Microstructure, mechanical properties and thermal shock resistance of zirconium diboride containing silicon carbide ceramic toughened by carbon black

ZrB₂-20 vol.%SiC ultrahigh temperature ceramic containing 5 vol.% carbon black of nanometer size (ZSC) was prepared by hot-pressing at 1900 °C. The effect of carbon black addition on the microstructure and mechanical properties was investigated. Compared to the ZrB₂-SiC ceramics, the fracture toughness was significantly improved whereas flexural strength and hardness of the ZSC ceramic were slightly degraded. The fracture toughness as high as 6.6 ± 0.5 MPa m^1/2 was much higher than that of monolithic ZrB₂ (2.3-3.5 MPa m^1/2) and ZrB₂-SiC ceramics (4.0-4.5 MPa m^1/2). The toughening mechanisms were the crack deflection, bridging and branching. Furthermore, the effect of carbon black addition on the thermal shock resistance was systematically investigated and discussed.