An Ultra-High Temperature Ceramic with Improved Fracture Toughness and Oxidation Resistance

Hypersonic missile defense systems are being designed to reach global threats. During flight, external surfaces are predicted to reach temperatures in excess of 2200C. As a result, innovative, high performance thermal protection systems (TPS) are of great demand. Among ultra-high temperature ceramics (UHTC), it is well known that ZrB2- and HfB2-based materials have high melting temperatures and relatively good oxidation resistance. However, major obstacles, such as low fracture toughness, oxidation resistance at temperatures above 2000C, and lack of economical processing methods, will prohibit widespread employment of these UHTCs in future thermal protection systems. Plasma Processes proposes to address fracture toughness, oxidation and fabrication limitations of the ZrB2/SiC system. An investigation of lamellar microstructures observed in VPS ZrB2/SiC-based materials (and not hot pressed ZrB2/SiC) will be conducted. Avenues to improve fracture toughness by microstructure control of these phases will be identified. To improve oxidation resistance beyond 2000C, rare earth compounds will be added to in-situ form stable pyrochlore phases. Finally, the ability to apply ZrB2-SiC protective coatings to C/C and fabricate near-net-shape monolithic structures will be demonstrated. These efforts will demonstrate the economical fabrication of ZrB2 based materials, with improved toughness, and enhanced oxidation resistance at temperatures >2200C.