Study On Preparation And Its Process Of C/C Composites By Electric Heating Method CCD

C/C composites is one of the important materials used in missiles, rockets and aircraft brake pads due to the advantages of high strength, low density, high thermal conductivity, friction performance, and good impact performance.In recent years, C/C composites also gradually expand the amount of usage in the machine wheel guide rail, medical materials, engine blades and piston and other industrial areas.The key of ensuring the excellent performance lies in the preparation process. C/C composites is prepared by the electric heating method CVD (Electrothermal chemical vapor deposition, ECVD) in this experiment, the main purpose is to simplify experimental equipment, shorten the preparation cycle, reduce the cost and has a certain mechanical properties.In this paper, carbon felt as the preform, C2H2 as the carbon source gas, N2 as the dilution gas, The carbon felt is used for direct charging for good conductivity, and the carbon source gas is pyrolyzed by the carbon felt itself. Temperature resistance properties of carbon felt were studied before the experiment, better in the subsequent experiments were carried out to adjust the temperature,and Found that the resistivity of carbon felt decreases with the increasing of temperature.rule of change is ?= ?0(1-4.067 × 10-4t).In this paper, the process conditions of C/C composites prepared by ECVD were studied. The effects of process conditions on the densification of C/C composites were analyzed. Explored the effect of pyrolysis temperature, carbon source concentration on the densification rate of carbon source, found prefabricated body form a certain temperature gradient and sedimentary is divided into dense area, not sedimentary area,porous area three regions. the effect of pyrolysis temperature, carbon source concentration and residence time on composite final density was analyzed, when the C2H2:N2=1:20 received the highest density for 1.55g/cm3, densities of the samples showed a gradient distribution after deposit 30 hours. The carbon yield of the prepared composites was measured, which provides a reference for optimizing the process conditions.Study on the influence of processing conditions of PyC electric heating method on the structure, analyzed the influence of pyrolysis temperature and concentration of carbon source on PyC. Found the specific processing conditions, C/C composites can grow ball, the ball rod, cotton and so on the many kinds of shapes of dot PyC, put forward the rain distribution, branches distribution and tangles distribution and so on Three kinds of nucleation model. At the same time, the structure of PyC crystallite was analyzed, it was found that CF surface crystallinity increased after the increasing of the concentration of carbon source, make the degree of order of the crystal structure increased, so that the degree of graphite and La of the CF surface increased.The flexural performance of C/C composites was tested and the effect of carbon felt density on C/C composite bending strength was compared, The fracture characteristics of materials were analyzed by the stress displacement curve, fracture morphology of the composites was observed by scanning electron microscope and mechanism was analyzed.Carbon source gas C2H2 is molecule of high thermal stability, the initial reaction of acetylene can not occur cracking reaction, but the polymerization reaction, C4 components were formed, and and then benzene and styrene molecules were generated. The important influence factor of Preparation of C/C composites by ECVD is temperature, in addition to the residence time increases under normal pressure, easy to form the soot and lend to crust, close the gap.appropriate to reduce the retention time is conducive to the overall improvement of density.