Research Of In-situ Grown ZrC_NWS/NTSModified Carbon/Carbon Composites

The C/C composite material have a series of excellent properties,including low density,high specific strengths and modulus,low coefficient of thermal expansion,good friction and wear,high thermal conductivity,which can be widely used as thermal structural materials in high technology fields such as aerospace.However,the high brittleness of C/C composites and low strength of pyrolytic carbon decrease the mechanical properties of C/C composites,which severely limits its application in sharp sharp edges,thin-walled edges and complex components.In-situ growth of ZrC nanowires and nanotubes(ZrC_NWS/NTS)on the surface of carbon fiber preforms is an effective solution.ZrC nanowires or nanotubes can significantly improve the fracture toughness of C/C composites,narrow the crack size and weaken the crack tip stress through the mechanism of crack deflection and interface area increase.At the same time,the nanomaterials with dense covalent bonds can produce effective stress transfer in carbon matrix,release stress concentration and improve the overall strength of C/C composites.The main conclusions are as follows:In situ growth of ZrC_NWSWS on the surface of carbon cloth was carried out by in-situ pyrolysis of nickel nitrate hexahydrate.The effects of heat treatment temperature and catalyst loading on the microstructure and distribution of ZrC_NWSWS were investigated.In situ growth of ZrC_NTSTS on the surface of carbon cloth was carried out by evaporation and electrophoresis using carbon nanotubes as template.The effects of heat treatment temperature and carbon nanotubes content on the preparation of ZrC_NTSTS were investigated.The results of the study show that:with the higher the heat treatment temperature is,the more ZrC_NWSWS are,and their homogeneity and crystallinity are better.With the increase of catalyst loading,the growth trend of ZrC_NWSWS increased first and then decreased,and the catalyst was higher than the critical value,and the length and diameter of nanowires were smaller.The predominant growth direction of the ZrC_NWSWS prepared by the precursor pyrolysis method is the[111]orientation,and the growth mode of the nanowire is a solid-liquid-solid?SLS?growth mechanism.The ZrC_NTSTS prepared by a combination of thermal evaporation and electrophoresis has a homogeneous diameter and good crystallinity,and the growth mechanism begins at the surface defects of the nanotubes with an axial growth direction of[111]and a radial growth direction of[200].ZrC nanowire modified carbon cloth preform was densified by isothermal chemical vapor infiltration process,and the effects of different loading amount of catalyst and different ZrC_NTSTS content on texture and densification rate of pyrolytic carbon matrix were studied.The results of the study show that:With the introduction of ZrC_NWS/NTSWS/NTS into C/C composites,the deposition rate can be increased obviously at the early stage of densification.However,With the increase of ZrC_NWS/NTSWS/NTS content,the interface between the reinforcements and the matrix increases,and the apparent density of C/C composites decreases due to the increase of pores in matrix.The matrix carbon grains at the interface of the fiber and matrix are refined,and the optical activity is low texture and isotropic pyrolytic carbon,but far away from the interface is high-textured pyrolytic carbon.With the increase of the content of ZrC_NWS/NTS,the crack length and pore diameter were decreased,and the degree of crystallization perpendicular to?002?crystal plane was increased,while the order of pyrolytic carbon was decreased slightly.The mechanical properties of C/C composites with different catalyst loading and different ZrC_NTSTS contents were studied,and the influence mechanism of ZrC_NWS/NTSWS/NTS on the mechanical properties of C/C composites was analyzed.The results show that:With the introduction of ZrC_NWS/NTSWS/NTS composites,the strong interfacial bonding between the matrix and the fibers in the C/C composites was weakened,and the flexural strength was significantly increased and the fracture toughness was significantly enhanced.With the introduction of ZrC_NWS/NTS,the compressive strength of C/C composites also increases due to the reduction of the number of annular cracks between the fiber and the matrix.The thermophysical properties of C/C composites with different catalyst loading and different ZrC_NTSTS contents were studied,and the influence mechanism of ZrC_NWS/NTSWS/NTS on the thermophysical properties of C/C composites was analyzed.The results are as follows:After introducing ZrC_NWS/NTSWS/NTS into C/C composites,the thermal conductivity of C/C composites is improved due to the high intrinsic thermal conductivity of ZrC and the decrease of internal defects of composites.The introduction of ZrC_NWS/NTSWS/NTS can significantly improve the thermal expansion coefficient of C/C composites,which is related to the large intrinsic thermal expansion of ZrC,and with the increasing of ZrC_NWS/NTSWS/NTS content,the coefficient of thermal expansion increased significantly.When the temperature is lower than 1500°C,the change of thermal expansion coefficient of C/C composite is stable due to its high melting point,high binding energy and small atomic amplitude.