Abstract: ZrB₂-SiC and C_sf/ZrB₂-SiC, two kinds of ultra-high temperature ceramic composites were fabricated by hot-pressing. The ablation behavior of them was studied by oxyacetylene torch test at a heat flux of 4186.8kW/m2 for 180s. For ZrB2-SiC, the surface temperature increases to 2406℃ during torch test and the average mass loss is -0.14%, linear ablation rate is
-1×10^-3mm/s. For C_sf/ZrB₂-SiC, the maximum surface temperature is 1883℃, and the average mass loss is -0.19%, linear ablation rate is -4×10^-4mm/s. From the surface and cross section analysis it is found that loosen ZrO₂ oxidation layer, SiC rich layer and unaltered layer form from outer layer to inner layer in ablated ZrB₂-SiC microstructure, where SiC rich layer has oxidation resistance. For C_sf/ZrB₂-SiC, ZrO₂-SiO₂ oxidation layer, SiC depletion layer and unaltered layer distribute from outer layer to inner layer, where the SiO₂ filled ZrO₂ oxidation layer formed in the surface can prevent
oxygen effectively.

Key words: ZrB₂-SiC, C_sf /ZrB₂-SiC, ultra-high temperature ceramic composites, ablation mechanism