Ultra-high temperature ceramics (UHTCs), are defined as ceramic materials with melting point higher than 3000°C. Most of them are binary compounds where boron, carbon, or nitrogen combine with one of the early transition metals (Zr, Hf, Ti, Nb, Ta). This result in strong covalent bonds which are responsible for their high melting point, high hardness, good wear resistance and chemical stability. In addition, due to varying degrees of metallic bond character, they exhibit higher electrical and thermal conductivities than oxide ceramics. Such combination of properties allow ultra-high temperature ceramics to work in extreme conditions of high temperature, radiation levels, chemical reactivities or heat fluxes.
In particular, UHTCs are investigated for use in aerospace industry as hypersonic vehicles, scramjet propulsion and rocket components. Although, from such specific applications emerge also specific requirements. In hypersonic flight, one of the challenges is the bow shock at sharp leading edges, producing temperatures in excess of 2000°C, high heat fluxes, as well as highly reactive dissociated gas species. Due to high thermal conductivity, superior oxidation resistance and high strength at elevated temperatures, diboride ceramics (like ZrB2, HfB2, TiB2) are most often investigated for such applications among UHTCs. What limits it wider use though, is poor sinterability and moderate fracture toughness.
The aim of this work was to improve both thermal and mechanical properties of diboride ultra-high temperature ceramics, by preparing composites from TiB2/ZrB2-SiC/graphene systems. Materials were produced with the use of powder metallurgy and consolidated using the Spark Plasma Sintering technique. The essential properties (density, hardness, Young’s modulus, fracture toughness) of the composites were thoroughly investigated, and in depth analysis of microstructure was conducted. In addition, both thermal and electrical conductivities were measured. As summary, the influence of the SiC/graphene addition on various properties of TiB2/ZrB2 ultra-high temperature ceramics was presented.