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.
