Low-temperature facile and fast preparation of (Hf, Ta)B2-(Hf, Ta)C-SiC ultrahigh-temperature multi-phases ceramics: Microstructure and mechanical properties

Aiming at the high sintering temperature and densification difficulty in ultrahigh-temperature ceramics, the low-temperature facial and fast preparation of ultrahigh-temperature multi-phases (Hf, Ta)B 2 -(Hf, Ta)C-SiC solid solution ceramics was realized using in-situ reaction combined with hot pressing, where the HfSi 2 , TaSi 2 , B 4 C and C were used as raw materials. The effect of Hf/Ta molar ratio on the microstructural evolution and mechanical properties of ultrahigh-temperature multi-phases ceramics was investigated. The results found that the in-situ reaction and the formation of solid solution phase could promote the densification process. On the other hand, the addition of Ta element induced the formation of high aspect ratio grains with an interlock structure within the ceramic matrix and significantly improved the mechanical properties. When the Hf/Ta molar ratio was 7/3, the multi-phases ceramics exhibited the best mechanical properties, with a hardness of 25.59 GPa, a flexural strength of 556.61 MPa, and a fracture toughness of 5.13 MPa·m 1/2 . The enhanced mechanical properties were attributed to the synergistic effect of multiple strengthening and toughening mechanism, including grain bridging, crack bifurcation and grain pullout induced by high aspect ratio (Hf, Ta)B 2 grains.