How hydrogen causes metal fatigue

Hydrogen is known to speed up the breakdown of metals, particularly when cracks are developing in response to repeated cycles of stress and loading — a situation known as metal fatigue.

With hydrogen gas envisioned as a key energy source in the transition away from fossil fuels, it has become vital to understand how hydrogen can compromise the structural integrity of metals and what factors might speed up or slow down this process.

A study published in Science and Technology of Advanced Materials has shed new light on how environmental variables such as gas temperature and mechanical loading rate affect fatigue-induced cracking in the presence of hydrogen.

Osamu Takakuwa from Kyushu University and Yuhei Ogawa from the National Institute for Materials Science (NIMS) in Japan were particularly interested in what happens to hydrogen atoms that collect at the very tip of a metal crack and how they interact with the defects, such as dislocations, emitted from the tip to affect the speed of crack propagation.

“The rationales behind such a detrimental event need to be comprehensively studied to enable a fracture mechanics-based design to be safely applied to the engineering components used in hydrogenated environments,” Takakuwa says.

To do this, they carried out a series of experiments with low-carbon steel — which is widely used in car manufacturing, construction, and consumer goods — in a hydrogen-enriched environment. The steel was first fatigue-cracked at room temperature, then exposed to different temperatures and loading conditions. The researchers used a scanning electron microscope to track in precise detail how the tip of the crack changed under those different conditions.

This revealed that hydrogen atoms are less likely to be trapped at the tip of the crack at higher temperatures and are more free to move around, which relieves stress on the metal lattice and slows down the spread of the crack. Similarly, when the load frequency is lower, the crack spreads more slowly.

At lower temperatures, the opposite occurs. The surrounding metal is less plastic, and the hydrogen atoms are less free to move around and strongly trapped at the crack tip, which accelerates its propagation. These effects are also greater when there is a higher load frequency.

Their findings make it clear how important temperature is to the acceleration of fatigue cracks in metals exposed to hydrogen. Understanding these factors can inform better design and operation of metals in such environments.

Takakuwa says the next step is to obtain theoretical support for this experimental model by performing atomic-level analyses, such as molecular dynamics simulations,
to investigate the interactions between hydrogen and defects.

Read the paper 

Science and Technology of Advanced Materials: https://doi.org/10.1080/14686996.2024.2436345 

Further information

Prof Osamu Takakuwa 
[email protected] 
Kyushu University

STAM Inquiries 
[email protected] 
STAM Editorial Office 

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