High Temperature Oxidation Resistance Performances Of ZrB₂-SiC Coatings On Carbon/Carbon Composites By Plasma Spraying Deposition

Carbon/Carbon（C/C） composites are widely used as thermal structure materials in aerospace field, owing to their excellent properties, such as low density, low thermal expansion coefficient, high specific strength and modulus of elasticity, good thermal shock resisitance, etc. However, when the service temperature of C/C parts exceeds 400 ℃, it will be oxidized severely. Applying the anti-oxidation coating on the surface of C/C composites is an effective method to improve the oxidation and ablation resistance of C/C composites.ZrB₂-SiC ceramics exhibit good anti-oxidation property at high temperature, the SiO2 and B2O3 obtained from oxidation of ZrB₂-SiC can provide the material a “self-healing” property at high temperature, it is a promising material for the anti-oxidation coating. Plasma spraying is a highly efficient coating-deposition method, it is suitable for the ceramic coating deposition for the temperature of plasma arc is above 10000 ℃, the without high-temperature deposition processing will not damage the C/C substrate.In this paper, the agglomerated ZrB₂-SiC composite powders are produced by the method of spray drying. After that, ZrB₂-SiC composite coatings are deposited on C/C substrate by atmospheric plasma spraying. The micro structure and properties of the powder and coating are characterized via X-ray diffraction（XRD）, scanning electron microscope（SEM） and energy dispersive spectroscopy（EDS）. Oxidation resistance at 1500 ℃ in static air and ablation resistance under oxygen-propane torch flame at 1600℃, 1700℃, 1800℃ of ZrB₂-SiC coating are tested, Several conclusions are summarized:（1）ZrB₂-SiC composite powders prepared by spray drying possess the character of uniform composition and good flow properties, the particle size D50 is about 40μm, which is suitable for atmospheric plasma spraying.（2）With the spray drying ZrB₂-SiC composite powders as raw material, the ZrB₂-SiC composite coatings are prepared on C/C substrate by atmospheric plasma spraying, the analysis of the coating shows that the structure of ZrB₂-SiC coating is dense, Si in the powder is uniformly distributed throughout the coating, the bond strength between coating and substrate reaches up to 5.72 Mpa.（3）After oxidation at 1500 ℃ for 2h, 3h, 4h, the weight of ZrB₂-SiC coated C/C composites increases with 3.39%, 2.95% and 4.25%, respectively. The ZrB₂-SiC coating effectively improved the oxidation resistance of C/C composites.（4）After ablation at 1600℃, 1700℃ and 1800℃ for 300 s, the weight of ZrB₂-SiC coated C/C specimen increases with 0.63%, 0.76% and 0.71%, respectively. while after ablation for 600 s, the mass ablative rate of the coated specimen is 9.42×10-5 g/s, 2.04×10-4 g/s and 1.04× 10-3 g/s, respectively. The ZrB₂-SiC composite coatings can effectively enhance the ablation resistance of C/C composites.