纤维种类对炭/炭复合材料微观结构和力学性能的影响

摘要

Two carbonized oxidized polyacrylonitrile fiber ( OPF) felts and one polyacrylonitrile¯based carbon fiber ( CF) felt were used as preforms to prepare two kinds of carbon/carbon composites by chemical vapor infiltration,and the effect of fiber type on the microstructure and mechanical properties of the composites were investigated. The microstructure was characterized bypolar¯ ized light microscopy and Raman spectroscopy and the mechanical properties were characterized by nanoindentation and three¯point bend tests. The two carbonized OPFs are surrounded by a darklaminar layer about 1. 4¯2. 6 μm thick followed by a rough laminar layer of about 10. 2¯11. 6 μm, while the CFs are surrounded by a smooth laminar layer about 8. 8μm thick and arough laminar layer of about 4. 4 μm. Nanoindentation indicates that the modulus and hardness of the carbonized OPFsare obviously lower than those of the CFs, and the modulus and hardness of the matrix decrease with increasing extinction angle. The low modulus of the matrix and the OPFsresult in a decrease of the tensile and flexural strength by about 14. 5%¯24. 2% and 7. 3%¯15. 4% and a decrease of the tensile and flexural modulus by about 9. 7%¯19. 8% and 15. 1%¯18. 6%, respectively, for the OPF¯derived composites compared with the CF¯derived composites. However, for the OPF¯derived composites the ductility factor increases by about 224%¯235% be¯ cause of the high content of rough laminarcarbon and the obvious shrinkage of the OPFs after graphitization. Meanwhile, a modelin¯ volving the three components in the composites is proposed to predict their tensile modulus, which shows deviations between experi¯ mental and predicted results below 9. 9%.%采用6K的预氧丝和炭纤维制备预制体，通过化学气相渗积制备炭/炭复合材料。通过偏光显微镜、拉曼光谱、纳米硬度和三点弯曲等手段研究其微观结构和力学性能。结果表明，预氧丝复合材料的基体为暗层和粗糙层炭，厚度分别为1.4¯2.6μm和10.2¯11.6μm；而炭纤维复合材料的基体为光滑层和粗糙层炭，厚度分别为8μm和4.4μm；预氧丝纤维的模量和硬度明显小于炭纤维，同时基体的模量和硬度随消光角的增加而降低；低模量的基体和纤维导致预氧丝复合材料的拉伸强度、拉伸模量、弯曲强度和模量分别降低了14.5%¯24.2%、9.7%¯19.8%、7.3%¯15.4%和15.1%¯18.6%；但其韧性指数却提高了224%¯235%，这是高含量的粗糙层炭和纤维的石墨化收缩所致；同时提出了一个三单元复合模型用来模拟复合材料的拉伸模量，模拟误差小于9.9%。