Scalable and shapable nacre-like ceramic-metal composites based on deformable microspheres

Natural nacre that consists of brittle minerals and weak organics exhibits a high fracture toughness while retaining a high strength. The exceptional mechanical performance of nacre is attributed to its hierarchical structure like a 'brick-and-mortar' structure, which has inspired the development of tough ceramic-based composites. However, the practical applications of biomimetic structural ceramics are hindered by limited material size, fabrication efficiency and flexibility of being molded into various shapes. We herein report the fabrication of nacre-like ceramic-metal composites based on deformable alumina microspheres coated with nickel salt. Green bodies are produced by assembling the composite microspheres in molds with different shapes. During the hot-pressing sintering of the green bodies, the microspheres are flattened into platelets under pressure and fill up the entire space without visible voids. The aligned platelets are separated by nickel that is reduced from the nickel salt on their surface, constituting a typical 'brick-and-mortar' structure. By tuning the microsphere sizes, the microstructures of the composites can be optimized to obtain a high flexural strength (386 MPa at room temperature and 286.86 MPa at 600°C) and a high fracture toughness (12.76 MPa·m^1/2 at room temperature and 12.99 MPa·m^1/2 at 600°C) simultaneously. This strategy opens a promising avenue for the feasible mass production and all-in-one molding of nacre-like ceramic-metal composites with various shapes, sizes and raw materials.