Researchers Find Tiny Cracks in Metal Repairing Themselves

In a new experiment, scientists have observed metal pieces cracking and then fusing back together, all on their own, without any human help.

This new discovery has challenged fundamental scientific theories and could potentially lead to a major engineering revolution.

The research team from Sandia National Laboratories and Texas A&M University has shared their findings in the journal Nature.

Sandia materials scientist Brad Boyce described the observation as “absolutely stunning to watch firsthand.”

Boyce stated that they have confirmed the metals’ innate and natural capability to heal themselves, specifically when it comes to repairing fatigue damage at the nanoscale.

What is fatigue damage?

Materials that undergo repeated loading can develop cracks over time, a phenomenon known as fatigue, according to Wikipedia.

These fatigue cracks initiate at points of stress concentration and propagate with continued cyclic stress, often leaving characteristic patterns called striations on the fracture surface.

Fatigue damage is a major cause of machinery wearing out and eventually breaking down. When machines undergo repeated stress or motion, it leads to the formation of tiny cracks that are invisible to the naked eye.

As time passes, these cracks expand and propagate until, suddenly, the entire device breaks or fails.

The crack that Boyce and his team witnessed vanishing was one of these tiny yet significant fractures measured in nanometers.

Boyce pointed out that many structures, from solder joints in our electronic devices to vehicle engines and bridges we use, often fail unexpectedly. This is because of cyclic loading, which causes cracks to form and eventually leads to fractures.

When these structures fail, it results in costly replacements, lost time, and in some cases, injuries or even loss of life. The economic impact of these failures in the U.S. amounts to hundreds of billions of dollars every year.

Unexpected discovery of ‘self-healing’ metals

In 2013, Michael Demkowicz, who was then an assistant professor at the Massachusetts Institute of Technology’s Department of materials science and Engineering, began challenging traditional materials theory.

He introduced a new theory based on computer simulations, suggesting that under specific conditions, metals could weld cracks together that result from wear and tear.

The validation of his theory came unexpectedly true at the Center for Integrated Nanotechnologies, a Department of Energy user facility jointly operated by Sandia and Los Alamos national laboratories.

“We certainly weren’t looking for it,” remarked Boyce on the unexpected discovery.

During the experiment at Sandia, the work was led by Khalid Hattar, who is currently an associate professor at the University of Tennessee, Knoxville, and Chris Barr. Their primary intention was to examine the formation and spreading of cracks in a nanoscale piece of platinum.

To achieve this, they used a specialized electron microscope technique they had developed. The method involved repeatedly pulling on the ends of the metal at a remarkable rate of 200 times per second.

After 40 minutes, the damage that had initially occurred began to reverse itself. One end of the crack fused back together as if it was undoing its previous path, and there was no evidence of the previous injury. However, with time, the crack regrew in a different direction.