采用液相浸渍-炭化和CVI复合工艺, 制备出在炭纤维和热解炭之间具有中间相沥青过渡层的炭/炭复合材料, 借助偏光显微镜、扫描电镜、透射电镜以及力学性能测试研究了所制备的炭/炭复合材料的微观结构与力学性能. 结果表明: 在偏光显微镜下中间相沥青炭的光学活性高于热解炭的光学活性, 中间相沥青炭在SEM和TEM下均呈片层条带状结构, 热解炭在SEM下呈“皱褶状”片层结构, 在TEM下为粒状结构; 在HRTEM下, 中间相沥青炭、热解炭和炭纤维的晶化程度依次降低. 在加载过程中, 材料内部多层次的界面通过改变裂纹扩展路径而延缓其扩展速度, 在断口形貌上体现出锯齿状的断裂形式, 纤维拔出长度适中, 材料表现出韧性破坏的断裂特征. 材料具有较高的力学性能, 抗弯强度达到244MPa, 断裂韧性达到9.7MPa·m1/2.
Carbon/carbon (C/C) composites, with a mesophase pitch transition layer between carbon fiber and pyrocarbon, were prepared by two step technique of liquid impregnation-carbonization and chemical vapor infiltration (CVI). The microstructure and mechanical properties of the as-obtained composites were studied by polarized light microscope (PLM), scanning electron microscope (SEM), conventional and high resolution transmission electron microscope (TEM, HRTEM) and mechanical properties tests, respectively. Results show that the mesophase pitch carbon exhibits lamellar structure, while the pyrocarbon exhibits like-crinkle lamellar structure under SEM and the granular structure under TEM. Under HRTEM, the degree of alignment of lattice fringes decreases gradually for mesophase pitch carbon, pyrocarbon and carbon fiber. The non-brittle fracture behavior of the composites is related to multiple crack deflections caused by the multi-interface and micro-cracks within the matrix carbon layer. The flexural strength and the fracture toughness (KIC) of C/C composites are 244MPa and 9.7MPa·m1/2, respectively.
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