Synthesis, Microstructure and Properties of Non-Stoichiometric High-Entropy Carbide (Nb0.2Ta0.2Ti0.2W0.2Zr0.2)Cx Powder

Non-stoichiometric high-entropy carbides (Nb0.2Ta0.2Ti0.2W0.2Zr0.2)Cx (x = 0.71–0.85) nanoscale powders were prepared using oxides and carbon as raw materials via carbothermal reduction. The (Nb0.2Ta0.2Ti0.2W0.2Zr0.2)C0.73 synthesized at 1700 °C exhibited a grain size of approximately 400 nm, an oxygen content of 0.3 wt.%, and uniform nanoscale distribution of the five metal elements. After ball milling, (Nb0.2Ta0.2Ti0.2W0.2Zr0.2)C0.73 powder was sintered by spark plasma sintering to produce high-entropy ceramics with a relative density of 98.1% and an average particle size of about 5.3 μm. The Vickers hardness, nano-hardness, Young’s modulus, and fracture toughness were 17.6 GPa, 29.1 GPa, 514 GPa, and 5.3 MPa·m1/2, respectively. The thermal conductivity of the ceramic at room-temperature was as low as 8.5 W/m·K.