Research On Preparation And Performance Of TiB₂ Reinforced C/C Composite

Materials are important promoters of technological development.Since the"Shenzhou V"manned spacecraft successfully completed its mission,my country's aerospace industry has developed rapidly.New type of extreme environment materials such as high temperature resistance,low density and high strength.Since its inception,carbon/carbon(C/C)composite material has been a special application material in aerospace,electrical and electronic,and high-temperature special fields due to its excellent properties such as low density,high electrical conductivity,high thermal conductivity,and high temperature resistance.Due to the long preparation cycle of C/C composite materials and low raw material utilization rate,the cost of C/C composite materials is high,which restricts its development.In addition,the oxidation performance of C/C composites has always been a fatal defect of C/C composites because they are all composed of carbon.Based on the above two factors,the application of C/C composite material s is restricted.This subject makes an investigation on the low-cost preparation and oxidation resistance of C/C composite materials,and the following results are obtained:Using cheap raw materials such as coal-based mesophase pitch,natural flake graphite,T300 carbon fiber,etc.C/C composite materials with excellent performance were successfully prepared through low-temperature hot pressing and high-temperature pressureless processes.The key to the success of this process lies in the exploration of the coal series mesophase pitch content and low-temperature hot pressing temperature.Therefore,this subject has done two sets of comparative experiments:(1)At the same low-temperature hot pressing temperature(300°C),four different mesophase pitch ratios(40%,50%,60%,67%).(2)With the same mesophase pitch ratio(50%),four different low-temperature hot pressing temperatures(350?,400?,450?,500?).The cracking of coal-based mesophase pitch is analyzed by TGA,the microscopic morphology of C/C composites is analyzed by SEM,and the macroscopic properties of C/C composites are characterized by mechanical properties and density tests.The results show that when the low-temperature hot pressing temperature is 300?and when the volume ratio of coal based mesophase pitch is 50%,the density and mechanical properties of C/C composites are the best,with a density of 1.76g/cm³,a bending strength of 388±16 MPa,and a fracture toughness of6.10±0.83 MPa.m^1/2.Doping TiB₂ in the C/C composite material can effectively inhibit the oxidation of the C/C composite material at low temperatures and improve the oxidation resistance of the C/C composite material.In the traditional CVD/CVI and PIP methods to prepare C/C composite materials,the introduction of ceramic particles is very difficult.The winding method used in this topic can directly introduce ceramic particles into C/C composite materials.X-ray diffraction(XRD)analysis shows that no other impurities are generated when TiB₂ is introduced.Because the particle size of TiB₂ is small and the specific surface area is large,the binding effect of mesophase pitch on the interface is reduced,and its mechanical properties are slightly reduced.The bending strength of C/C-10TiB₂ is 301±12MPa,and the fracture toughness is 5.42±0.87 MPa.m^1/2.The bending strength of C/C-20TiB₂ is 289±16MPa the fracture toughness is 5.11±1.02MPa.m1/2.The weight loss of pure C/C composites reached 54.92%after oxidation at 600°C for 150 minutes,while the weight loss of C/C-10TiB₂ was reduced to 2.6%,and the weight loss of C/C-TiB₂ was only 0.35%.C/C composites and C/C-TiB₂ were successfully prepared through 4steps of pulping,winding,low-temperature hot-pressing densification and high-temperature pressureless carbonization.Compared with the traditional CVD/CVI and PIP,each step of the preparation process has a shorter p eriod,high raw material utilization rate,and one-time impregnation.It is suitable for finished products and lays a solid foundation for subsequent industrialization.Reducing the cost of C/C composite materials from the direction of process simplification is conducive to expanding the application of C/C composite materials and ceramic-based reinforced C/C composite materials.