ZrB2-based Ultra High Temperature Ceramics (UHTCs) by Arc Melting Process

Abstract

Interest in ZrB2-based ultra high temperature ceramics (UHTCs) has increased significantly in recent years because of thermal protection systems for hypersonic aerospace vehicles and reusable atmospheric re-entry vehicles. Because of its strong covalent bonding and its low self-diffusion coefficient, ZrB2-based ceramics have typically been densified at high temperature (> 1900 oC). A melt-solidification process, however, is another simple route for developing high performance materials. We have prepared several eutectic boride-carbide composites by arc melting process. Arc melted ZrB2-SiC composite showed round ZrB2 boride and lamellar structure with ZrB2 and SiC which is different from conventional microstructure of ZrB2-SiC. Moreover, the elongated mixed boride phase with lamellar structure was observed by addition of HfB2 and TaB2.The lamellar structures were advantageous for oxidation resistance at 1500 oC especially low oxygen partial pressure. In this study, the effect of microstructure and interconnectivity of SiC on the mechanical properties and oxidation behavior will be discussed and compared with conventional particulate transition metal borides-SiC composites. The mechanisms of the structure evolution during oxidation in oxyacetylene flame were also analyzed.