2023-07-20 20:00:03
Scientists described this Wednesday (07.18.2023) how pieces of pure platinum and copper spontaneously heal cracks caused by metal by studying how cracks form and propagate in metal under stress. They expressed optimism that this ability might be incorporated into metals to create self-repairing machines and structures in the relatively near future.
Metal fatigue occurs when metal – including parts of machines, vehicles and structures – suffers microscopic cracks following being exposed to stress or repeated movement, damage that tends to worsen over time. Metal fatigue can cause catastrophic failure in areas such as aviation (jet engines, for example) and infrastructure (bridges and other structures).
Metal Refused: Healing “Cold Welding”
In experiments at Sandia National Laboratories in New Mexico, the researchers used a technique that pulled the ends of the tiny metal pieces regarding 200 times per second. At first a crack formed and spread. But 40 minutes into the experiment, the metal fused once more. The researchers called this healing “cold welding.”
“Cold welding is a well-known metallurgical process that occurs when two relatively smooth and clean metal surfaces are brought together to reform atomic bonds,” explains Brad Boyce, materials scientist at the Sandia National Laboratories, who collaborated in the direction of the study published in the magazine Nature.
Self-healing occurs at the nanometer scale
“Unlike the self-repairing robots in the ‘Terminator’ movie, this process is not visible on a human scale. It happens on a nanometer scale, and we haven’t been able to control the process yet,” Boyce added.
The metal pieces were regarding 40 nanometers thick and a few micrometers wide. Although healing was observed in the experiments only on platinum and copper, Boyce said the simulations indicated that self-healing can occur in other metals and that it is “entirely plausible” that alloys such as steel might exhibit this quality.
“It is possible to imagine materials adapted to take advantage of this behavior,” Boyce said.
Researcher Ryan Schoell of the US government’s Sandia National Laboratories in New Mexico uses a specialized transmission electron microscope technique developed by scientists Khalid Hattar, Dan Bufford and Chris Barr to study nanoscale fatigue cracks. Image: Craig Fritz/Sandia National Laboratories/REUTERS
“Given these new insights, there may be alternative materials design strategies or engineering approaches that might be devised to help mitigate fatigue failure.” In addition, these new insights may shed light on fatigue failure in existing structures, improving our ability to interpret and predict fatigue failure,” Boyce added.
The self-healing was observed in a very specific environment using a device called an electron microscope.
“One of the big questions the study leaves open is whether the process also occurs in air, not just in the vacuum environment of the microscope. But even if it only occurs in a vacuum, it has important ramifications for fatigue in spacecraft, or fatigue associated with subsurface cracks that are not exposed to the atmosphere,” Boyce said.
Metal self-healing prediction
Scientists have already created some self-healing materials, mostly plastics. Michael Demkowicz, co-author of the study and professor of Materials Science and Engineering at Texas A&M University, predicted the self-healing of metal a decade ago.
Demkowicz correctly thought that, under certain conditions, subjecting the metal to stresses that should normally make fatigue cracks worse might have the opposite effect.
“I now believe that tangible applications of our discoveries will take another 10 years to develop,” says Demkowicz.
FEW (Archyde.com, NatureSNL)
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