Research On Structures And Properties Of C/C-SiC Composites Prepared By LSI Process

C/C-SiC composite is a kind of high-temperature structural material and functionmaterial and has been widely researched and applied in many fields. It has thecharacteristics of low density, good oxidation resistance and corrosion resistance andexcellent friction and wear properties. However, the high production cost greatlylimits its applications in the areas of friction. In order to expand its application fields,this paper adopts the LSI method to prepare C/C-SiC composite. This method hasadvantage of short preparation time and low producing cost. The Si-C reactionprocess is analyzed, and the influences of different C/C preform densities andstructures on the mechanical properties and friction and wear properties of C/C-SiCcomposite are also studied. The friction and wear mechanisms are briefly studied aswell. The conclusions are shown as below:(1) C/C-SiC composites with different C/C preform densities and structures areprepared by LSI method in this stduy. The preparation time is short and productioncost is low.(2)The residual Si ineluctably exists in C/C-SiC composite prepared by LSImethod, and distributes in SiC. There are two distribution states of SiC, onedistributes around the matrix C continuously, homogenously and with a net-likestructure, the other distributes in Si in the form of particulate. The SiC easily cracksdue to mismatch of the expansion coefficient between SiC and C. The cracks providechannels for liquid Si and C to further reaction. The interface of pyrolytic carbon andresin carbon is physical bond, and bond strength is weak. The interface of pyrolyticcarbon and SiC is chemical bond, and bond strength is high.(3)The mechanical properties of C/C-SiC composites prepared with the performdensity of1.45g/cm3,1.55g/cm3and1.65g/cm3increase after LSI. The compressionstrength increases more significantly with the increasing rate at approximately50%.As preform density increases, the mechanical properties improve accordingly. But theflexural and shear strength of C/C-SiC composites are lower than that of the high-density C/C composites. The compression strength in X,Y orientation ofC/C-SiC composites is high than that of high-density C/C composite. In Z orientation,the compression strength of C/C-SiC composites with the preform density of1.45g/cm3,1.55g/cm3are lower than that of high-density C/C composite, while whenthe preform density is1.65g/cm3, the compression strength is higher than that ofhigh-density C/C composite. The orientation of compression fractures of differentC/C-SiC composites are diagonal in XY orientation, while it is consistent with theload direction in Z orientation.(4)The mechanical properties of C/C-SiC composites prepared with weftlessneedled felt are better than PANOF needled whole felt when preform density is1.45g/cm3. The fracture behavior of C/C-SiC composite prepared with PANOFneedled whole felt is brittle. While the fractures of C/C-SiC that prepared withweftless needled felt show pseudoplastic characteristics, and are step-like in XYorientation.(5) When the preform density is above1.40g/cm3, the friction coefficient ofC/C-SiC composites increases at first and then decreases with increasing of preformdensity. The wear loss shows the same trend. The friction and wear properties ofC/C-SiC composite with the preform density of1.45g/cm3is optimal. The frictioncoefficient is0.462, the linear wear loss is0.600μm/time, the mass wear loss is0.197g/time.(6)Compared with C/C-SiC composite prepared with weftless needled felt, theC/C-SiC composite prepared with PANOF needled whole felt with the preformdensity at1.45g/cm3has the approximate friction coefficient, lower wear rate,shorter brake time, higher moment stability coefficient,(7)When the preform is weftless needled felt and the density at1.45g/cm3, thefriction coefficient is smaller, the wear volume is lower, the braking time is shorterwith the increasing of the friction pressure and rotate speed.