Researchers take first 3D images of microscopic hydrogen-embrittled cracks in metal
20 September 2018
Microfractures in metal alloys, though impossible to see with the naked eye, can easily spread when exposed to water or hydrogen and lead to major problems in structures such as bridges, electrochemical and nuclear plants and hydrogen storage containers, leading to failures and expensive repairs.
In a recent study involving a Lawrence Livermore National Laboratory (LLNL) scientist, researchers at the Massachusetts Institute of Technology (MIT), Argonne National Laboratory and other institutions, have, for the first time, captured 3D images of microscopic cracks in metal caused by exposure to hydrogen, also known as hydrogen embrittlement. Using the images, researchers identified 10 orientations of microscopic structures called grain boundaries that can deflect cracks and prevent damage caused by hydrogen.
Using advanced synchrotron-based X-ray diffraction and tomography techniques, researchers were able to capture 3D images of microscopic cracks in nickel alloy caused by exposure to hydrogen, also known as hydrogen embrittlement. Credit: Dharmesh Patel/ Texas A&M University College of Engineering.
The open-access research, published in Nature Communications, relied on synchrotron-based X-ray diffraction and tomography techniques to investigate hydrogen-assisted cracks in nickel alloy. The result is a new method for analysis called 3D microstructure mapping that could aid materials processing methods aimed at blocking cracks from further propagation, strengthening metals and leading to longer lifespans for structures and components.
It’s been a long process. This was a new technique that complements electron backscatter diffraction but does it in 3D. When you’re thinking about how a crack propagates, it’s inherently a 3D problem. You need to have information about that crack, its morphology and how it’s related to the microstructure. There’s a lot of information involved.Jonathan Lind, LLNL
To perform the nondestructive analysis required for the project, researchers took samples of cracked nickel alloy to the Advanced Photon Source beamline at Argonne, illuminating them with high-energy x-ray beams, and using a camera to pick up diffracted and transmitted beams.
By testing hundreds of thousands of orientations, analyzing millions of points and matching the data with physical models, researchers were able to turn the diffraction spots into a 3D microstructure image. The image obtained from this complicated data showed which grain boundary types can deflect cracks, indicating that “boundaries with low index plains” or BLIPS, were especially resistant to damage.
The findings, researchers concluded, could pave the way to improved predictions of the mechanical behavior of hydrogen-embrittled metals. As metal alloys are engineered, stronger grain boundaries could be promoted while detrimental ones are processed out to create more obstacles for cracks and stop them from spreading. Engineers could design microstructures to extend the life of materials, potentially saving on costs of repairs or replacement of metal components regularly exposed to water or hydrogen.
When you have these fracture events, it inhibits the life cycle of materials. If you could process the microstructure with many more BLIPS, they could deflect cracks better or blunt them and you could potentially increase the life of the material significantly. In theory, that’s the idea behind grain boundary engineering.
—Jonathan Lind
The Department of Energy and National Science Foundation funded the research.
Resources
John P. Hanson, Akbar Bagri, Jonathan Lind, Peter Kenesei, Robert M. Suter, Silvija Gradečak & Michael J. Demkowicz (2018) “Crystallographic character of grain boundaries resistant to hydrogen-assisted fracture in Ni-base alloy 725” Nature Communications volume 9, Article number: 3386 doi: 10.1038/s41467-018-05549-y
This analysis suggests hydrogen related industries have been either ignoring or understating the difficulties and implications of metal vulnerability.
While Hydrogen embrittlement has been understood for many decades it is not clear how an expanded H energy industry expects to solve the problem.
Various designs are mentioned including shipping and handling solutions with such as plastics and coatings, 'New alloys' are discussed as if they exist for all applications but reading this article should give cause for clarification if not concern.
Obviously on site inspection will not be possible and quality control or predictive tools are only as good as the weakest link.
Failures are not an option . (Brooklyn's recent fires from gas pipes over pressurised are an example when the system breaks down) While the commonly referenced 10% H added to existing appliances and NG delivery pipelines is stated as proven, we know that any exposure including ageing in normal atmosphere can cause embrittlement.
It is definately a less well understood area that should concern the industry.
More explanation and certification seems appropriate.
Posted by: Arnold | 20 September 2018 at 03:40 PM
This is one of the reasons I favor reformers over high pressure hydrogen.
Posted by: SJC | 20 September 2018 at 10:22 PM
Here is an interesting take on hydrogen; a bit over the top; but, raises some points worth considering:
https://www.youtube.com/watch?v=xa6MGVmkvO8
Posted by: Lad | 21 September 2018 at 01:22 AM
That's the thing about straight talking, it often offends especially those worthy.
Posted by: Arnold | 21 September 2018 at 07:43 AM
Hydrogen is handled by the millions of tons annually, and has been in major use for a couple of centuries.
Sure, understanding and analysis are ever improving, but the notion that this is some sort of show stopper emerging out of nowhere to an industry fresh born to runFCEVs is absurd.
Posted by: Davemart | 21 September 2018 at 12:01 PM
Wiki gives a date for describing this affect as 1875 - or early days of 'industrial' scale metallurgy. At the same time as the describing the processes as today not well understood.
Posted by: Arnold | 21 September 2018 at 06:22 PM