Alumina/alumina ceramic matrix composites as part of the SHEFEX II thermal protection system

Kurzfassung

For DLR’s SHEFEX II (Sharp Edge Flight Experiment) campaign multiple TPS panels were fabricated from WHIPOX-type alumina/alumina ceramic matrix composites. These CMCs exhibit favourable properties such as high-temperature oxidation resistance and damage tolerance. A special feature of these CMCs is their inherent transparency for electromagnetic waves, making them attractive as thermal protection for antenna. Scheduled for autumn 2010 SHEFEX II will include an actively controlled atmosphere re-entry at a maximum cruise velocity of Mach 11 where a high thermal load on the TPS protected nose-cap is expected. However, emittance of alumina is low and consequently radiation cooling capability of alumina-based TPS panels is limited. In order to prevent thermal overload, emittance of CMCs is improved by superficial impregnation and coating with an oxidation-resistant “black” CoFe-spinel. Thermal performance and material stability was proofed in an arc-heated wind-tunnel at DLR. It turns out that CoFe-spinel surface modification can reduce CMC temperatures by more than 200 K in a Mach 6 hypersonic flow field. The modified CMC exhibits microstructural stability up to the expected TPS peak temperature of 1300°C. Design, manufacturing and set-up of the WHIPOX-TPS segments of SHEFEX II are presented.