High-entropy carbide ceramics (HECCs) are promising ultrahigh-temperature ceramics with exceptional properties, but their brittleness limits their practical application. Inspired by the structure of bamboo, fibrous monolithic high-entropy (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C-based ceramics (FMCs) with continuous weak cell boundaries were designed and fabricated through a combination of phase inversion and hot-pressing techniques. By optimizing the composition of the cell boundary, FM721 achieves a high fracture toughness of 8.3±1.5 MPa∙m^1/2, a 51.9% improvement over (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C (HECC), and a work of fracture of 784.0±190.8 J/m², a 1132.7% increase. The toughening mechanisms include crack deflection, crack branching, and load redistribution at the cell boundary, which increase the crack propagation path, consuming more energy. Moreover, the introduction of cell boundaries reduces the defect sensitivity and enhances damage tolerance. For example, FM721 maintains 77.8% of its initial flexural strength even after a 294 N indentation. Moreover, the relatively low density of FMCs and the thermal barrier effect at the cell boundaries significantly enhance the thermal insulation performance. As the temperature increases from room temperature (25 °C) to 1000 °C, the thermal conductivity of FM721 decreases by 22.9% and 34.5%, respectively, compared with that of the conventional HECC. This work presents a novel strategy for optimizing both the mechanical strength and thermal insulation performance of HECCs, providing insights for the design of thermal protection materials in extreme environments.

Si₃N₄ ceramics are promising wave-transparent materials with excellent mechanical and dielectric properties. Vat photopolymerization (VPP) three-dimensional (3D) printing provides a strategy for preparing ceramics with controllable complex structures. However, the difficulty in solidifying the slurry due to partial ultraviolet (UV) light absorption and the high refractive index of Si₃N₄ particles during the VPP process severely hinder the molding of Si₃N₄ ceramics. A higher laser power must be used to increase the curing depth, which generates large internal stresses and warps the samples. This study presents a method to solve the warpage problem during VPP-3D printing using tributyl citrate as a plasticizer. The plasticizer can weaken the force between polymer molecular chains and reduce the internal stress of the green body. Warpage decreases gradually with increasing tributyl citrate content, and the warpage decreases to 0% when the plasticizer content reaches 30 wt% at high laser powers from 600 to 750 mW. Samples with different layer thicknesses were printed, and the optimum thickness of 40 μm was obtained, at which the sintered Si₃N₄ samples possessed a unique combination of mechanical properties, including a bending strength of 338.29±12.08 MPa and a fracture toughness of 6.94±0.11 MPa·m^1/2 for the loading direction perpendicular to the build surface and 5.37±0.99 MPa·m^1/2 for the loading direction parallel to the build surface. The dielectric constant of all the samples is maintained in the range of 5.462–6.414. This work is expected to guide vat photopolymerization and the preparation of complex Si₃N₄ ceramic components.

Rare earth (RE) silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines. However, calcium–magnesium–alumina–silicate (CMAS) corrosion becomes much more serious and is the critical challenge for RE silicate with the increasing operating temperature. Therefore, it is quite urgent to clarify the mechanism of high-temperature CMAS-induced degradation of RE silicate at relatively high temperatures. Herein, the interaction between RE₂SiO₅ and CMAS up to 1500 ℃ was investigated by a novel high-temperature in-situ observation method. High temperature promotes the growth of the main reaction product (Ca₂RE₈(SiO₄)₆O₂) fast along the [001] direction, and the precipitation of short and horizontally distributed Ca₂RE₈(SiO₄)₆O₂ grains was accelerated during the cooling process. The increased temperature increases the solubility of RE elements, decreases the viscosity of CMAS, and thus elevates the corrosion reaction rate, making RE₂SiO₅ fast interaction with CMAS and less affected by RE element species.