【作者】 王玉泉；

【导师】 邓海金；

【作者基本信息】 清华大学 ， 材料科学与工程， 2004， 硕士

【摘要】 在炭/炭复合材料的致密化过程中,由于预成型体内沉积工艺参数的波动性很大,使其结构具有多样性,这种多样性表现出丰富多采的微观形貌及特征,不同的结构所对应的材料性能差异也很大。只有搞清这些结构的分类、形貌特征、性能和产生的条件,才能够深入地理解炭/炭复合材料工艺-结构-性能三者的联系,从而合理地控制工艺参数,制备出具有所需结构及性能的材料。本文采用光学(普通、偏光)显微镜、X-射线衍射、扫描电子显微镜(SEM)、高分辨透射电子显微镜(HRTEM)等研究方法,对化学气相沉积(CVD)C/C复合材料的不同样品的显微组织和精细结构进行了较深入的研究。通过X射线衍射测定了不同样品的石墨化度,得到了石墨化度与样品微晶尺寸大小的关系。在炭布预制体C/C复合材料中,石墨化度g随着石墨化处理温度的变化分为三个区间,低于2600℃和高于2800℃时,g随石墨化处理温度的增高迅速增大,而石墨化处理温度在2600℃-2800℃之间时,g变化很小。利用正交偏振光的基本原理测量了沉积炭消光角(Ae),分析了沉积炭的偏光下的形貌,得出随着消光角的增加,在偏光显微镜下的形貌更为粗糙,更富有层次感。石墨化度较高的C/C复合材料的沉积炭的消光角较大,石墨化程度较低的消光角较小。其主要原因是,石墨化程度较高时,粗糙层片状组织层平面更加完整,各向异性更大。通过透射电镜的晶格像分析了不同样品的炭纤维的精细结构,并采用石墨化度高的Dunlop试样的炭纤维微晶的完整层面距来标定了Goodrich和炭布预制体C/C复合材料的炭纤维的层面距。结果表明,在不同热处理温度下炭布预制体C/C复合材料的微晶层间距随石墨化温度的升高,层间距变小。 通过透射电镜和选区电子衍射,研究了不同样品中基体炭的精细结构。观察到在石墨化度高的Dunlop试样和石墨化处理温度高的炭布预制体C/C复合材料中,微晶颗粒尺寸较大,而石墨化度低的Goodrich试样和石墨化处理温度低炭布预制体C/C复合材料中,微晶颗粒尺寸较小或者以粒状小颗粒为主。通过选区电子衍射可以标定沉积炭的取向角,发现随着石墨化程度的升高,取向角会增大,从而进一步得到了取向角和消光角之间的关系。更多还原

【Abstract】 During the compacting process of Carbon/Carbon materials, different structures will apper due to the change of parameters of deposition technics. Different structures result in different properties. Only by comprehending the classification, characteristic, properties and technical conditions, could we know the relationship among the structures, properties and technics. The process parameters can then be determined and controlled properly, after which we can get the stuctures and the relative properties needed.The present work had analyzed the microstructures and fine structures of pyrocarbon and carbon fiber in the C/C composites in detail by means of polarized light microscopy, XRD, SEM and HRTEM.The graphitization degree of several samples were analyzed by x-ray diffractions. With the graphitization temperature rises, the graphitization of cloth precursor C/C composites have been divided into three stages. Below 2600℃ and above 2800℃, the graphitization degree increases rapidly with the increase of temperature. While from 2600℃ and 2800℃, the graphitization degree changes little.The basic principles of polarized light microscopy observation were used for measuring the extinction angles (Ae). Pyrocarbon may be classified according to the extinction angles. Under the polarized light microscopy, the structures can be more rough with the increase of extinction angles. The main reason is that the rough laminar with higher graphitization degree have more complete layer planes and more anisotropic. The microstructures of carbon fibers in C/C composites had been analyzed with the fringe lattices of TEM. The structure of Dunlop sample was looked on as the exact graphic layer plane, the structures of Goodrich and cloth precursor C/C composites can be measured. In the cloth precursor C/C composites, which have the same compacting technics, the layer spaces will decrease with the increase of graphitization degrees. The fine structures of pyrocarbons have been analyzed with TEM and SAED, the relative speed of pyrogenation, nucleation and the growth decides the structure of pyrocarbons.The orientation angles (OA) were measured by SAED.更多还原