Preparation And Properties Of Chopped Carbon Fiber Reinforced C_f/SiC Composites

Carbon fiber reinforced silicon carbide matrix composites?C_f/SiC composites?have lots of advantages,including high temperature resistance,corrosion resistance,high specific stiffness,high thermal conductivity,low density and so on.What's more the unique energy dissipation mechanisms,such as crack deflection,fiber extraction,and fiber debonding,lead to the non-catastrophic failure like metals and greatly improve its reliability in engineering applications.Therefore,the C_f/SiC composites are widely used for high-temperature structural materials in aerospace,military,energy and other fields.However,the C_f/SiC composites fabricated from continuous carbon fiber show greatly different physical and mechanical properties in different directions,limiting the application as precise elements.Therefore,it is significant to investigate the fabrication of the isotropic C_f/SiC composites.In this work,short cut carbon fiber was used as the reinforced phase to fabricate highly dense and isotropic C_f/SiC composite by slip casting and reaction sintering.Influences on the microstructure and performances of C_f/SiC composites are investigated,including volume content of carbon fiber,particle size,grain composition,dispersant content,binder content,mixing time and feeding mode.Viscosity of slurry would exert great influences on the discharge of gas and filling in the process of slip casting,and then the structure of green body as well as the reactive melt infiltration.It is concluded from the results that low-porosity green body is realized without agglomeration when 0.1 wt.%TMAH is added into the slurry.In addition,4 wt.%PVP added into the slurry leads to green body with high apparent porosity?45.98±0.37%?,which helps to the reaction sintering.The viscosity decreases with the time and no apparent effect of feeding mode is observed on the slurry and green body.Higher content of binder PVP contributes to higher viscosity.More space resistance resulting from higher carbon fiber content tend to cause the inhomogeneous dispersion.What's more,bulk density of green body decreases with the higher carbon fiber content due to its low density.The investigation on the effect of SiC particle shows that larger particle lead to low porosity of green body and the grain composition of 50 and 5?m SiC realizes the lowest porosity?41.88±0.78%?.Highly dense and well-performed C_f/SiC composites are fabricated by reaction sintering.The results demonstrate that C_f/SiC composite with 35 vol.%carbon fiber exhibits the maximal flexural strength?412±47 MPa?.However,excessive carbon fiber would result in more defects and weaken the performance of composites.It is noticed that smaller SiC particles help to reduce the content and size of residual Si with high brittleness,which greatly enhances the composites.The composites with grain composition of 50 and 5?m SiC shows the highest flexural strength?357±41MPa?.The composites with PVP as binder show high density and low porosity.4 vol.%PVP leads to the best mechanical properties?flexural strength 432±39 MPa?for the formation of fiber-shaped?-SiC.Pyrolytic carbon from resin in the process of impregnation and pyrolysis protects the carbon fiber from damage in reaction sintering.The densification and mechanical properties are improved with the increasing of resin content.However,excessively high concentration of resin causes very low porosity of green body,which hinders the infiltration of melting Si and densification of C_f/SiC composites.