Improved densification and mechanical properties of high-entropy carbonitride ceramics via low-temperature powder synthesis and low-temperature sintering

High-entropy carbonitride ceramics usually require high-temperature sintering to achieve high density and phase purity, but this process often causes grain coarsening and reduces mechanical properties. In this work, (Ti,V,Ta,Nb,W)(C,N) powder (0.37 ± 0.09 μm) was synthesized at 1400℃ by carbothermal reduction-nitridation, and W 2 C, WC, and (Ti,Ta)O x byproducts were formed in situ. After sintering at 2100℃, a single-phase ceramic with 98.7% relative density was obtained, but the grain size increased to 10.39 ± 2.25 μm. In contrast, after sintering at 1500℃, the ceramic showed 98.8% relative density and a fine grain size of 1.09 ± 0.25 μm because the retained solid byproducts are located at grain boundaries, triple junctions, and pore-rich intergranular regions, where they may assist pore elimination. Although the ceramic sintered at 1500℃ was not single-phase, its hardness (20.49 ± 0.39 GPa) was higher than that of the 2100℃ sample (19.60 ± 0.32 GPa), mainly because of grain refinement and compositional partitioning between the core and rim. In addition, fracture toughness increased from 2.13 ± 0.30 MPa·m 1/2 at 2100℃ to 3.48 ± 0.23 MPa·m 1/2 at 1500℃ due to crack deflection by multiphase grain boundaries and heterogeneous interfaces. These results indicate that low-temperature powder synthesis combined with low-temperature sintering can effectively improve the mechanical properties of high-entropy carbonitride ceramics by retaining a fine-grained microstructure and using in situ formed byproducts.