The prospect of metal that can self-repair without any human intervention may seem like a plot from a science fiction story, but a team of scientists at Texas A&M University and Sandia National Laboratories have observed pieces of metal crack, then fuse back together without any human intervention, challenges and redefines basic scientific principles.
This opens up the exciting future possibility of self-repairing infrastructure, such as bridges, planes, and engines.
Sandia National Laboratories researcher Ryan Schoell using a specialized transmission electron microscope
(Image Credit: Craig Fritz, Sandia National Laboratories)
No concrete evidence until now
Although the concept of self-healing metals has been around for a while, there wasn't any concrete evidence supporting this idea until now. "This was absolutely stunning to watch first-hand," remarks Brad Boyce, a materials scientist at Sandia National Laboratories.
The focal point of the research is the self-repair capabilities of pure metals, which are metals unblended with others, like aluminium, copper, and lead. Boyce: "What we have confirmed is that metals have their own intrinsic, natural ability to heal themselves, at least in the case of fatigue damage at the nanoscale."
Boyce's team meticulously observed the process of crack formation and growth in a microscopic piece of platinum. To do this, they used a specialized electron microscope technique that pulled the ends of the metal 200 times per second.
To their astonishment, they noticed that after around forty minutes, the crack's end seemed to 'melt' away until the crack vanished completely, only to reappear later in a different direction.
While this self-healing phenomenon has only been observed at a tiny scale, Boyce notes that the beginnings of 'metal fatigue' also occur at a similar scale. Consequently, this discovery could revolutionize the construction industry.
The researchers caution that the observed self-repair happened in "nanocrystalline metals within a vacuum," which raises questions about whether other metals, especially those exposed to air, could display similar self-healing characteristics.
According to Boyce, the extent to which these findings are generalizable will likely become a subject of extensive research. The researchers don't know if this can also be induced in conventional metals in air.
In this artist's representation of the self-healing process in metals at the nanoscale, as discovered by Sandia National Laboratories, areas highlighted in green depict the location of a crack that surprisingly formed and then sealed itself. The red arrows serve as indicators, pointing to the direction of the unexpected pulling force that initiated this unique phenomenon.
(Image Credit: Dan Thompson, Sandia National Laboratories)
Theory already proposed in 2013
On this note, Michael Demkowicz, who proposed the theory of metal self-healing back in 2013, is optimistic. He hopes that this breakthrough will encourage researchers to consider that materials might behave in unexpected ways under the right circumstances.
The real-world implications of this discovery are potentially transformative, although much remains to be understood. The team is optimistic that this breakthrough could herald a technological revolution featuring longer-lasting, safer self-repairing engines, aircraft, and bridges. However, more research is needed before this vision can become a reality.
This groundbreaking research, a joint effort by Sandia National Laboratories and Texas A&M University, was published in the peer-reviewed scientific journal Nature. We have listed the publication below for those interested.
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