Microstructural evolution and performance of carbon fiber-toughened ZrB₂ ceramics with SiC or ZrSi₂ additive

ZrB₂–SiC/ZrSi₂ ceramics containing 30 vol% carbon fiber (C_f) additive were fabricated by hot pressing at low temperature (1500 ℃) using submicron ZrB₂ powders, and their microstructural evolution and performance were investigated. The addition of SiC or ZrSi₂ significantly reduced the onset sintering temperature and enhanced the densification of ZrB₂. ZrB₂–ZrSi₂–C_f showed poor performance owing to the serious fiber degradation, while the fiber degradation was effectively inhibited in ZrB₂–SiC–C_f resulting in high fracture toughness, substantial fiber pull-out, and non-brittle fracture mode for such material. The critical thermal shock temperature difference of ZrB₂–SiC–C_f was up to 741 ℃, significantly higher than those of ZrB₂–SiC/ZrSi₂ and ZrB₂–ZrSi₂–C_f. Moreover, this composite displayed a good oxidation resistance at 1500 ℃ in air.