Porous high-entropy (Zr_0.25Hf_0.25Nb_0.25Ti_0.25)C with high strength and uniform pore structure fabricated by freeze-casting

Ultra-high temperature ceramics (UHTCs) are considered as promising thermal insulation materials applied in ultra-high temperature environments (> 2000 °C). However, the high thermal conductivity and high density limit their further development and application. Herein we adopt the strategies of introducing porous structure and high-entropy effect to solve the above problems. Thus porous high-entropy (Zr_0.25Hf_0.25Nb_0.25Ti_0.25)C ceramics were prepared. In order to obtain the uniform pore structure and high mechanical property, the camphene-based freeze-casting method was used in this study. The as-prepared porous samples exhibit high porosity of 92.01–73.57% and homogeneously interconnected pore structure with average pore size of 40.8–19.6 μm. Besides, this work realizes the aims of lightweight (0.65–2.15 g/cm³) and low thermal conductivity (0.29–1.53 W/(m·K)). More importantly, porous samples still have the merit of high compressive strength (0.38–29.02 MPa) due to the even microstructure. The results show that highly porous high-entropy (Zr_0.25Hf_0.25Nb_0.25Ti_0.25)C with good overall properties can be an excellent candidate material for ultra-high temperature thermal insulation.