【摘要】 利用催化化学气相沉积工艺在炭纤维(Cf)表面原位生长碳纳米管(CNT),经聚合物浸渍-热解(PIP)致密化后制备了CNT强化的Cf/Si C复合材料.结合微米压痕和纳米压痕测试方法在微米、纳米尺度研究了CNT强化的Cf/SiC复合材料界面、微区基体以及纤维-CNT-基体组元区域的力学响应机制.结果表明,CNT生长点具有较高的结合强度,界面脱黏出现在纤维/热解碳界面处,原位生长的CNT显著强化了纤维-基体界面结合强度.PIP工艺对CNT造成损伤,致使CNT强化的微区基体的模量和硬度下降,而CNT的拔出、裂纹桥连等行为阻碍了微区基体的裂纹扩展,进而提高了微区基体的破坏容忍度.理论计算结果显示,由CNT带来的韧性贡献约为310.8 J/m2.界面强化效应和微区基体裂纹扩展阻碍效应使纤维-CNT-基体组元的抗损伤能力得到了提高.利用微纳米测试连用手段可深入了解多级增强复合材料的纳米效应.此外,理论计算表明,CNT/基体的界面修饰及对CNT的有效保护会进一步提高CNT对微区基体的韧化效果.更多还原

【Abstract】 Carbon nanotubes(CNT) were grown on a carbon fiber surface via a chemical vapor deposition method, and a CNT reinforced Cf/Si C composite was fabricated via a polymer impregnation and pyrolysis process. In this work, we studied the mechanical properties of microscale areas, such as fiber-matrix interfaces modified by CNT, CNT reinforced matrices, and fiber-CNT-matrices in CNT reinforced Cf/Si C hybrid composites. A combination of Vickers indentation and nanoindentation techniques was adopted to elucidate the relationship between the microscopic and macroscopic mechanical properties of the composites. Nanoindentation was used to test the interfacial bonding strength between the fiber and matrix and the hardness of matrices with embedded CNTs. Vickers indentation was used to study the failure behavior of fiber-CNT-matrix units. Interfacial bonding strength was found to be obviously improved by the presence of in situ grown CNTs. Interfacial debonding occurred at the fiber/pyrolytic carbon interphase but not the pyrolytic carbon/CNT interface, indicating that the interface where CNTs were grown possessed a higher bonding strength. Unfortunately, the nanohardness and modulus of the CNT reinforced matrix(Hv=7.5±1.2 GPa, E=62±5.0 GPa) was lower than that of the matrix without CNT(Hv=11.4±0.3 GPa, E=88.0±1.8 GPa). High resolution transmission electron microscope(TEM) images of the CNT/matrix interface showed that the graphitic structure of the CNT wall was likely damaged. This damage of the CNTs and the resulting reduced matrix properties were thought to be caused by serious chemical reaction between CNTs and the Si-C-O amorphous matrix. Vickers indentation measurements were used to determine the combined properties of fiber-CNT-matrix unit. Because whole Vickers indentations were not as clear as those for the pure ceramic, the exact Vickers hardness was not obtained. The indentation size was used to evaluate the damage resistance of the fiber-CNT-matrix unit. Surprisingly, the indentations in the composite with CNTs were smaller than those in composite without CNTs, indicating that the damage resistance of the whole fiber bundle was improved by CNT addition. Thus, the improved fiber/matrix interfacial bonding strength offset the negative effect of the decreased matrix properties. In addition, the damaged CNT-reinforced matrix remained integrated, while the matrix without CNTs showed a crushed morphology. The cracks were bridged by CNTs, and pull-out of CNTs in the cracks were considered responsible for the improved damage tolerance. The increases in debonding toughness and pull-out toughness caused by the CNTs were theoretically calculated. The simulation indicated that the toughening effect of the CNTs may be further improved if the CNT/matrix interface is suitably tailored and the CNTs are well protected.更多还原