Review of recent findings on room temperature plasticity in ceramics

Manufacturing ductile ceramics is a difficult task. Plasticity in ceramics is rarely observed and typically requires special conditions such as extreme temperatures to be achieved. Therefore, instead of denting, a typical ceramic coffee mug will shatter into pieces when dropped on a hard floor.

In his comment, Dr. Erkka J. Frankberg, an expert in ceramic plasticity, reviews some of the latest findings on room-temperature plasticity in ceramics, reported by J. Zhang et al. in Science. In his commentary, Frankberg takes a broader view of the potential benefits of such ductile ceramics if they become possible and scalable for commercial use, potentially ushering in a new Stone Age.

Why would it be important to develop ceramics that are ductile at room temperature? It is due to the individuals themselves and the bond between them. Ceramics have ionic and covalent bonds between atoms that differ significantly from (for example) bonds in metal alloys. One important difference is that ionic and covalent bonds of atoms are among the strongest known. As a result, in theory, ceramics should be among the strongest engineering materials available.

“The catch is this: while the bonds are strong, they also prevent atoms from moving easily through the material, and that movement is needed to create plasticity, or in other words, a permanent change in the perceived shape of the material. Without H plasticity, unfortunately, ceramics fracture well below their theoretical strength and in practice often have a lower ultimate strength than many metal alloys commonly used in engineering,” says Frankberg.

As a demonstration of the potential of ductile ceramics, Zhang et al. show that if silicon nitride (Si₃N₄), a ceramic material, engineered to exhibit ductility, can exhibit a massive ultimate strength of ~11 GPa before fracture. This is about 10 times stronger than some common grades of high strength steel.

What could super-strong ductile ceramics give us?

“Higher strength means less material is needed to build moving machines like vehicles and robots. Less material means lower inertia, which means lower energy consumption and higher performance for all moving machines. The higher wear and corrosion resistance of ceramics would allow longer uptime in these applications, which allows for financial benefits,” Frankberg points out.

Humanity has a constant need for ever stronger engineering materials because of the great cross-cutting impact it would have, improving society’s energy efficiency.

“Because of the softer bonding, there is a hard limit to how strong materials we can create from metals. To get to the next level of strength, ceramics are a good candidate,” Frankberg states.

While the results of Zhang et al. are a spectacular demonstration of the potential of ductile ceramics, the results are demonstrated at the nanoscale, like most similar results in the field. Therefore, a long and winding road still lies ahead to realize the dream of flexible ceramics, essentially requiring these results to be replicated in a bulkier material.

“But every discovery of a new room-temperature plasticity mechanism, like the one presented by Zhang et al., keeps us in the dream of flexible ceramics,” concludes Frankberg.

Provided by the University of Tampere