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ZrB 2 has a melting point of 3245 o C and a relatively low density of 6.1 g/cm 3 , which makes this a candidate for application to ultrahigh temperature environments over 2000 o C. Beside these properties, ZrB 2 is known to have excellent resistance to thermal shock and oxidation compared with other non-oxide engineering ceramics. In order to enhance such oxidation resistance, SiC was frequently added to ZrB 2 -based systems. Due to nonsinterability of ZrB 2 -based ceramics, research on the sintering aids such as B 4 C or MoSi 2 becomes popular recently. In this study, densification and high-temperature properties of ZrB 2 -SiC ceramics especially with B 4 C are investigated. ZrB 2 -20 vol% SiC system was selected as a basic composition and B 4 C or C was added to this system in some extents. Mixed powders were sintered using hot pressing (HP). With sintered bodies, densification behavior and high-temperature (up to 1400 o C) properties such as flexural strength, hardness, and so on were examined.

This paper reports the microstructure of hot-pressed ZrB 2 -SiC ceramics with added B 4 C as characterized by transmission electron microscopy. ZrB 2 has a melting point of 3245 o C, a relatively low density of 6.1 g/cm 3 , and specific mechanical properties at an elevated temperature, making it a candidate for application to environments with ultra-high temperatures which exceed 2000 o C. Due to the non-sinterability of ZrB 2 -based ceramics, research on sintering aids such as B 4 C or MoSi 2 has become prominent recently. From TEM investigations, an amorphous layer with contaminant oxide is observed in the vicinity of B 4 C grains remaining in hot-pressed ZrB 2 -SiC ceramics with B 4 C as an additive. The effect of a B 4 C addition on the microstructure of this system is also discussed.