Inhibiting Effect of Additives on Formation of ZrC Phase in ZrB2–BN Composites by Reactive Hot Pressing

The ZrB 2 –BN composite without ZrC impurity was prepared successfully using reactive hot pressing via carbothermal reduction of ZrO 2 with B 4 C, C, and BN powders. The influences of additives and sintering temperature on the phase and microstructure of composites were investigated. The formation reaction of ZrC was inhibited by decreasing the evaporation of intermediate product B 2 O 3 due to forming a SiO 2 –B 2 O 3 eutectic system with the addition of SiO 2 or SiO 2 – CaF 2 . In comparison, SiO 2 –CaF 2 exhibited better inhibition capacity of ZrC. ZrB 2 –BN composite without impure ZrC phase was achieved. In addition, the content of ZrO 2 decreased with increasing sintering temperature, and finally disappeared when sintered at 1800°C. Moreover, the relative density of the ZrB 2 –BN composite reached 96.9%.