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“Hydrogen gets into the metal and causes it to fracture unexpectedly in a process called hydrogen embrittlement,” said lead author Dr. John P. Hanson, who conducted the research as a PhD student at MIT. Scientists have studied hydrogen embrittlement for over 150 years, but it remains difficult to predict. “That’s largely because we don’t have a complete understanding of the mechanisms behind it,” explained Hanson.

In order to analyze the microscopic structure of a crack in a superalloy of nickel, the researchers employed two different synchrotron tools, high-energy diffraction microscopy and X-ray tomography, at the Argonne National Laboratory’s Advanced Photon Source, Illinois, U.S.

Metals are composed of microscopic crystals or grains. In nickel superalloys, the fractures brought on by hydrogen embrittlement travel along the boundaries between those grains. According to Hanson, the unique tools allowed scientists for the first time to look at not only the grain orientations around a crack in progress, but also the grain boundaries. From those observations, the team identified ten grain boundaries that are more resistant to cracks.

“We were able to show not only which grain boundaries are stronger, but exactly what it is about them that improves their performance,” concluded Hanson. This could ultimately allow engineers to build stronger metals by designing them with these characteristics.

The study, titled “Crystallographic character of grain boundaries resistant to hydrogen-assisted fracture in Ni-base alloy 725,” was published online in Nature Communications on Aug. 23, 2018. It was conducted in collaboration with Carnegie Mellon University, Pittsburgh, and Texas A&M University, College Station, U.S.

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