure.
In a world-first experiment, the team used an advanced x-ray imaging technique to track how tiny defects inside stainless steel (called dislocations) respond to hydrogen exposure. This is crucial to understand how hydrogen can cause metals to weaken or fail, and could guide the design of next-generation alloys for a growing hydrogen economy.
Hydrogen has been touted as the ideal fuel for hard-to-decarbonize sectors, such as shipping, aviation, and heavy freight. However, hydrogen can cause unexpected cracking in metals (known as hydrogen embrittlement) which threatens the integrity of high-pressure vessels, pipelines, and critical components in energy systems.
While engineers have long known that hydrogen affects metal performance, the precise mechanisms at the atomic scale have remained elusive, as hydrogen is very difficult to detect.
Study principal investigator Prof. Felix Hofmann (Department of Engineering Science, University of Oxford) explained, “Using coherent x-ray diffraction, a nondestructive method, we were able to watch atomic-scale events unfold in real time inside solid metal without cutting open the sample. It has been tremendously exciting analyzing this data and piecing together the parts of this scientific puzzle. Some of the results really surprised us by showing behavior we weren’t expecting.”
To uncover what hydrogen does inside the material, the researchers used an ultra-bright beamline at the Advanced Photon Source in the U.S. to focus x-rays onto a single stainless-steel grain, roughly 700 nanometers in diameter. They then applied a technique called Bragg Coherent Diffraction Imaging to measure how the internal structure of this grain changed over time.
By imaging the steel grain over 12 hours, the experiment revealed three key changes after hydrogen was introduced: dislocations became unexpectedly mobile; a surprising out-of-plane motion of defects was observed; and the dislocation’s surrounding strain field reduced noticeably as hydrogen accumulated.
These findings help explain why hydrogen can lead to unexpected failure in metals, since it allows internal defects to move more easily and in ways that are not normally possible.
According to the researchers, the work directly informs how to model and predict material performance in hydrogen environments, feeding into multi-scale simulation frameworks used by industry. It also points toward potential strategies for engineering novel alloys that offer greater resistance to hydrogen embrittlement.
The study also involved researchers from Argonne National Laboratory and University College London. The team’s work was published in Advanced Materials.
Image – An artistic impression of the experiment: 3D rendering of the micro-scale stainless steel grain investigated in this study showing the evolution of defects inside it with time (early—blue lines, later—red lines). Courtesy of David Yang, Felix Hofmann (bubbles graphic sourced from Free PNG Logos, John D.).
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