Study On Preparation And Mechanical Properties Of C/C Composites Reinforced By Multicomponent Carbon Nanomaterials

Carbon/carbon(C/C)composites are composed of carbon fiber and carbon matrix,which have low density,high specific strength and excellent high temperature performance.So,it is widely used in the aerospace field.In the past,the rapid development of the aerospace field has put more and more stringent requirement on the structure and performance of C/C composites.The carbon matrix of C/C composites has low strength and high brittleness,and there are a large number of unreinforced carbon matrix between layers,layers,and between bundles.In the process of processing,the fibers become shorter and the reinforcement effect is greatly weakened,resulting in low-stress failure of the composites.In response to this problem,this article uses the injection method and the catalytic chemical vapor deposition(CCVD)method to introduce carbon nanotubes(CNT)and reduced graphene oxide(rGO)into the carbon fiber preform to construct a multi-element,multi-scale hybrid CNT-rGO-carbon fiber preform.Then,the CVI method is used to prepare high-performance C/C composites reinforced by carbon nanomaterials.On this basis,the influence of CNT and rGO on the deposition rate,microscopic morphology and structure of Py C was studied;the toughening mechanism of CNT and rGO on C/C composites and the influence on mechanical properties were discussed.The main contents and conclusions are as follows:(1)Research on the process of rGO modified carbon fiber preform and the process of preparing CNT by CCVD.By adjusting the concentration of GO dispersion and the number of cyclic injections,the content control of rGO in the carbon fiber preform was achieved.By optimizing the process parameters,the growth of CNTs on the surface of carbon fibers was realized.Studies have shown that under this process condition,CNTs grow with a"top growth"mechanism.Under the process conditions of a catalyst precursor concentration of 2 wt.%,a CH₄ gas flow rate of 300 m L/min,a growth temperature of 1050°C,and a growth time of 2h,the CNT content in the carbon fiber preform is 7.75 wt.%,and the CNT distribution on the carbon fiber surface is uniform,The length is more than 10?m and the diameter is about 200 nm.Finally,rGO and CNT were successively introduced into the carbon fiber preform to prepare the CNT-rGO-carbon fiber preform.(2)The influence of CNT and rGO on the deposition rate and structure of the substrate Py C.XRD,SEM,PLM and Raman spectroscopy were used to characterize the microscopic morphology and structure of the composites,and the effects of rGO and CNT on the deposition rate,microscopic morphology and texture of Py C were analyzed.Research shows,rGO and CNT can accelerate the early deposition rate of Py C and reduce the texture of Py C.Add CNT will have a"fine grain"effect,while around the CNT Py C deposition,"CNT/Py C core-shell structure."(3)The toughening mechanism of CNT and rGO on C/C composites and their influence on mechanical properties.Through the mechanical performance test of the composite material and the analysis of the cross-sectional microstructure,the toughening mechanism of carbon nanomaterials in C/C composites is proposed.Studies have shown that after the introduction of rGO,a layer of low-texture Py C will be formed on the surface of the carbon fiber,reducing the ring-shaped cracks at the interface between the carbon fiber and the Py C matrix.After the introduction of CNT,CNT promotes the nucleation of Py C,refines the Py C grains,toughens Py C,forms a CNT/Py C core-shell structure,reduces ring-shaped cracks in the matrix,and improves mechanical properties.The flexural properties,compression properties,fracture toughness and microhardness of composite materials were tested.The results show that compared with C/C composites,the three-point bending strength,out-of-plane compressive strength,in-plane compressive strength and fracture toughness of CNT-rGO-C/C composites are increased by 29.7%,37.8%,28.4%,and 24.6%,respectively.The hardness of zone 1,zone 2 and zone 3 increased by 44.7%,19.9%,4.5%respectively.