Oxidation of HfB2–SiC ceramics under static and dynamic conditions.

• Dense heterophase HfB 2 –SiC ceramics produced by hot pressing of SHS powders. • The best heat resistance was observed for the ceramics with 8 % SiC under gas-dynamic conditions. • A dense protective layer consisting of HfO 2 /HfSiO 4 grains is formed on the surface during oxidation. • Ceramics exhibits: heat capacity - 0.38 J/(g × K), thermal diffusivity - 40.9 mm2/s, and thermal conductivity - 89.7 W/(m × K). The kinetics and the mechanism of oxidation of ceramics based on HfB 2 and SiC, manufactured by elemental self-propagating high-temperature synthesis followed by hot pressing were investigated. The synthesis product contained HfC (x) and HfO 2 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 HfO 2 /HfSiO 4 grains formed on the surface of the ceramics during both oxidation conditions; the space between the grains was filled with amorphous SiO 2 –B 2 O 3. The best heat resistance was observed for the ceramics with 16 wt% SiC for static conditions and 8 wt% SiC for gas-dynamic conditions. [ABSTRACT FROM AUTHOR]