Development of Cf/C-UHTC composite and study of its resistance to oxidation and ablation in high-speed high-enthalpy air plasma flow

This article contains the results of research on the development of a C_f/C-UHTC carbon fabric composite based on a viscose precursor and a combined matrix consisting of partially sintered ceramics in a system consisting of HfC–HfB₂–NbC–NbB₂–TiC–TiB₂–B₄C–SiC, amorphous carbon, and pyrocarbon. The SiC fraction does not exceed 8.5–9.0 wt%. In its initial state, the composite has open porosity, with apparent and true densities of 18–22%, 2.25–2.29 g/cm³ and 2.79–2.91 g/cm³, respectively. The bending strength and the elasticity modulus are 27.8 ± 0.7 MPa and 7.8 ± 0.2 GPa, respectively, and the fracture strain is 0.85 ± 0.05%. The tests for resistance to oxidation and ablation were carried out in a gas dynamic flow regime and non-equilibrium air plasma heating at flow rates of 4.5–4.8 km/s and breaking enthalpy of 45–50 MJ/kg. Heating was performed in the temperature range T_w = 1400–2700 °C at the critical point on the front surface of the samples. The average linear ablation rate and mass loss rate of the composite are 6.3 ± 0.3 μm/s and 6.22 ± 0.44 mg/s. The estimated value of the conductivity factor is 0.280–0.285 W/(m K). The performance ability of the composite arises from the formation and evolution of a passivating heterogeneous oxide film consisting mainly of titanium niobate Ti₂Nb₁₀O₂₉, mixed solutions of Hf_1−xTi_xO₂, (Ti_1−xHf_x)_1−yNb_yO_z and (Ti_1−xHf_x)NbO₄ with broad homogeneity ranges, and also encapsulated carbide and boride particles. It is shown that the oxidation resistance of the composite increases as a result of the transition through a number of phases into a liquid state as the working temperature increases.