A novel highly porous dual-phase high-entropy ultrahigh-temperature ceramic with outstanding properties

Ultra-high temperature ceramics (UHTCs) have a unique combination of high melting point, high strength, and high chemical stability, which makes them unique materials for a wide range of ultra-high temperature (>2000°C) applications. Herein we first report a novel highly porous dual-phase high-entropy UHTCs material composed of a high-entropy boride (HEB) phase and a high-entropy carbide (HEC) phase, which was fabricated by foam-gelcasting-freeze drying technology and high-temperature sintering with mixed borides and carbides as raw materials. The as-fabricated samples have uniform pore structure and firm skeleton that consists of random alternating distributions of HEB and HEC particles. The porous dual-phase high-entropy UHTCs samples embody ultra-high porosity of 90.1%–96.4%, low density of 0.31–0.87 g/cm³, high strength of 0.45–4.17 MPa and low thermal conductivity of 0.202–0.281 W/(m·K), as well as better oxidation resistance than single-phase HEC. The present results highlight the potential of as-prepared porous dual-phase high-entropy UHTCs as promising materials for ultra-high temperature thermal insulation applications.