Oxidation of HfB2–SiC ceramics under static and dynamic conditions

The kinetics and the mechanism of oxidation of ceramics based on HfB2 and SiC, manufactured by elemental self-propagating high-temperature synthesis followed by hot pressing were investigated. The synthesis product contained HfC(x) and HfO2 as impurity phases. Depending on the ratio between the main components, the samples were characterized by high structural and chemical homogeneity, porosity of 3–6 vol%, hardness up to 29 GPa, bending strength of 500–600 MPa, fracture toughness of 5.6–8.9 MPa × m1/2, and thermal conductivity of 86.0–89.7 W/(m × K). The oxidation was performed under static conditions at 1650 °C and upon exposure to a high-enthalpy gas flow. A dense layer consisting of HfO2/HfSiO4 grains formed on the surface of the ceramics during both oxidation conditions; the space between the grains was filled with amorphous SiO2–B2O3. The best heat resistance was observed for the ceramics with 16 wt% SiC for static conditions and 8 wt% SiC for gas-dynamic conditions.