微正压ICVI制备C/C复合材料及其结构与性能研究

【作者】 刘立海；

【导师】 黄启忠；

【作者基本信息】 中南大学 ， 材料学， 2008， 硕士

【摘要】 针对炭/炭复合材料的应用背景,以缩短材料的制备周期、降低成本为目的,本文工作采用微正压等温化学气相渗透工艺制备C/C复合材料。系统地研究了碳源气体浓度、碳源气体种类、沉积温度、气体滞留时间、毡体初始密度、反应容器空间等工艺条件对C/C复合材料增密速度、微观结构的影响。发现减小反应气体在反应容器内的自由流动空间对炭/炭复合材料的致密化有较为显著的影响,采用石油液化气作为碳源气体,氮气作为载气,沉积温度830～950℃,沉积35h可将60mm×20mm×10mm的预制体增密至1.73g/cm~3,总炭收率达32%。采用偏光显微镜、扫描电镜、X—射线衍射仪等手段对热解炭的微观组织结构、沉积表面形貌以及石墨化度进行了研究,结果表明热解炭结构均为中等织构热解炭且石墨化度随沉积温度的升高有明显的增大趋势,材料经2300℃,2h高温石墨化处理后发现在1000℃沉积的样品石墨化度为32.5%,在1100℃达到55.5%。采用本文工艺材料的增密速度和炭收率与负压等温化学气相渗透工艺相比较,均有较大幅度的提高。而且本文工艺无需机械泵抽真空,也不需要循环冷却水,降低了材料的制备成本。对材料的力学性能进行了测试,探讨了影响材料抗弯强度的主要因素以及材料的弯曲破坏机理。结果表明:实验制备的二维C/C复合材料在垂直方向的抗弯强度为20～68MPa。随着炭纤维和热解炭含量的增加,C/C复合材料的抗弯强度也随之增大。C/C复合材料的弯曲破坏属于脆性断裂,微观破坏行为主要表现为由于纤维与热解炭结合强度较强,当施加载荷超过材料的最大承受能力时,基体炭与纤维几乎同时断裂,只有少许纤维从基体炭中拔出且长度很短。更多还原

【Abstract】 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.更多还原