Densification and Texture Control in Carbon Fiber/Carbon Composites by Pressure Carbonization

利用加压碳化技术，研究了碳纤维/碳复合材料(C/C复合材料)中基体致密化和织构控制的工艺。本工作包括三个部分：(1)工业C/C复合材料中裂纹扩展的研究；(2)压力对沥青与酚醛树脂相互作用的影响及其产物碳织构的研究；(3)用两种不同的前驱体和压力碳化法制备C/C复合材料的初步生产。结果表明，C/C复合材料的基体织构决定了其力学性能。研究表明，良好的基体马赛克织构对于减缓C/C复合材料的裂纹扩展和获得高韧性是必不可少的。在沥青中掺入聚对苯二甲酸乙二醇酯(PET)或酚醛树脂可以控制C/C复合材料中光学单元的大小。随着添加剂(PET或酚醛树脂)用量的增加，基质的织构由粗马赛克不断向各向同性转变，由中细马赛克织构转变为中细马赛克织构。这两种前驱体之间的相互作用在压力下被加速，得到了均匀的光学织构的基体。在目前的工作中，由于所用高压釜的尺寸有限，且难以重复前驱体浸渍，无法获得足够高密度和大尺寸的复合材料来研究其断裂行为。然而，通过两种不同的前驱体混合和加压碳化，我们可以证实碳纤维/碳复合材料获得高密度和控制基体织构的可能性。

By using pressure carbonization technique, the processes for densification and texture control of the matrix in carbon fiber/carbon composites (C/C composites) were investigated. The present work consisted of three parts; (1) the study on crack propagation in the matrix of a commercial C/C composite, (2) the study on the pressure effect on the interaction between pitch and phenol resin, and also on the texture of resultant carbons, and (3) the preliminary production of C/C composites by using two different precursors and by pressure carbonization.The crack propagation in a C/C composite was observed under polarized liaht microscope. The texture of the matrix of C/C composite was shown to govern its mechanical properties. A fine mosaic texture of the matrix was suggested to be essential for slowing down the propagation of deteriorative crack and for getting high toughness of the C/C composite.The size of optica units in the matrix of C/C composites was found to be controlled by mixing either polyethylene terephthalate(PET) or phenol resin into pitch. With increasing the amount of additives (PET or phenol resin), the texture of the matrix changed continuously from coarse mosaic to isotropic through medium and fine mosaic textures. The interaction between these two precursors was accelerated under pressure and the matrix with homogeneous optical texture was obtained.In the present work, we could not have the composites with sufficiently high density and large size for studying on their fracture behavior because of the limited size of the autoclave used and the difficulty of repeated precursor impregnation. However, we could confirm the possibility for carbon fiber/carbon composite to get high density and also to control the texture of the matrix by mixing two different precursors and by carbonization under pressure.