Abstract: Compared to conventional ultra-high temperature ceramics (UHTCs), multi-principal carbonitride UHTCs exhibit superior high-temperature stability and ablation resistance. However, the inherent brittleness of these materials poses a significant constraint on their widespread applications. To overcome this drawback, in this study, (Ti,Zr,Hf,Ta,Cr)(C,N)-SiC ceramics were fabricated by combining mechanical alloying/nitridation with spark plasma sintering through the introduction of a second-phase SiC particles (SiC_p) into the system, and influence of different SiC_p contents on the mechanical properties and ablation resistance of the materials was systematically investigated. The results indicate that incorporation of SiC_p effectively enhances the mechanical properties of the materials. When the volume fraction of SiC_p reaches 20%, the fracture toughness achieves (5.18±0.24) MPa·m^1/2, representing a substantial enhancement of 31.5% compared to the (Ti,Zr,Hf,Ta,Cr)(C,N) ceramic. This improvement in fracture toughness can be attributed to toughening mechanisms including crack deflection and branching owing to the introduction of SiC_p. Further oxygen-acetylene ablation tests at 2100 ℃ for 120 s demonstrate that incorporation of SiC_p also significantly enhances the ablation resistance of the material. The optimal performance is achieved at a SiC_p volume fraction of 20%, with a mass ablation of -0.92 mg/s and a linear ablation of -1.17 μm/s, outperforming most reported conventional UHTCs. The enhancement in ablation resistance can be attributed to the pinning effect exerted by a high-melting-point multicomponent oxide skeleton on the low-melting-point SiO₂ phase, as well as the synergistic formation of a multicomponent dense oxide barrier that effectively suppresses oxygen diffusion. This work presents a strategy to resolve the intrinsic brittleness of multi-principal carbonitride UHTCs through the optimal incorporation of SiC_p, which concurrently improves the mechanical properties and ablation resistance. These results provide a theoretical foundation and experimental data for the design of advanced thermal protection materials.

Key words: multi-principal carbonitride ceramic, SiC particle, mechanical property, ablation resistance