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To enhance the oxidation resistance of carbon/carbon composites, here we designed and fabricated a novel β-Y2Si2O7 nanowire-toughened Y2SiO5/Y2O3-Al2O3-SiO2 coating by pulse arc discharge deposition with a later hot dipping process onto SiC coated carbon/carbon composites. Triple protection of the nanowire toughening, inlaid phases and compound Y2O3-Al2O3-SiO2 glass ceramic layer are contributed to the good oxidation resistance of this coating. After 50 thermal cycles between 1673 K and room temperature, the weight loss of coated samples was only 36.0 g·m−2, and the weight loss of the coated samples was only 31.7 g·m−2 in air at 1673 K for 176 h.

Ablation of C/C-ZrC composites was studied at a heat flux of ∼25 MW/m2 in a nitrogen plasma torch. C/C-ZrC composites with 4.1 wt% ZrC illustrate a lower linear ablation rate than other composites, that is, 44.7 % lower than that of C/C composites. The formed ZrN/ZrO2 may decrease the ablation rate of the composites by blocking the chemical reaction of the plasma jet and carbon and absorbing significant heat from the plasma jet by their melting and evaporation. The ablation of C/C-ZrC composites is controlled by thermochemical ablation, mechanical breakage, and carbon sublimation, which plays a minor role.

Three types of carbon/carbon composites containing ZrC particles (C/C-ZrC) were prepared by the carbothermal reduction reaction of ZrO2 and carbon. ZrC distributed around the carbon fibers, among the fibers, and dispersed in the carbon matrix corresponding to the ZrO2 layer, particles, and whiskers in the carbon fiber preforms, respectively. The composite with ZrC dispersed in the carbon matrix showed the best ablation resistance. Dispersive distribution of the ZrC particles was helpful to form a continuously melting ZrO2 layer and this can prevent carbon from oxidizing and restrain the mechanical erosion of the composites.

Effect of YC2 on the ablation behavior of C/C–ZrC composites was investigated in an oxyacetylene flame. The chemical reactions between the oxyacetylene flame and carbides were calculated based on the principle of minimum free energy. Lots of pits are formed on the surfaces of fibers and matrices, providing more active sites and accelerating the chemical ablation. Meanwhile, the formed pits reduce the strength of fibers and matrices, increasing the mechanical breakage rate. Ablation of C/C–ZrC composites after adding YC2 is controlled by both the chemical ablation and mechanical breakage, while ablation of C/C–ZrC composites mainly depends on the chemical ablation.

C/C-ZrC-SiC composites were fabricated by carbothermal reaction of hydrothermal co-deposited oxides and resulted in homogeneous microstructure. The fracture behavior passed from pseudo-plastic to brittle fracture with the increase in ZrC/SiC molar ratios. The composites with a molar ratio of ZrC/SiC≈2:1 presented outstanding ablation resistance with a mass ablation rate of 0.06 mg cm−2 s−1 and a linear ablation rate of 0.13 μm s−1. The optimal ZrC/SiC molar ratio provided a suitable balance of viscosity and flowability of the oxides scale, which not only possessed enough solid ZrO2 to endure the scouring but also had moderate liquid-phase to seal the defects and limited the oxidation.

To protect carbon/carbon (C/C) composites against oxidation, a Nb coating was prepared on C/C composites by a DC magnetron sputtering method. The phase composition, microstructure and oxidation behavior of the Nb coated C/C composites were investigated. The initial oxidation temperature of the Nb coated C/C composites is about 350 K higher than that of the as-received C/C composites. The Nb coating can protect the C/C composites from oxidation at 1173 K for 75 min. The failure of the coating is considered to arise from the cracks generated during the oxidation of the Nb coating.

To protect carbon/carbon (C/C) composites against oxidation, a MoSi2 outer coating was prepared on pack-cementation SiC coated C/C composites by a hydrothermal electrophoretic deposition. The phase composition, microstructure and oxidation resistance of the prepared MoSi2/SiC coatings were investigated. Results show that hydrothermal electrophoretic deposition is an effective route to achieve crack-free MoSi2 outer coatings. The MoSi2/SiC coating can protect C/C composites from oxidation at 1773 K for 346 h with a weight loss of 2.49 mg cm−2 and at 1903 K for 88 h with a weight loss of 5.68 mg cm−2.