Preparation And Properties Of C_f/C-SiC-ZrB₂ Composites And Antioxidative Coatings

C_f/C composite materials with light weight,high strength,high modulus,good thermal stability and excellent thermal shock resistance have great potential applications in thermal protection of aircraft nose,nose cones,rocket engine nozzles,throat linings,and combustion chambers.However,the poor oxidation resistance of C_f/C composites severely limits their applications in high temperature oxidizing atmospheres.Aiming at the problem of poor oxidation resistance of C_f/C composites and poor thermal compatibility with anti-oxidation coatings,C_f/C-SiC-ZrB₂ composites were prepared by chemical vapor infiltration?CVI?and precursor infiltration-pyrolysis?PIP?processes to introduce anti-oxidation ZrB₂-SiC ceramics into C_f/C composites.SiC/ZrB₂-SiC/SiC multi-layer anti-oxidation coatings were prepared on the surface of C_f/C-SiC-ZrB₂composites.The mechanical properties,thermophysical properties and anti-ablative oxidation resistance of the materials were investigated.The effects of pretreatment,deposition time and propane content on the properties of C_f/C composites were investigated.Compared with the unpretreated C_f/C composites,the surface of the carbon fiber plate is flat and porous after pretreatment,which is beneficial to the subsequent pyrolytic carbon deposition and PIP process.As the deposition time prolongs,the bulk density of the C_f/C composite increases gradually.At the beginning of the CVI process,as the bulk density of the material increases,the mechanical properties of the C_f/C composite increase gradually.When the bulk density reaches 1.23 g/cm³,the mechanical properties of the material no longer monotonously increase with increasing bulk density.Continued increase in bulk density causes attenuation of mechanical properties.Too high or low propane content is not conducive to the uniform deposition of pyrolytic carbon on the surface of the carbon fiber.When the propane content is 50%,the pyrolytic carbon layer deposited is relatively uniform.C_f/C-SiC gradient composites were obtained by deposited C-SiC gradient substrate on C_f/C composites via chemical vapor deposition,and then deposited SiC matrix with CH₃SiCl₃.The ZrB₂ ultra-high temperature ceramic precursor was synthesized by reacting polyboroxane with organozirconium precursor.C_f/C-SiC-ZrB₂ composites were prepared by infiltrating-pyrolysing of ZrB₂-SiC composite ceramic precursors into C_f/C-SiC composites.The effects of temperatures on viscosity of infiltration liquid,and the pressures and numbers of infiltration on the density of composites were investigated.The optimum infiltration parameters of the ZrB₂-SiC composite ceramic precursor were obtianed.The effects of precursor pyrolysis parameters on the properties of composites were investigated,and the optimal pyrolysis parameters of ZrB₂-SiC composite ceramic precursors were achieved.The composite material has a flexural strength of 315.1 MPa and a fracture toughness of 10.87 MPa·m^1/2 after pyrolysis.To investigate the thermal matching between ultra-high temperature ceramics and C_f/C composites,a ZrB₂-SiC/SiC double-layer coating with MgO addition was first prepared on graphite substrate.MgO promotes densification of the coating and significantly improves the repeatability of ZrB₂-SiC/SiC coatings.The C_f/C composite with ZrB₂-SiC/SiC double-layer coating has good oxidation resistance.The SiC/ZrB₂-SiC/SiC multilayer coating was prepared on the surface of C_f/C-SiC-ZrB₂composite by embedding and brushing process.The mechanical properties at room temperature and high temperature,thermophysical properties,and microstructure of C_f/C-SiC-ZrB₂ composites were characterized.The static oxidation test,plasma ablation and wind tunnel test show that the C_f/C-SiC-ZrB₂ composite and its coating have excellent high temperature resistance,oxidation and ablation resistance.