Thermo-chemical surface instabilities of SiC-ZrB2 ceramics in high enthalpy dissociated supersonic airflows

The response of SiC-ZrB2 ceramics at typical conditions of thermal protection systems of a re-entry spacecraft was studied. Evidences of the limits below which SiC-containing UHTC might play regarding the sharp leading edge technology for hypersonic flights were obtained. SiC-ZrB2 lab-scale proof demonstrators, shaped like a flat button (1 cm diameter) were manufactured and tested in non-equilibrium supersonic airflows up to 21 MJ/kg of specific total enthalpy and 3.5 MW/m2 cold wall heat flux, by using an arc-jet ground facility. The surface temperature of the demonstrator was determined coupling the recordings of an infrared thermo-camera (IR-TC) to those of a twocolor pyrometer (PYR). Under these severe aero-heating conditions, the UHTC articles endured rather well, though incipient thermo-chemical surface instabilities in the form of hot-spots started taking place. A sintered SiC ceramic was also tested under the same conditions for comparison. A numerical code implemented into a CFD package was used to interpret the observed phenomena. Potentials and limits of such a oxidation-resistant SiC-ZrB2 system to withstand such extreme conditions were finally outlined.