Kinky class of ceramics self-heals cracks at room temperature
Ceramic materials are strong and can stand up to heat very well, but they’re notoriously fragile. Now, researchers at Texas A&M have uncovered a previously unknown self-healing mechanism in a certain type of ceramic, which works at room temperature.
When put under mechanical stress, ceramics are prone to cracking, which can quickly lead to complete failure as the material shatters. Some ceramics have been made to self-heal these cracks, but it usually requires chemical reactions that take place at very high temperatures.
For the new study, the researchers found that a particular type of ceramic, chromium aluminum carbide, could slow down crack propagation and even heal them, all at room temperature. That would make them far more useful in real-world applications.
These ceramics are known as MAX phases, and they’re made up of alternating layers of material. This structure is what gives them their healing ability, and the mechanism behind it is one that also plays out in geology. When a crack begins, defects called kink-bands form between the different layers. Crystals in the kink-bands rotate as the pressure is applied, which works to stop cracks from spreading any further. Better yet, these rotated crystals also actively heal the crack, so that once the force is relieved from the material, they’re almost undetectable.
“What’s really exciting is that this kinking or self-healing mechanism can occur over and over closing the newly formed cracks, thus delaying the failure of the material,” says Hemant Rathod, lead author of the study.
The researchers say that this kind of self-healing ceramic could be particularly useful for repairing cracks that form in materials subject to high-stress situations, such as jet engines, hypersonic craft, and nuclear reactors. And the effect might not be limited to MAX phases, but could apply to other materials with a similar layered structure.
The research was published in the journal Science Advances. An animation of the kink-band defects can be seen in the video below.
Source: Texas A&M University