Ceramic metal composites like Narser provide excellent strength and the potential for mass production

Mollusks have a sturdy protective shell thanks to the internal knaker structure. A natural nanocomposite, Nacre exhibits excellent mechanical properties through both high strength and toughness. Therefore, Nacre is expected to be applied to fields such as lightweight structural composites and protective equipment. However, challenges such as limited material size, manufacturing efficiency and flexibility hamper development.

A research team led by scholar Yu Shuhong at the Chinese Academy of Sciences (CAS) at the University of Science and Technology (USTC) has reported a new strategy for preparing ceramic metal composites (ceramettes) like kar based on deformable alumina microspheres coated with nickel salts. This material has excellent bending strength and fracture toughness, and can be mass-produced in a variety of forms through simple techniques.

This study is published in the National Science Review.

First, the researchers synthesized adjustable alumina microspheres by emulsifying ceramic slurries in organic solvents. After sieving, they obtained microspheres of uniform particle size and coated them with a layer of nickel salt.

Additionally, modified composite microspheres were flattened to platelets through mold assembly and hot pressing. The metallic nickel layer formed a compartmentalized structure, accurately replicating the micro- “brick and mud” structure of the natural karker.

It is worth mentioning that by employing more microspheres and irregularly shaped molds, this strategy allows for all-in-one preparation of large irregularly shaped ceramettes.

Additionally, ceramettes like knakers are optimized at multiple scales. On the macroscale, the alumina ceramic layer alternates with the metallic nickel layer. On the microscale, nickel particles penetrate the ceramic layer to increase toughness, but the interface between the two phases is tightly connected.

This optimized material achieved a bending strength of 386 MPa at room temperature and maintained 286.86 MPa at high temperature 600°C. The toughness of the fracture reached 12.76 MPa·m¹/² (room temperature) and 12.99 MPa·m¹/² (high temperature).

The researchers found that when ceramics like karkers are exposed to force and failure, cracks deflect along the ceramic metal interface, preventing instantaneous failure due to energy dissipation. This makes it very suitable for applications in extreme environments, such as aerospace thermal protection and high-speed impact protection coatings.

This study further applies knaker-like structural designs to the field of ceramic metal composites, representing key steps in the practical application of biomimetic structural materials.