Study On Preparation Process And Properties Of Carbon Fiber Reinforced SiC Composites

Silicon carbide ceramics have the excellent properties,such as high strength and modulus,excellent abrasive resistance in mechanical properties,low thermal expansion coefficient,high thermal conductivity and good temperature resistance in thermodynamics.In the meantime,silicon carbide ceramics have great application potential in precision bearing parts,wear resistant seals,machined abrasives,gas rotors,compressed cylinders,and so on,which due to its excellent oxidation resistance,good corrosion resistance and chemical stability.Besides that,with the vigorous development of the aerospace industry,silicon carbide is considered to be a novel material with great potential for manufacturing mirrors,which attribute to its high specific stiffness,low thermal deformation coefficient,radiation resistance,good thermal stability and excellent seismic performance etc.However,the Si C mirrors,made by conventional methods,have a series of shortcomings,such as low accuracy and lightweight extent,low fracture toughness and high stress level,and so on.Therefore,it still needs further research for the preparation of silicon carbide composites,in order to obtain higher precision mirrors.For the preparation of raw slurry,thermosetting phenolic resin were used as binder because of the highest carbon content in the three most commonly used resins;To solve the problem that the resin has high viscosity,and it is not easy to mix with other raw material,ethylene glycol is used as diluent.It can be dissolved with the resin,and dilute the phenolic resin,and be the main solvent for the slurry;Benzene sulfonyl chloride,a kind of acid curing agent,is used as resin curing agent,which can make phenol formaldehyde resin cured quickly at lower temperature;Si C powder,with the size of 1200 mesh and 240 mesh,were used as the main solid in the slurry.Polyethylene glycol as dispersant was selected to deal with the problem that the silicon carbide is easy to be reunion;In addition,the nano-carbon black is added to the slurry at the later stage to increase the carbon content of the slurry.Ball-milling process is used to make the components of slurry mixed homogeneously,and the optimum content of each components is determined by the viscosity of slurry,the volume variation after curing,green density and the morphology of carbonization.The research results show that the optimum content of dispersant is 15wt% in the solid phase,and the best content of curing agent is 6wt% of the resin,and the optimum solid content is 60wt%,and the optimum ratio of the two different size of Si C particles in solid phase is 1:1,and the best content of carbon-black accounts for 10wt% of the Si C content when the slurry is mixed with the fiber,and the optimum ratio of the resin and ethylene glycol at 1:10.In order to improve the toughness of ceramics,reinforcement is introduced into Si C ceramics.In this paper,the carbon fiber plain cloth is used as the reinforcement of Si C ceramics.And in order to prevent being damaged during the sintering,the coating was prepared above the carbon fiber,this paper select high temperature zirconia as coating material.And the study results show that the best carbon fiber coating is 4 layers of Y-Zr O2.The Si C ceramic matrix composites were prepared by laying the slurry and carbon fiber layer by layer,curing,carbonizing and reaction sintering.By testing the physical and mechanical properties of Si C ceramics,it was found that the volume density and flexural strength of Si C ceramics decreased and the fracture toughness increased for the introducing of carbon fiber and carbon fiber treated by coating.This paper studied the effect of Si C/C ratio on the properties of Si C ceramics,because of the low flexural strength of the composites.Research results show that the performance of Si C ceramics obtained by reaction sintering is much better when the ratio of Si C to C is 8:3.And the density is 3.066g/cm3,the relative density is 95.8%,the residual silicon is 8.59%,the bending strength is 485.08±53MPa,the fracture toughness is 4.806±0.175 MPa.m1/2,and the hardness is 14.77±0.93 GPa.Compared with Si C ceramics produced by enterprises,the Si C,prepared in this study,has improved mechanical properties of bending strength and fracture toughness in two ways.