Construction And Properties Of Antioxidant C/C-ZrC-SiC Composites Based On Sugar-carbon Conversion

C/C composites have been widely used in rocket engine nozzles and missile nose cones for their light weight,high specific strength,high specific modulus,high thermal conductivity,low thermal expansion coefficient and wear resistance.However,the C/C composites begin to oxidize in the oxidizing atmosphere above 450?,which destroys the structural integrity and limits their development and application in space technology.In order to improve the mechanical properties and high temperature oxidation resistance of C/C composites,a low density C/C composite was prepared by sol-gel method.Compared with the traditional asphalt carbon and resin carbon,the low molecular weight ZrC composites were prepared by sol-gel method.In this paper,the ZrC powder was synthesized by sol-gel method,and then made by the precursor infiltration pryrolysis?PIP?.The C/C-ZrC-SiC composites were obtained by matrix modification,and the related properties were evaluated.C/C composites with different densities were obtained by sol-gel method.The influence of process parameters on the material was studied.The technological parameters during the preparation process were optimized,the relationship between material density and mechanical properties was explored,and the fracture mechanism of C/C composites was analyzed.With the increase of the density of C/C composites,the mechanical properties of C/C composites show an increasing trend.Due to the difference of bundle content in different directions of carbon fiber preforms,the bending performance in z direction is higher and the compressive strength is lower than that in x/y direction.ZrC powder was designed and synthesized.The effects of C/Zr molar ratio,carbothermal reduction temperature and holding time on the synthesis of pure ZrC powders were studied.The results show that the lower the C content,the lower the reaction activity and the higher the reaction temperature,but the higher the C/Zr molar ratio,the longer the time of carbohydrate-carbon conversion.When the C/Zr molar ratio is 5:1,the ZrC of pure phase is most easily obtained.The temperature required for carbothermal reduction can be reduced from 1600?to 1500?by increasing the temperature of 1200?for 2 h in the carbothermal reduction process.C/C-ZrC composites were prepared by precursor impregnation and pyrolysis.The effects of ZrC content on the mechanical properties of C/C composites were investigated.The mechanical properties of C/C-ZrC composites were significantly improved compared with those before.Among them,the flexural strength in the x/y direction increased from 79.01MPa to 154.79MPa,the compressive strength in the z direction increased from 92.18MPa to 158.31MPa,the compressive strength in the x/y direction increased from 53.42MPa to 147.13MPa,and the compressive strength in the z direction increased from 28.92MPa to 106.09MPa.The mechanical properties of C/C-ZrC composites increase with the increase of impregnation times of ZrC precursors.Subsequently,polycarbosilane?PCS?was used as precursor to further improve the density of C/C-ZrC composites by PIP method,and C/C-ZrC-SiC antioxidant composites were constructed.The effects of SiC addition on the micro-morphology and mechanical properties of the composites were studied.The mechanical properties of the composites can be further improved by adding SiC.The flexural strength in the x/y direction increases to 176.81MPa and 184.39MPa in the z direction.The compressive strength increases in x/y direction to 197.40MPa and z direction to144.53 MPa.In addition,the strength difference of the two composites before and after the introduction of SiC is similar,and the increase range is lower than that of ZrC.Static oxidation tests were carried out on C/C-ZrC-SiC composites to explore the macro-morphology,micro-morphology,weight loss and phase change of the composites under different oxidation temperature and time.The experimental results show that the longer the oxidation time is,the higher the oxidation temperature is,the more SiC content is,and the oxide film formed by the reaction.The thicker the composites,the better the oxidation resistance.When the oxidation time is more than 15 minutes,SiC is completely converted to SiO₂.The materials with more ZrC content show better oxidation resistance.