The Fabrication And Mechanical Properties Of C_f/SiC(O) Cornposites Via Precursor Infiltration And Pyrolysis Process

Carbon fiber reinforced silicon carbide(Cf/SiC)ceramic matrix composites possess high strength,low density,and excellent heat resistance,which present a great potential in the aerospace area.However,the complicated preparation of Cf/SiC,limits its wide application largely.To overcome this problem,the precursor infiltration and pyrolysis process(PIP)is adopted to manufacture the Cf/SiC,and become a current research hotspot gradually,which is due to the lower sintering temperature,much simple process and the avaliblity for complex components.In this paper,Cr/SiC composites were prepared by PIP method with olysilyacelene(PSA)as SiC precursor.The effects of the first-cycle pressure curing process on the mechanical properties and microstructure of the composites were mainly studied.Then the pyrolytic carbon layer was also used to improve the interface structure.Firstly,the chain structure,crosslinking mechanism and pyrolysis behavior of PSA precursors were in this paper analyzed.The test result demonstrated that the PSA chain structure linked with-CH3SiH-and alkynyl bond alternately,and its ceramic yield at 1000?was 81%.The group changes of PSA during its conversion into ceramics were investigated.At 200?,PSA crosslinked via hydrosilylation reaction,which the Si-H bond and alkynyl group disappear to generate a three-dimensional network.At 1000?,the Si-CH3 bond disappears,PSA transformed to amorphous SiC completely.At 1200?,amorphous SiC turn from amorphous state to 3C-SiC.Secondly,the Cf/SiC composite was prepared and pressure-cured in the first cycle during the PIP process.It was found that the best heat preservation time before the first cycle was 15 minutes,the pressure was 1 MPa,and the pyrolysis heating rate was 5?/min.Cf/SiC composites prepared in 9 PIP cycles with process parameters above have the best mechanical properties,with a flexural strength of 111 MPa and a density of 1.67 g/cm3.When the holding time before pressing is too long,the density of the prepared Cf/SiC composite decreases,and a large number of closed pores appear inside the material;and the excessive pressing pressure will also cause damage to the internal matrix and carbon fiber,resulting in a decrease in material properties;If the pyrolysis heating rate is too fast,the bonding strength between the fiber and the matrix is too large,which reduces the ability of the fiber to pull out.In order to reduce the interface bonding strength between the fiber and the matrix,phenolic resin was used as carbon source to form the carbon interface between carbon fiber and matrix.The preparation of carbon interface was performed by PIP process.When the PIP cycle was 3 times,the prepared carbon interface was the best,which can fully cover the carbon fiber without causing excessive adhesion among the fibers.Within this carbon interface treated preform,Cf/SiC composite material was prepared after 9 PIP cycles which had a flexural strength of 164 MPa and a density of 1.56 g/cm3.The mechanical properties were significantly improved with the pyrolysis carbon interface layer.