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

The response of three different SiC-ZrB2ceramics obtained by hot-pressing was studied at typical con-ditions of thermal protection systems of a re-entry spacecraft. Button-like lab-scale demonstrators weremanufactured and tested in high enthalpy dissociated supersonic airflows using an arc-jet ground facil-ity. Under severe aero-heating of up to 21 MJ/kg of specific total enthalpy and 3.5 MW/m2of (cold-wall)heat flux the SiC-ZrB2UHTC buttons endured rather well, though thermo-chemical surface instabilitiesstarted taking place for side wall surface temperatures of some buttons above 2050 K. The experimentaldeterminations of the surface temperature, correlated to the microstructure changes occurred duringtesting, allowed to interpret the observed phenomena. Potentials and limits of the oxidation-resistantSiC-ZrB2system to withstand such extreme conditions were outlined.