Microstructure And Properties Of Short Fiber Reinforced C/C-SiC Brake Composites

Abstract:Short carbon fiber reinforced C/C-SiC composites were made by WL-LSI process. Combined with similar materials having been used as brake, the composition of the materials, the structure of the fibers, the physical and mechanical properties, the friction and wear properties were studied respectively under the background of brake application. The effect of fiber content, the microstructure and the braking speed were discussed. By comparing the results, the compition, the microstructure and the properties of C/C-SiC composties for brake application were obtained, also differences between the seil-made materials and the foreign materials which has been used on brake systems were found. The essential causes of this differences were further analyzed in order to manufacture new C/C-SiC brake material with more excellent properties. Main research contents and results are as follows.(1) The composition of C/C-SiC composites, the distribution and orientation of carbon fibers, fiber morphology, matrix morphology and fiber/matrix morphology were studied. The results show that:the composition of C/C-SiC composites preparation by WP-LSI process were Carbon, β-SiC, Silicon and similar materials were made of C, β-SiC, α-SiC, Silicon; Short carbon fiber in self-made material are preferred orientation and SiC matrix filling C/C substructure. SiC matrix were formed by three steps.(2) The mechanical properties and failure mechanisms of C/C-SiC composites were analyzed and the effects of carbon fiber content on the mechanical properties of materials were discussed. The results showed that:the mechanical properties of self-made C/C-SiC composites improved, with the increasing of fiber content. When the fiber content is30%, the flexural strength was104.63MPa, the compressive strength of perpendicular and parallel were167.99MPa and90.03MPa respectively; Failure mechanism changed from brittle fracture to pseudoplastic failure.(3) The friction and wear properties of C/C-SiC composites were tested by QDM150machine and discussed the effects of braking speeds and fiber content on the friction and wear properties. The results show that:the coefficient of friction at different speeds maintained at between0.30and0.55and the amount of wear maintained between0.01-0.04cm3/MJ. Braking curves at higher speeds were smoothly, with optimum friction and wear properties. At low friction speed process, due to asperities hire of the sample surface, it was abrasive wear. At high friction velocity, friction film appears and showing abrasive wear and fatigue wear. Fiber content of30%of the C/C-SiC composites at constant speed friction experiments has a better overall friction and wear properties than the materials whicn the fiber content was20%.(4) The friction and wear properties of C/C-SiC composites were tested by MM-1000machine and the effects of braking speed on the friction and wear properties were studed. The results showed that:with the increasing of the braking velocity, the coefficient of friction reduced, maintained at between0.3and0.4and the stability coefficient improved, maintained at between0.65and0.70. The amount of wear of the composite and steel couples increased with the increasing of braking speed and the wear mechanism changed from abrasive wear wear into integrated into abrasive wear, oxidation wear and fatigue wear.(5) By improving the WP-LSI technology, we can Reduce costs preparation of short carbon fiber reinforced C/C-SiC brake materials.