On Wednesday (07.18.2023) scientists described how pieces of pure platinum and copper spontaneously heal cracks caused by the metal by studying how cracks form and propagate in the metal under pressure. They expressed optimism that this ability could be incorporated into metals to create self-repairing machines and structures in the relatively near future.
Metal stress occurs when metal—including parts of machinery, vehicles, and structures—suffers microscopic cracks after being subjected to repetitive stress or motion, 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 Rejection: Healing “Cold Welding”
In experiments conducted at Sandia National Laboratories in New Mexico, the researchers used a technique that pulled the tips of the tiny metal pieces about 200 times per second. At first a crack formed and spread. But 40 minutes into the experiment, the metal fused again. The researchers called this healing “cold welding.”
Brad Boyce, Materials Scientist at sandia national laboratories, who collaborated in the direction of the study Published in the journal nature.
Self-healing occurs on the nanometer scale
Boyce added, “Unlike the self-repairing robots in ‘Terminator,’ 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.”
The metal pieces were about 40 nanometers thick and a few micrometers wide. Although healing was only observed in experiments with platinum and copper, Boyce said the simulation indicated that self-healing could occur in other metals and that it was “quite plausible” for alloys such as steel to exhibit this quality.
“It is possible to imagine materials adapted to take advantage of this behavior,” Boyce said.
“Given these new insights, there may be alternative materials design strategies or engineering approaches that can be put in place 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.”
Self-healing is observed in a very specific environment using a device called an electron microscope.
“One of the big questions the study left open is whether the process also occurs in air, not just in the microscopic vacuum environment. But even if it only occurs in a vacuum, it has important implications for fatigue in spacecraft, or fatigue associated with subsurface cracks that are not exposed to the atmosphere,” Boyce said.
Predictor of self-healing for minerals
Scientists have already created some self-healing materials, most of them plastic. Michael Dimkovic, co-author of the study and professor of materials science and engineering at Texas A&M University, predicted metals’ self-healing a decade ago.
Dimkovic correctly believed that under certain conditions, subjecting the metal to stresses that would make fatigue cracks worse might have the opposite effect.
“I now think that concrete applications of our discoveries will take another 10 years to develop,” Dimkovic says.
FEW (Reuters, natureSNL)
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