Fabrication of multi-anionic high-entropy carbonitride ultra-high-temperature ceramics by a green and low-cost process with excellent mechanical properties

As a new category of ultra-high-temperature ceramics (UHTCs), multi-anionic high-entropy (HE) carbonitride UHTCs are expected to have better comprehensive performance than conventional UHTCs. However, how to realize the green and low-cost synthesis of high-quality multi-anionic HE carbonitride UHTC powders and prepare bulk ceramics with excellent mechanical properties still faces great challenges. In this work, a green, low-cost, and controllable preparation process of (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C_xN_1−x powders is achieved by sol–gel combined with the carbothermal reduction/nitridation method for the first time. The as-synthesized (Ti_0.2Zr_0.2Hf_0.2Nb_0.2Ta_0.2)C_xN_1−x powders possess high compositional uniformity and controllable particle size. In addition, the obtained bulk ceramics prepared at 1800 ℃ exhibit superior fracture toughness (K_IC) of 5.39± 0.16 MPa·m^1/2 and high nanohardness of 35.75±1.23 GPa, elastic modulus (E) of 566.70±8.68 GPa, and flexural strength of 487±41 MPa. This study provides a feasible strategy for preparing the high-performance HE carbonitride ceramics in a more environmentally friendly and economical manner.