| The development of aviation technology puts forward higher requirements for the aircraft braking system. C/C composites exhibit attractive properties such as high strength-to-weight ratio, excellent mechanical properties at elevated temperatures, good friction and wear properties. Due to these characteristics, C/C composites have become ideal material for aircraft brake disk, and been widely used in civil and military aircraft brake device. However, C/C brake material are easy to be oxidized in high temperature oxygen atmosphere, which cause the mechanical properties and friction performance degradation. Therefore, applying oxidation resistance coating on the brake disks is vital to ensure the safety and reliability of braking process. In recent years, the development of heavy fighter makes the temperature of thermal storage up to 900°C in braking process, borate or phosphate coatings are faced with the challenge of weak oxidation resistance. Therefore, it is needed to develop an oxidation resistance coating which can meet the protection requirements, and suitable for industrial production with low cost.In this paper, borosilicate glass was used as the coating material by investigating the oxidation resistance of glass coating. The wettability of glass and C/C brake materials was improved by amorphous SiCN ceramic. What is more, B4 C and Al2O3 ceramic powders were doped to enhance the oxidation resistance of coating. The conclusions were as follows.1. Oxidation resistance properties of borosilicate or phosphate were studied.（1） Borosilicate glass possessed poor wettability to carbon, the coating formed on the surface of C/C was non-dense.（2） Phosphate has good wettability on carbon, the weight loss of coated sample was 22.58% after oxidation at 800°C for 10 h. The reduction of oxidation resistance was caused by the volatilization of phosphate at high temperature.（3） The weight loss of borosilicate/phosphate coated samples was 10.72% after oxidation at 800°C for 10 h.2. A new method is proposed for improving the wettability of glass and C/C brake material by applying ceramic derived from polymer. The structure of SiCN/glass multilayer coating was designed and the as-prepared coating was dense.（1） The structure of SiCN transition layer pyrolysed by polysilazane was complete.（2） The glass coating formed on the surface of modified C/C exhibited dense structure and good adhension with the substrate, and thickness was about 30 μm.（3） The weight loss of SiCN/glass coated sample after oxidation at 800°C for 10 h was 5.66%. The oxidation process was controlled by the diffusion rate of oxygen in the defect of the coating.3. Oxidation resistance properties of SiCN/glass coating modified by B4 C and Al2O3 ceramic powder were studied.（1） After oxidation at 800°C for 10 h, the weight loss of coated sample modified by B4 C was 2.48%. The self-sealing ability of the coating was improved by B4 C.（2） After oxidation at 800°C for 10 h, the weight loss of coated sample modified by B4 C and Al2O3 was 0.51%. The volatilization of B2O3 was inhibited by Al2O3.（3） After oxidation at 700°C or 900°C for 10 h, the weight loss of coated sample modified by B4 C and Al2O3 were respectively 0.12% and 0.29%, which indicated that the oxidation resistance of the coating at low and medium temperatures was excellent.4. Oxidation resistance properties of SiCN/glass-B4C-Al2O3 coating under fresh water and sea water condition were studied.（1） The weight loss of coated sample was 1.20% after oxidation at 900°C for 10 h under fresh water condition. The volatilization of B2O3 was promoted by water and lead to the coating damaged.（2） The weight loss of coated sample was 3.02% after oxidation at 900°C for 10 h under sea water condition. Alkali metal ions catalyze the oxidation of C/C material and increase the oxidation rate of substrate.5. Thermal shock resistance property of SiCN/glass-B4C-Al2O3 coating was studied. The weight loss of coated sample was 0.23% by thermal shock test in air between room temperature and 900°C. The coating was compact without obvious large cracks or spalling after test, which indicates the coating has good thermal shock resistance. |
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