微观组织结构对C/C复合材料力学行为的影响

采用快速化学液相气化渗透法制备了2D-C/C复合材料,沉积温度为1200-1250℃, 系统压力约0.1MPa.利用偏光显微镜及扫描电子显微镜观察了不同沉积温度制备的基体热解碳的微观组织结构及断口形貌.实验结果表明,1200℃沉积的基体热解碳中粗糙层组织占大多数,其弯曲强度较高、韧性较低; 1250℃的基体热解碳呈现为光学各向异性程度不同的光滑层/粗糙层交替层状组织,其弯曲强度较低、韧性较高,具有非脆性断裂行为.不同微观结构的材料具有不同的强度及断裂模式,除了纤维/基体间界面结合强度不同外,不同温度沉积得到的热解碳微观结构的不同引起裂纹在不同微观结构碳层内的扩展阻力也会不同.此外,裂纹在光滑层/粗糙层界面处的偏转会导致断裂面的高低不平,从而使后者韧性增强.

Influence of Matrix Microstructures on Mechanical Behavior of C/C Composites

C/C composites were fabricated by a rapid chemical liquid-vaporized infiltration (CLVI) process. The deposition temperatures were in the range of 1200--1250℃. The microstructures of pyrolytic carbon and the morphologies of fractured surfaces were observed by polarized light microscope (PLM) and scanning electron microscope (SEM). The influence of matrix microstructures on flexural strength and fracture mode of C/C composites was analyzed. The results show that rough laminar pyrocarbon constitutes the majority of the matrix deposited at 1200℃, which results in higher flexural strength and lower fracture toughness. While the matrix pyrocarbon deposited at 1250℃ displays an alternative layered structure with different optical reflectance, which brings about lower flexural strength and higher fracture toughness. Different mechanical behaviors may be caused by dissimilar spreading resistance of cracks along the interfaces between pyrocarbon laminae with distinct microstructures, and the deflection of cracks along the interfaces between smooth laminar and rough laminar pyrocarbon. In addition, a schematic drawing of fracture profiles of 2D-C/C composites was suggested to explain the fracture mechanism.