Low-Temperature Processing of ZrB^sub 2^-ZrC Composites by Reactive Hot Pressing

Dense ZrB^sub 2^-ZrC and ZrB^sub 2^-ZrC^sub x-0.67^ composites have been produced by reactive hot pressing (RHP) of stoichiometric and nonstoichiometric mixtures of Zr and B^sub 4^C powders at 40 MPa and temperatures up to 1600 °C for 30 minutes. The role of Ni addition on reaction kinetics and densification of the composites has been studied. Composites of ~97 pct relative density (RD) have been produced with the stoichiometric mixture at 1600 °C, while the composite with ~99 pct RD has been obtained with excess Zr at 1200 °C, suggesting the formation of carbon deficient ZrC^sub x^ that significantly aids densification by plastic flow and vacancy diffusion mechanism. Stoichiometric and nonstoichiometric composites have a hardness of ~20 GPa. The grain sizes of ZrB^sub 2^ and ZrC^sub x-0.67^ are ~0.6 and 0.4 µm, respectively, which are finer than those reported in the literature. [PUBLICATION ABSTRACT]