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Analyzing the Ductility of Ceramics

Creating ductile ceramics is a challenging task. Plasticity in ceramics is scarcely observed and normally needs unique conditions like extreme temperatures to be plausible.

Erkka J. Frankberg is an Academy Postdoctoral Researcher at Materials Science and Environmental Engineering at Tampere University, Finland. Image Credit: Tampere University.

In the article, Dr. Erkka J. Frankberg, a Finland-based expert on the plasticity of ceramics, describes some of the new findings concerning room temperature plasticity in ceramics, stated by J. Zhang et al. in Science 378, 371 (2022).

In his commentary, Frankberg paints an extensive view of the possible advantages if such ductile ceramics could be made possible and scaled for commercial use, possibly creating a new stone age.

It would be significant to find ductile cermaics at room temperature due to atoms and the bonding between them. Ceramics consists of ionic and covalent bonding between atoms that considerably vary from, for instance, bonds in metal alloys.

One significant variation is that the ionic and covalent atom bonds are among the strongest known category. Consequently, ceramics must be among the most powerful engineering materials.

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

Erkka J. Frankberg, Expert, Plasticity of Ceramics, Tampere University

As an illustration of the potential of ductile ceramics, Zhang et al. display that if silicon nitride (Si3N4), a ceramic material, has been designed to display plasticity, it can exhibit an ultimate strength of approximately 11 GPa before fracture. This is nearly ten times stronger than some common grades of high-strength steel.

Higher strength means less material is needed to build moving machines such as vehicles and robots. Less material means lower inertia, meaning lower energy consumption and higher efficiency for all moving machinery. Higher wear and corrosion resistance of ceramics would allow higher up-time in these applications, which enables economic benefits.

Erkka J. Frankberg, Expert, Plasticity of Ceramics, Tampere University

Humanity has a constant requirement for ever-powerful engineering materials due to the vast cross-cutting effect it would have, thereby enhancing society's energy efficiency.

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

Erkka J. Frankberg, Expert, Plasticity of Ceramics, Tampere University

While the outcomes of Zhang et al. are spectacular illustrations of the potential of ductile ceramics, the outcomes are illustrated at the nanoscale, like the majority of similar outcomes in the field. A long road still remains to realize the objective of flexible ceramics, which requires that such outcomes are repeated in a bulkier material.

But every discovery of a new room temperature plasticity mechanism, such as that presented by Zhang et al., keeps us holding on to the dream of flexible ceramics.

Erkka J. Frankberg, Expert, Plasticity of Ceramics, Tampere University

Journal Reference

Frankberg, E. J., et al. (2022) A ceramic that bends instead of shattering. Science.


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