Ultra High Temperature Ceramics : Densification, Properties and Thermal Stability.

Hypersonic flights, re-entry vehicles, and propulsion applications all require new materials that can perform in oxidizing or corrosive atmospheres at temperatures in excess of 2000°C and sometimes over the course of a long working life. Ultra High Temperature Ceramics (UHTCs) are good candidates to fulfill these requirements. Within this family, the ZrB2 and HfB2 based composites are the most attractive. The oxidation resistance of diboride-based compounds is better than that of SiC-based ceramics thanks to the formation of multi-oxide scales composed of a refractory oxide (skeleton) and a glass component. Onera is actively involved in several programs to develop such materials for both hypersonic civilian flights and for propulsion systems. In this paper, we present the ZrB2-SiC, ZrB2-SiC-TaSi2 and HfB2-SiC-TaSi2 composites developed in the Onera laboratories for leading edges or air intakes of future hypersonic civilian aircrafts flying up to Mach 6 (T~1100°C-1500°C) with comparisons with the state of the art. Then we discuss new perspectives for higher temperature applications (T>2000°C).