Rmi Prepared By The C / C-sic Composites And Their Performance

Braking materials is the critical part for the movement of train, especially high-speed train. The C/C-SiC composites have low density, high anti-thermal shocking, excellent oxidation resistance and good friction properties. The composites manufactured by reactive melt infiltration (RMI) have such many advantages as shorter manufacturing time and lower cost.In order to obtain the C/C-SiC composites as braking materials for high-speed train, the C/C-SiC composites were manufactured by RMI with needle felt as preform in this paper. By means of scanning electron microscopy (SEM), optical microscopy (OM), X-ray (XRD) and Raman, the effects of various carbon matrixes, temperature of melt silicon and high temperature treatment on the behaviors of melt silicon infiltration into the porous C/C composites and mechanical properties and the effects of different carbon coatings on the mechanical properties of composites were investigated. The dependences of the friction and wear properties on various carbon matrixes, the composites, environments (including humidity and temperature), and braking energy were also discussed. The conclusions can be drawn as the following:(1) According to the theoretical calculation, the porous C/C preforms with uniform pores radius from 10 μ m to 1300 μ m are beneficial to infiltration of liquid silicon. The growth of SiC was controlled by the self-diffusion of carbon atoms.(2) The resin-carbon matrixes porous C/C composites with high temperature treatment (HTT) have well-distributed pores, and is most beneficial to liquid silicon infiltration. The open porosity and density of C/C-SiC composites is 1% and 2.25 g· cm^-3 respectively. HTT makes the specific surface area of pores larger, resulting in more contact area with liquid silicon and more SiC.(3) The C/C-SiC composites with pyro-carbon coating have higher flexural strength (161.5MPa) and better "pesudo-plastic" than resin-carbon coatings. Because the pryo-carbon coating can protect the carbon fiber better during the manufacturing process of composites, the bonding strength between resin carbon and carbon fiber is changed by HTT. The strength of composites with HTT decreases little, but the composites show the "pesudo-plastic". On the resin carbon coatings of compositeswith HTT, the porous C/C composite with final HTT has lower strength, compared with carbonized resin carbon coatings. Both show the "pesudo-plastic".(4) The best friction properties of C/C-SiC composites in the test of simulating brake are that the friction coefficient is 0.34 and wear ratio is 0.54 um/time. In water environment, the composites have the stable friction coefficient, and the wear ratio of both composites and steel counterpart decreases. With the increase of brake energy, the friction coefficient of composites decreases slowly, and the wear ratios of composites increase firstly then decrease. In the test of constant speed, with increasing content of silicon carbide, the friction coefficient and wear ratio of C/C-SiC composites increase firstly and then decrease. As the increase of temperature, the friction coefficient of composites decreases slowly, and the wear ratios of composites increase firstly then decrease.