Scientists have discovered metals that appear to possess the ability to heal themselves. This has come about through an observation whereby microscopic cracks seem to vanish in experiments. The potential of the discovery could one day herald the enticing possibility of self-healing machines; something useful for engines, bridges and airplanes in terms of reversing the damage caused by wear and tear and heling to make structures both safer and longer lasting.
Sandia National Laboratories scientists witnessed pieces of metal crack, then fuse back together without any human intervention. This observation contradicts fundamental scientific theories.
According to Sandia materials scientist Brad Boyce: “This was absolutely stunning to watch first-hand. 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”.
Fatigue damage is one way machines wear out and eventually break. Repeated stress or motion causes microscopic cracks to form. Over time, these cracks grow and spread until the entire device breaks. The fissure observed as disappearing was a similar tiny but potentially consequential fracture.
Scientists have created some self-healing materials, mostly plastics; however, the concept of a self-healing metal has hitherto never been approached.
Professor Michael Demkowicz had previously theorized based that under certain conditions metal should be able to weld shut cracks formed by wear and tear. This was based on computational studies into the fundamental physics of material behaviour.
The metal was a piece of platinum being studied using a specialized electron microscope technique where researchers repeatedly pull on the ends of the metal 200 times per second. About 40 minutes into the experiment, the damage reversed course. Here, one end of the crack fused back together as if it was retracing its steps, leaving no trace of the former injury.
There is much still to learn about the self-healing process, including whether it will become a practical tool in a manufacturing setting. The research was conducted on nanocrystalline metals in vacuum. It is unknown whether the same effect can be induced in conventional metals in air.
It is hoped the discovery encourages materials researchers to consider that, under the right circumstances, materials can do things previously unexpected.
The research appears in the journal Nature, titled “Autonomous healing of fatigue cracks via cold welding.”
