Preparation, Mechanical Properties and Oxidation Behavior of (Ti0.25Zr0.25Nb0.25Ta0.25)C High-Entropy Ceramics

Abstract: In this work, (Ti_0.25Zr_0.25Nb_0.25Ta_0.25)C high entropy ceramics (HECs) was successfully prepared by spark plasma sintering (SPS) of carbide powder. The microstructure evolution, mechanical properties and oxidation behavior of HECs were systematically studied. The results show that the formation temperature of single-phase HECs is 1 800 ℃, which is below the reported HECs sintering temperature. The ceramic grains sintered at 1 900 ℃ are fine, average grain size is about 7.5 μm, and the element distribution is uniform, with a relative density of 99.2%. The room temperature microhardness of HECs sintered at 1 800 ℃ and 1 900 ℃ is 30.9 GPa and 33.2 GPa, respectively, and the fracture toughness is (4.6±0.24) MPa·m^1/2 and (4.5±0.31) MPa·m^1/2, respectively, higher than most reported HECs. The results of high-temperature nanoindentation test show that the hardness of HECs decreases with the increase of temperature. When the temperature reaches 500 ℃, the hardness of the ceramics sintered at 1 800 ℃ and 1 900 ℃ decreases to 21.9 GPa and 22.2 GPa, respectively, with outstanding high temperature stability. When the temperature is lower than 500 ℃, there is no obvious oxidation of HECs. When the temperature is higher than 650 ℃, there is obvious oxidation and the oxidation rate increases with the increase of temperature.

Key words: high entropy ceramics, (Ti_0.25Zr_0.25Nb_0.25Ta_0.25)C, high temperature mechanical property, spark plasma sintering, nanoindentation, oxidation behavior