Slight Positive Pressure Icvi Preparation Of C, / C Composites And Their Structure And Properties Of Study

With the application background of carbon/carbon composites and the purpose of cutting down the preparing cycle and cost, micro-positive pressure isothermal chemical vapor infiltration was studied and employed for fabricating C/C composites. The influences of infiltration conditions (including the concentration of hydrocarbon gas, different hydrocarbon gas, deposition temperature, hydrocarbon gas residence time, preform initial density, reaction container space ) on the densification behavior and microstructure of pyrocarbon have been systematically investigated. The results shown that, with micro-positive isothermal chemical vapor infiltration furnace, reducing the free flowing space of reaction gas has greatly effected on the densification of C/C composites, using the liquefied petroleum gas as hydrocarbon gas and nitrogen gas as dilute gas, the porous preforms, 60mm×20mm×10mm, with the density of more than 1.73g/cm~3 are obtained in 35 hours at deposition temperature from 830℃to 950℃, the carbon yield reached 32%. The microstructure, deposition surface morphology and graphitization degree of pyrocarbon in C/C composites were analyzed by PLM, SEM, and XRD respectively. The studies shown that the medium-texture was mainly obtained by PLM, the graphitization degree of C/C composites has obvious improved with the enhancing of deposition temperature, the researchs shown that the graphitization degree was 32.5% at 1000℃, however it reached 55.5% at 1100℃after 2300℃, 2 hours high temperature heat treatment. The studies of experiments shown that the rate of densification and carbon yield have been improved greatly compared with negative-pressure isothermal chemical vapor infiltration, and this craft didn't need atmospheric pump and cooling water circulation for reducing the preparing cost of C/C composites.Mechanical performance of C/C composites are also tested, and the influencing factors of them are discussed. The results shown that the flexural strength of 2D C/C composites has a value of 20～68MPa in perpendicular direction. The flexural strength of C/C composites has improved with the content of carbon fibers and pyrocarbon increasing. The flexural failure of C/C composites is brittle fracture, the micro-fracture mechanisms are shown as the intensity of combining carbon fibers with pyrocarbon was strong tightly, when the enforcing load exceeded the maximum support load limit of C/C composites, pyrocarbon and carbon fibers nearly simultaneous fractured and only a little carbon fibers have been pulled out and the pulled out length was very short.