Inhibiting Effect of Additives on Formation of ZrC Phase in ZrB_2-BN Composites by Reactive Hot Pressing

摘要

The ZrB_2-BN composite without ZrC impurity was prepared successfully using reactive hot pressing via carbothermal reduction of ZrO_2 with B_4C, C, and BN powders. The influences of additives and sintering temperature on the phase and micro-structure of composites were investigated. The formation reaction of ZrC was inhibited by decreasing the evaporation of intermediate product B_2O_3 due to forming a SiO_2-B_2O_3 eutec-tic 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℃. Moreover, the relative density of the ZrB_2-BN composite reached 96.9%.