Additive manufacturing technology, by manipulating and emulating inherent multiscale, multi-material, and multifunctional structures found in nature, has created new opportunities for constructing heterogeneous structures associated with special properties and achieving ultra-high mechanical performance and reliability in ceramic composite materials. In this study, we have developed an innovative fabrication method designated as coaxial 3D printing for the synchronous construction of two constituents into ceramic composites with a tooth enamel biomimetic microstructure. Herein, the stiff silicate and flexible epoxy served as a strengthening bridge and toughening layer, respectively. The method differed from the traditional approach of randomly dispersing reinforcing components within a ceramic matrix. It allowed for the direct creation of an internally effective three-dimensional reinforcement network structure in ceramic composites. This process facilitated synergistic deformation and simultaneous enhancement of multiple materials and hierarchical structures. Owing to the uniform distribution of internal stress and effective block of microcrack propagation, the biomimetically structured silicate/epoxy ceramic composite has demonstrated much significant enhancement in mechanical properties, including compressive strength (48.8±3.12 MPa), flexural strength (10.39±1.23 MPa), and flexural toughness (218.7±54.6 kJ/m³), which was 0.5, 2.1, and 47.5 times as high as those of the intrinsic brittle silicate ceramics, respectively. In-situ characterization and multiscale finite element simulation of microstructural evolution during three-point bending deformation further validated multiple-step features of the fracture process (silicate bridge fracture, interface detachment, epoxy extraction, and rupture), which benefited from interpenetrating structural features achieved by coaxial printing to accomplish with the complex propagating routines of the crack deflection in silicate ceramic composites. This coaxial 3D printing method paves the way for tailored toughening−strengthening designs for other brittle engineering ceramic materials.

High-entropy carbides are a nascent group of ceramics that are promising for high-temperature applications due to the combination of good stability, high hardness (H), high strength, and superior creep resistance that they display. Due to high melting points and low lattice diffusion coefficients, however, the high-entropy carbides are usually difficult to consolidate to a nearly full density. To cope with this challenge, herein, binary carbides including TiC, V₈C₇, NbC, Mo₂C, and WC with different carbon stoichiometry were used to prepare dense high-entropy (TiVNbMoW)C_4.375, and the influence of carbon vacancy on formation ability and mechanical properties of carbon-deficient high-entropy (TiVNbMoW)C_4.375 were investigated. Intriguingly, although the starting binary carbides have different crystal structures and carbon stoichiometry, the as-prepared high-entropy material showed a rock-salt structure with a relatively high density (98.1%) and good mechanical properties with hardness of 19.4±0.4 GPa and fracture toughness (K_IC) of 4.02 MPa·m^1/2. More importantly, the high-entropy (TiVNbMoW)C_4.375 exhibited low coefficient of friction (COF) at room temperature (RT) and 800 ℃. Wear rate (W) gradually increased with the temperature rising, which were attributed to the formation of low-hardness oxidation films at high temperatures to aggravate wear. At 800 ℃, lubricating films formed from sufficient oxidation products of V₂O₅ and MoO₃ effectively improved tribological behavior of the high-entropy (TiVNbMoW)C_4.375. Wear mechanisms were mainly abrasive wear resulting from grain pullout and brittle fracture as well as oxidation wear generated from high-temperature reactions. These results are useful as valuable guidance and reference to the synthesis of high-entropy ceramics (HECs) for sliding parts under high-temperature serving conditions.