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 m1/2 was much higher than that of monolithic ZrB2 (2.3–3.5 MPa m1/2) and ZrB2–SiC ceramics (4.0–4.5 MPa m1/2). 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.