Stability of ultra-high temperature ZrB2-SiC ceramics under simulated atmospheric re-entry conditions

Microstructure modifications of an ultra-high temperature ZrB2–SiC ceramic exposed to ground simulated atmospheric re-entry conditions wereinvestigated and discussed. Fluid dynamic numerical calculations were carried out to correlate and explain the experimental results. The cross sectioning of the ceramic models after exposure (examined by SEM) showed a compact scale of zirconia (20 mm thick) underlying an external silica thin coating. A partially SiC-depleted region, a few microns thick, underneath the zirconia sub-scale was also seen. The post-test analyses confirmed the potential of the ZrB2–SiC composite to endure re-entry conditions with temperature approaching 2000 °C, thanks to the formation of a steady-state external multiphase oxide scale. Numerical calculations, which simulated the chemical non-equilibrium flow around the ceramic model, matched well the experimental results only assuming a very low catalytic surface behavior.