Investigation On Fabrication And Performance Of C/C-SiC Composites For Tank Clutch

C/C-SiC composites are used as the dry friction materials for its excellent properties such as low density, high thermal shock resistance, well anti-oxidation and friction properties. Based on the background of the wet friction material of tank clutch, the fabrications and friction properties of the C/C-SiC composites were studied. Furthermore, the friction and wear properties for C/C-SiC composites and powder metallurgy friction material as tank clutch were compared and investigated.A novel method to fabricate the C/C-SiC composites was proposed, via using the 3D needle-carbon fiber felts as preform and well dispersing fine silicon particles by ultrasonic vibration. This route overcomes the shortcoming of current fabrication techniques, and is efficient way to prepare the C/C-SiC composites with excellent performance and low cost. With the density of the preform increasing, the dimension and the content of impregnated silicon powder decreased. In addition, the silicon powders were distributed uniformly in the preform of needle-punching carbon felt by ultrasonic vabration.C/C-SiC composites with needle-punching carbon felt as perform were fabricated by impregnating silicon through ultrasonic vibration, chemical vapor deposition (CVD), siliconizing and liquid pitch impregnation- carbonation technique. The effect of different SiC contents on mechanical properties and wet friction and wear properties of C/C-SiC composites were investigated.C/C-SiC composite used as the wet friction environment was proposed. The results of wet friction tests of the C/C-SiC composites with different densities perform and 65Mn wet friction pairs show that these materials have the dynamic friction coefficient between 0.09 and 0.13, and up to 85% friction coefficient stability, which is obviously better than the ones of service wet friction materials (friction coefficient: 0.06-0.09, stability: less than 80%). The friction energy of the C/C-SiC composite is 2.28 and 1.90 times of ones of service clutch materials, respectively; the energy load is 48 times of standard energy. These materials have high energy load, high dynamic friction coefficient, stable friction coefficient and low abrasion, which indicate that the C/C-SiC composite is an excellent wet friction material. These composites broaden the application field of C/C-SiC composites, and are applied to large-scale production.According to the microstructure of the C/C-SiC composites' surface, the friction surface was completely covered with nanometer oil film, and the structure model of surface appearing "brush shape" was founded. The brake process of C/C-SiC composites follows the friction course of fluid lubrication-boundary lubrication-mixed lubrication-thin film lubrication.The three-point bending strengths, inter-laminar shear strengths and compressive strength of the C/C-SiC composites were tested and analyzed. The results show that with the densities of perform increasing the SiC content decreases from 27wt% to 14wt%, the bending strength from 41.4MPa to 432MPa and the compressive strength from 103.5MPa to 142.MPa. The inter-laminar shear strength of materials is 6.5-9.5MPa. With the increase of carbon felt densities, the rupture of the material changes from brittle rupture to "pseudo-plastic" rupture.The wet friction and wear performances of C/C-SiC composites under the simulating condition with different initial velocity, brake specific pressure and absorbing energy were tested. The results indicates that C/C-SiC composites possess excellent wet friction and wear properties, and its high and stable friction coefficient can be kept at different braking velocity and braking pressure. After 300 times friction test, the wear rate is zero.The copper-based powder metallurgy friction material as tank clutch as well as the wet friction properties was fabricated. The results show that it's effective to improve the surface wet ability between the material and lubricating oil, and enhance the adhesive ability of the material surface by adding spherical graphite and short chopped carbon fiber. The friction coefficient of this material is 0.08-0.11, and its friction energy is 1.86 times and 1.55 times of service clutch materials. Its energy load is 6.7 times of standard request.The constant-velocity friction test between C/C-SiC composites and 30CrSiMoVA steel was conducted. The dry brake performances of two friction pairs of C/C-SiC composites, the friction pairs between C/C-SiC composites with C/C composites, 30CrSiMoVA steel and Fe-based powder metallurgy material were studied, respectively.A 3D cycle-symmetric finite element model was set up by ANSYS software, and the wet brake process of C/C-SiC composites was simulated. Finally, the temperature and the thermal stress changes of different positions with different time were described.