Texas A&M scientists have discovered a new class of ceramics – MAX phases – that self-heal at room temperature.
According to the scientists, these engineered ceramics form natural faults or kink-bands during loading that can not only effectively stop cracks from growing, but also close and heal them, thereby preventing catastrophic failure.
“What’s really exciting about MAX phases is that they readily form kink-bands under loading which can self-heal cracks even at room temperature, making them suitable for a variety of advanced structural applications,” says corresponding author and assistant professor Ankit Srivastava.
“So far, self-healing of cracks in ceramics has only been achieved at very high-temperatures by oxidation and that is why self-healing of cracks at room-temperature by kink-band formation is remarkable.”
The scientists attribute this remarkable behavior of MAX phases to their atomically layered structures.
“Imagine a plain loaf of bread, it is homogeneous, so if I slice it up, each slice will look the same – similar in idea to conventional ceramics,” explains co-author and professor Miladin Radovic.
“But MAX phases are layered like a peanut butter sandwich with peanut butter between two slices of bread.”
For their experiments, the scientists used single crystal samples of chromium aluminum carbide MAX phase synthesized by Université Grenoble Alpes’s Thierry Ouisse.
These were then loaded inside an electron microscope using an in-house designed test fixture.
When viewed under an electron microscope while applying loading, the scientists observed that there were kink-band like defects that formed in the material, resembling those formed in natural rocks.
They further discovered that the material within kink-bands rotate during loading which not only form barrier against crack propagation but also eventually close and heal the cracks.
“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 lead author and doctoral student Hemant Rathod.
According to the scientists, MAX phases could help advance a host of next-generation technologies such as efficient jet engines, hypersonic flights, and safer nuclear reactors.
Image and content: Dharmesh Patel/Texas A&M Engineering