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Hydrogen embrittlement could lead to failure of fuel-cell cars

Fuel-cell cars may suffer from sudden failure of parts and components because of the little-known effect hydrogen can have on the metals used in vehicle engineering.

This is the concern of researchers at the Fraunhofer Institute for Mechanics of Materials in Freiburg, Germany, where specialist teams are studying a phenomena known as hydrogen-induced embrittlement.

Hydrogen is viewed as an eventual alternative to fossil fuels for transport, but the chemical element has an unusual way of making common vehicle metals such as steel, aluminium and magnesium brittle.

It has been shown that hydrogen can infiltrate metal lattice through corrosion or during chromium plating of car parts. This infiltration may also occur during welding, milling or pressing. The result is always the same: the material may tear or break without warning.

In a fuel-cell vehicle this could have detrimental effects on everything from the fuel tank and parts of the fuel cell to ordinary components such as ball bearings.

Nicholas Winzer, a researcher at the Fraunhofer Institute for Mechanics of Materials, said problems associated with hydrogen-induced embrittlement have been published since the early 1800s, but the issue still has no clear resolution. 

‘It’s not terribly well understood,’ he said. ‘It’s something that is very interesting for scientists because it’s complicated and quite challenging to figure out. It tends to be, for engineers, something that’s not really thought of until it becomes a problem.’

The Fraunhofer researchers are attempting to visualise, on an atomic scale, what happens to metal components when exposed to hydrogen. With this information, Winzer said that it could one day be possible to develop a software program that will help engineers design materials and components that mitigate hydrogen-induced embrittlement.

‘The easiest thing you can do is make sure the hydrogen doesn’t get into the material and you can do that by using different types of coatings that protect the material,’ he said. ‘But once the hydrogen is actually inside the material it can move around quickly and cause damage in different ways. The challenge is to stop the hydrogen from moving around.’

Winzer said that it could be theoretically possible to design ‘hydrogen traps’ in a material’s microstructure.

‘It could be some defect, it could be some little particle of impurity inside the material that causes that site to attract hydrogen and hold it,’ he said, adding that, while this could help slow material deterioration, there is no ‘cure all’ for hydrogen-induced embrittlement. 

Their experiments will mimic the experience components will undergo in a vehicle by combining the forces of temperature, mechanical stress and hydrogen. As metal samples are continuously heated up, the researchers will apply stresses to the material with special tensile test equipment that permits simultaneous mechanical loading and infiltration with hydrogen. The team will then determine the resistance of the material.

The researchers will use the results from the laboratory tests for computer simulation and calculate the hydrogen embrittlement in the metals. They will enlist Finite Element Method simulation to investigate the interaction between hydrogen and metal, both on an atomic and a macroscopic scale.

It is hoped that this will allow them to determine not only the most suitable materials for hydrogen, but also the best manufacturing process to create components.