A Cracked Piece of Metal Healed Itself in an Experiment That Stunned Scientists

Put this in the category of 'That's not meant to happen!': Scientists witnessed a metal repairing itself, which had never been seen before. If this process can be completely comprehended and managed, we may be on the verge of a new era in engineering.

A team from Sandia National Laboratories and Texas A&M University was evaluating the metal's resistance by pulling the ends of the metal 200 times per second using a specialized transmission electron microscope method. They then witnessed self-healing at ultra-small scales in a piece of platinum 40 nanometers thick hanging in a vacuum.

Cracks created by the above-mentioned strain are known as fatigue damage: continual stress and motion that creates tiny cracks, eventually leading machines or structures to fail. Surprisingly, after about 40 minutes of observation, the platinum fracture began to fuse back together and heal itself before beginning again in a new direction.

"This was absolutely stunning to witness firsthand," says Sandia National Laboratories materials scientist Brad Boyce. "We certainly weren't looking for it."

"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."

These are exact conditions, and we don't yet know how they are occurring or how we might exploit them. However, when you consider the expenses and labor necessary to repair anything from bridges to engines to phones, it's hard to say how much of a difference self-healing metals may make.

And, while the insight is novel, it is not entirely unexpected. Michael Demkowicz, a materials scientist at Texas A&M University, published a research in 2013 indicating that this type of nanocrack healing may occur due to the tiny crystalline grains inside metals basically altering their boundaries in reaction to stress.

Demkowicz also contributed to this current study, utilizing updated computer models to demonstrate that his decade-old beliefs concerning metal's self-healing behavior at the nanoscale were correct.

Another encouraging element of the research is that the automated repairing procedure occurred at room temperature. Metal typically takes a lot of heat to change its shape, but the experiment was conducted in a vacuum; it has to be seen whether the same process would occur in normal metals in a regular atmosphere.

A probable explanation is a process known as cold welding, which happens at room temperature when metal surfaces come close enough together for their atoms to tangle. Thin layers of air or pollutants often obstruct the process; in conditions such as space, pure metals can be pressed close enough together to actually attach.

"My hope is that this finding will encourage materials researchers to consider that, under the right circumstances, materials can do things we never expected," Demkowicz adds.

The research has been published in Nature.