炭纤维和炭/炭复合材料显微结构与性能研究

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	炭纤维和炭/炭复合材料显微结构与性能研究
	周庚衡
学位类型	博士
导师	叶恒强 ; 贺连龙
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料物理与化学
关键词	炭纤维炭/炭复合材料透射电镜微观结构 Carbon Fiber Carbon/carbon Composites Tem Microstructure
摘要	"炭/炭复合材料具有高强度、低密度、耐高温以及耐磨损等优良的性能，在航空航天和国防军事等领域有着独特的应用。本论文通过高分辨透射电子显微术、选区电子衍射等手段，研究了炭/炭复合材料中炭纤维的微观结构及其随高温热处理的演化规律；采用高分辨和原位形变观察分析了各种炭/炭复合材料的界面结构及性能。研究结果主要包括以下几点： 1. 炭/炭复合材料中炭纤维的微观结构表征首次将选区电子衍射所获得的取向角用于定量描述炭纤维中碳原子面沿炭纤维轴向择优取向程度，并确立采用炭纤维纵轴截面上的连续选区电子衍射方法获得取向角的连续变化曲线来分析炭纤维内原子面的择优取向均匀度，揭释炭纤维的皮芯结构本质为皮芯位置处碳原子面择优取向度存在较大差异。此外，还通过这种方法，定量研究了炭/炭复合材料中炭纤维内碳原子面随热处理温度的变化规律：随着热处理温度的升高，炭纤维内原子面变得逐渐趋于平行于炭纤维轴向，这种变化首先发生在炭纤维的表层，接着炭纤维芯部的碳原子面也变得趋于平行于炭纤维轴向；高分辨观察表明，随着热处理温度的增加，炭纤维内微晶的尺寸逐渐增大，并形成纳米尺度的孔隙。 2. 炭/炭复合材料界面结构及性能研究在化学气相渗制备的炭/炭复合材料中发现三种不同界面类型：热解炭结构突变型界面，热解炭结构渐变型界面及热解炭结构交替变换型界面；同时发现低织构热解炭层内微裂纹较少，高织构热解炭内存在大量纳米尺度的微裂纹；低织构热解炭与高织构热解炭之间存在约20nm厚的过渡区域。化学气相渗和树脂浸渍混合工艺制备的炭/炭复合材料中树脂炭和热解炭的界面结合较差，界面处有大量裂纹存在。浸渍剂沥青浸渍法制备的炭/炭复合材料中沥青炭与炭纤维界面结合良好，沥青炭具有高度石墨化结构，沥青炭呈层状结构，其内部存在大量的微裂纹；在纤维束之间的大孔隙内喹啉不溶物的炭化产物会聚集成团后被高度石墨化沥青炭包裹。原位观察表明炭纤维表面的沟槽结构对界面力学性能具有较大影响，当外加载荷较小时界面会发生单个沟槽解离，当外加载荷较大时会发生多个沟槽同时解离；热解炭层间的纳米条带能阻碍微裂纹的聚集、长大和扩展，使得热解炭具有良好的形变回复能力。 3. X射线对于精确测量炭/炭复合材料微观结构参数实用性探讨透射电子显微镜的观察结果与X射线实验对比分析表明，热解炭围绕炭纤维同心层状沉积的特殊织构结构强烈影响X射线衍射模式，进而使得X射线所测量的炭/炭复合材料中的热解炭的微观结构参数在不同的方向上具有不同的数值；当使用X射线测量炭/炭复合材料中热解炭的微观结构参数时，低石墨化度的炭纤维使其衍射峰不对称进而给微观结构参数测量带来误差，因此透射电镜的观察对于炭/炭复合材料中热解炭的微观结构分析不可或缺。"
其他摘要	" Due to their high strength, low density, endurance of high temperature and abrasion properties, carbon/carbon composites have unique applications in the fields of aerospace and national defense industries. In this dissertation, the microstructure of carbon fiber in the carbon/carbon composites and its evolution with high temperature treatment were investigated by means of high resolution transmission electron microscopy (HRTEM), selected area electron diffraction and X-ray energy dispersive spectroscopy. Furthermore, different types of interfaces and their properties were investigated by HRTEM and in-situ TEM observations. The main results are listed as follows: 1. Microstructure characterization of carbon fiber in carbon/carbon composites The orientation angle (OA), measured from selected area electron diffraction patterns, was used to description the preferred degree of basal planes parallel to the fiber axis on the longitudinal section for the first time. The distribution of the orientation of basal planes in the carbon fiber can be investigated by statistic OAs of a carbon fiber on the longitudinal section. It shows that the essence of the difference between the core and skin of carbon fiber is the preferred degree of basal planes parallel to the fiber axis. In addition, the evolution of the preferred degree of orientation of basal planes with high temperature treatment was quantitatively studied. It shows that the preferred degree of orientation of basal planes decreases gradually from the skin region to the core region after heat treated at 1000 ℃. With increasing heat-treatment temperature, the basal planes change parallel to the fiber axis, first in the skin region and then in the core region. Moreover, HRTEM observations reveal that the crystallite size increases with the increasing heat treatment temperature and pores of nanometer scale start to form in the fiber. 2. Microstructure and properties of interfacial structure of carbon/carbon composites Three types of interface were observed in the carbon/carbon composites fabricated by cheical vapor infiltration: the type of pyrocarbon changes abruptly or gradually or alternately of these two types at the interface. Meanwhile, it shows that there is not any microcrack in the low-textured pyrocarbon, and many microcracks in the high-textured pyrocarbon. A transition layer with 20nm in thickness was observed between the lwo and high-textured pyrocarbon. The interface between the pyrocarbon and resin carbon is weakly bonded with many cracks in the carbon/carbon composites fabricated by chemical vapor infiltration and resin soakage. However, the interface between carbon fiber and pitch carbon is well bonded in the carbon/carbon composites fabricated by soakage of impregnant pitch. The pitch carbon contains well graphitized layers with many microcracks. In addition, quinoline insoluble particles aggregate at the void between the fiber bundles and then wraped by layered structure pitch carbon. In-situ force measurements indicates that the surface of a carbon fiber has groove-like features, which give rise to strong bonding between the fiber and the pyrocarbon matrix. When a small force is exerted perpendicular to the transverse section of the carbon fiber, the interface between the fiber and the pyrocarbon matrix debonds by loosening of individual grooves. Many grooves debond when the force is large enough. In addition, both low-textured and high-textured pyrocarbon possess good deformation properties. The delamination of the multi-layers to form nano-cracks is the energy-dissipation mechanism contributing to the recovery of the pyrocarbon matrix after deformation. 3. The interpretation of X-ray diffraction from the pyrocarbon in carbon/carbon composites with comparison of TEM observations Comparison of TEM and XRD investigations of C/C composites points out that the XRD patterns were influenced by the carbon fiber, amount of different types of pyrocarbon and the orientation of basal planes in the concentric layered pyrocarbon. These factors have different influence on the XRD patterns. Due to the influence of the orientation of basal planes in the pyrocarbon, the structural parameters of the high-textured pyrocarbon in the same composites are different when measured from different directions. It can be concluded that XRD measurements on the C/C composites should be interpreted with great caution. TEM observations for detailed microstructure analysis of C/C composites are important and can be complements to the XRD measurements."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64439
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	周庚衡. 炭纤维和炭/炭复合材料显微结构与性能研究[D]. 北京. 中国科学院金属研究所,2012.