Mollusks possess sturdy protective shells, thanks to their internal nacre structure. Nacre, the natural nanocomposite, demonstrates outstanding mechanical properties through both high strength and high toughness, and is expected to be applied in fields such as lightweight structural composites and protective equipment. However, the practical applications of biomimetic structural ceramics are hindered by limited material size, fabrication efficiency and flexibility of being molded into various shapes.

In a study published in National Science Review, a research team led by Academician YU Shuhong from the University of Science and Technology of China (USTC) of the Chinese Academy of Sciences reported a new strategy for preparing the nacre-like ceramic-metal composites (ceramets) based on deformable alumina microspheres coated with nickel salt. These materials have excellent bending strength and fracture toughness, and can be mass-produced in various shapes through simple techniques.

Researchers synthesized size-tunable alumina microspheres through the emulsification of ceramic slurry in organic solvents. After sieving, they obtained microspheres of a uniform particle size, and coated them with a layer of nickel salt. Through mold assembly and hot-pressing, the modified composite microspheres were flattened into platelets. The metallic nickel layer formed a compartmentalized structure, precisely replicating the natural nacre's micro "brick and mud" structure.

It is worth mentioning that by employing more microspheres and irregular-shaped molds, this strategy allows the all-in-one preparation of large irregular-shape ceramets. Besides, the nacre-like ceramets had been optimized on multiple scales. On the macro scale, alumina ceramic layers alternate with metallic nickel layers. On the micro scale, nickel particles penetrate into the ceramic layer to enhance toughness, while the interface between the two phases is tightly bonded.

The optimized material achieved a flexural strength of 386 MPa at room temperature and still maintained 286.86 MPa at 600°C high temperature. Its fracture toughness even hit 12.76 MPa·m^¹/² (room temperature) and 12.99 MPa·m^¹/² (high temperature).

Researchers found that when nacre-like ceramets were subjected to force and fail, cracks would deflect along the ceramic-metal interface, preventing instantaneous failure through energy dissipation. This made them highly potential for applications in extreme environments.

This study applies the nacre-like structure design to the field of ceramic-metal composites, representing a step forward in practical applications of biomimetic structural materials.