Microstructure And Tribological Behavior Of C/C-SiC Braking Composites Fabricated By Chemical Vapor Infiltration Process

C/C-SiC friction composites have been intentioned widely due to some excellent performance, such as low density(≤2.40g·cm-3), high strength, high friction coefficient and stability coefficient, good wear resistance, high adaptable and long life。Based on the background of the C/C-SiC braking composites for the high-speed and high-energy braking system, Chemical Vapor infiltration process (CVI) has been used to fabricate C/C-SiC composites in present research. Then, properties of CVI-C/C-SiC composites have been investigated through microstructure, thermal conduction properties and mechanism, mechanical properties and failure mechanism, oxidation behavior and mechanism, and tribological behavior. Furthermore, the results have been compared with RMI-C/C-SiC composites which have been widely used in engine application. Main research contents and results as follows:(1)2.5D pinthed carbon felts were taken as perform. In matrix, SiC was mainly found around the region of less density of carbon fibers with the cauliflower surface, which fromed during the CVI process. Mechanism of formation of SiC during CVI process was studied systematically, and main interface structure in C/C-SiC composites has been represented.(2) The influence of fabrication process on morphology and capability of SiC layer in C/C-SiC composites have been studied. SiC layer in CVI-C/C-SiC composites was more continuous and compactable than that in RMI-C/C-SiC composites. (3) The influence of fabrication method and composition on thermal conduction has been researched.(4)The mechanical properties of C/C-SiC composites and effections have been studied. C/C-SiC composites fabricated by CVI process exhibited excellent toughness, and main toughening mechanism is deflection of crack, bridging of fibers, furcation of crack, fiber pull-out and interfacial debonding.(5) The influence of time, temperature and composition on oxidation properties of C/C-SiC composites has been studied. And, the oxidation process and oxidation mechanism has been revealed.(6)The influence of composition, microstructure, and braking condition on frictional properties of CVI-C/C-SiC friction composites has been studied by the MM-1000. Under low-energy and self-ring condition, friction coefficient of CVI-C/C-SiC friction composites was about0.16～0.239. Under high-energy and self-ring condition, friction coefficient was about0.21～0.31. And, friction coefficient was about0.245～0.29under steel-ring condition. However, friction coefficient of RMI-C/C-SiC under that three condition were0.30,0.336and0.34, respectively, which were higher than that of CVI-C/C-SiC friction composites.(7) The wear mechanism of CVI-C/C-SiC composites under different braking conditions has been studied. Grain wear was main wear form under the low-energy and self-ring condition. Oxidation wear and grain wear were main wear form under the high-energy and self-ring condition. Furthermore, grain wear and adherent wear were main wear form under the steel-ring condition.(8) Under low-energy and self-ring condition, there was an obviously influence of superficial hardness on mechanism of wear during braking process. When superficial hardness was higher than98.2RHA,"Ploughing efficient" was changed to "Grinding efficient"."Grinding efficient" will leave a great amount of tinny scripts on friction surface, which resulting in the decrease of superficial roughness.Through this research, Study and understanding of tribological properties for C/C-SiC frictional composites has been enriched and improved, and it is valuable to expand the application fields of C/C-SiC friction composites.