Mechanical and ablation properties of Cf/SiBCN-ZrB2 composites prepared by an in-situ reaction: Effect of carbon source

SiBCN ceramics were prepared by a novel inorganic method: the in situ reaction of amorphous SiBON and C. Differences in the mechanical and ablation properties of composites prepared from flake graphite and carbon black (denoted as Cf/CGZ and Cf/CBZ, respectively) were compared to find a suitable carbon source. The results showed that flake graphite is the optimal carbon source. The fracture toughness of the Cf/CGZ composite was 9.1 +/- 0.4 MPa & sdot;m1/2, which is 23.0% higher than that of the Cf/CBZ composite. This is because the flake graphite promoted crack deflection. Furthermore, after exposure to a plasma flame with a heat flux of 6.68 MW/m2 for 300 s, the mass and linear ablation rates of the Cf/CGZ composite are 0.39 mg/s and - 0.19 mu m/s, respectively, which is a decrease of 22.00% and 64.81%, respectively, as compared to those of the Cf/CBZ composite. This is because of the directional distribution of flake graphite, which improved the thermal conductivity, reduced the ablation surface temperature, and facilitated the formation of a dense ZrO2/SiO2 layer as an anti-ablation barrier.