Ultra-high temperature ceramics (UHTCs) are regarded as highly promising materials for aerospace applications due to their exceptional thermal and mechanical stability under harsh environmental conditions. In this study, to further enhance the performance of UHTCs across a broad temperature range, multiphase ceramics are fabricated through a combination of in-situ reaction and hot-pressing techniques, utilizing TaSi₂, ZrSi₂, B₄C, and C as raw materials. Subsequently, the microstructure, micromechanical properties, and oxidation resistance of the prepared ceramics are thoroughly investigated. The results reveal that the ZrB₂-TaB₂-SiC multiphase ceramic is formed at 1200 ℃. As the temperature increasing to 1500 ℃, the ZrB₂-TaB₂-SiC ceramic undergoes an in-situ solid-solution reaction, transforming into (Zr_0.5Ta_0.5)B₂-SiC. In terms of mechanical properties, the hardness values are 12.59 GPa for ZrB₂-TaB₂-SiC and 15.11 GPa for (Zr_0.5Ta_0.5)B₂-SiC, respectively. Similarly, the fracture toughness values are 3.66 MPa·m^1/2 for ZrB₂-TaB₂-SiC and 5.89 MPa·m^1/2 for (Zr_0.5Ta_0.5)B₂-SiC, respectively.　Thermogravimetric analysis demonstrates that the (Zr_0.5Ta_0.5)B₂-SiC solid-solution multiphase ceramics exhibit outstanding oxidation resistance. Specifically, the mass gain is only 0.48 mg/cm² when the temperature reaches up to 1600 ℃. The mechanism underlying this excellent oxidation resistance can be attributed to synergistic effect of multiphase oxides, which stabilizes oxidation film and reduces diffusion rate of oxygen.

Self-toughening ZrB₂-SiC based composites are fabricated by in-situ reactive hot pressing. The effect of sintering additive content on the microstructure and mechanical properties of the composites is investigated. Microstructure observation found that the in-situ reactive hot pressing could promote the anisotropic growth of ZrB₂ grains and the formation of interlocking microstructure. Such microstructure could improve the mechanical properties, especially, for the fracture toughness. The improved mechanical properties could be attributed to the self-toughening structure related to the ZrB₂ platelets and the formed interlocking microstructure, which could trigger various toughening mechanisms such as grain pull-out, crack bridging, crack deflection, and crack branching, providing the main contribution to the high fracture toughness.