Ultrafine 3D interpenetrated architecture of the cermet, where ceramic platelets are aligned and alternately arranged with metal matrix as in natural nacre (left). (Right) Comparison of the cermet’s mechanical properties with other materials.Materials that are simultaneously light, strong, tough, and able to damp vibrations and noise are challenging to produce because these properties tend to be mutually exclusive. Ceramics, for example, are hard and thermally stable but brittle. Metals, by comparison, are ductile and fracture resistant, but less hard. But now researchers have combined the best of ceramics (‘cer’) and metals (‘met’) in a new ‘cermet’ material [Liu et al., Materials Today (2022), https://doi.org/10.1016/j.mattod.2022.12.002].
Hybrid or composite cermets generally comprise a metal matrix reinforced by ceramic particles. One of the most well-known examples, tungsten-carbide cobalt composite, is widely used in cutting tools. But it can be difficult to construct complex architectures in cermets. Now Robert O. Ritchie of the University of California, Berkeley, and colleagues at the Institute of Metal Research, Chinese Academy of Sciences in Shenyang, the University of Science and Technology of China in Hefei, and ShanghaiTech University have created a new cermet inspired by the bricks-and-mortar structure of natural nacre, which makes up seashells like abalone.
“We developed a new cermet material… based on a fine modulation of constitution and architectures by taking lessons from Nature,” says Zengqian Liu, one of the authors of the study. “[It] exhibits an outstanding combination of properties which are hardly attainable in other materials.”
Unlike existing cermets, where a continuous phase metal matrix is combined with a discontinuous phase ceramic, the researchers fabricated a porous ceramic scaffold of Ti3AlC2 platelets aligned by vacuum filtration into which a molten Mg alloy is infiltrated. The MAX phase Ti3AlC2 ceramic platelets form a continuous layered interconnected structure, taking the role of the ‘bricks’ in the cermet. The porous scaffold also constrains crystal growth in the alloy as it solidifies, creating an ultrafine-grained structure.
“Both the ceramic and metal phases are continuous, mutually interpenetrated in 3D space, and arranged in an alternately layered fashion like natural nacre,” explains Liu.
The combination of an ultrafine-grained Mg alloy and ultrafine MAX ceramic platelets produces remarkable properties including high strength, good toughness, and damping capacity all at a low density. The cermet’s specific strength (strength-to-density ratio), at over 350 MPa/(g·cm-3 is higher than most bulk metals, ceramics, or composites of the two.
“The cermet material [is] appealing for structural load-bearing applications where lightweight materials are required for weight reduction and reducing vibrations at high stress levels,” points out Liu.
The researchers are now working on optimizing the bioinspired architecture to improve fracture toughness.