- مبلغ: ۸۶,۰۰۰ تومان
- مبلغ: ۹۱,۰۰۰ تومان
Different contents of carbon nanotubes (CNTs) were in situ grown on the surface of carbon fiber bundles by injection chemical vapor deposition. The fibers were then stacked into unidirectional preforms and densified by pyrocarbon (PyC) via chemical vapor infiltration. The effects of CNT on the strength and toughness of carbon/carbon composites (C/Cs) before and after heat treatment at 2100℃ were investigated. Results show that both the tensile strength and work of fracture achieves the optimum performance when the CNT content is 1.5 wt%. After heat treatment, the tensile strength increases by 25.68% for CNT reinforced C/Cs (CNTs-C/Cs), while only 4.36% for pure C/Cs. The refinement effect of CNT promotes the resistance of PyC matrix against destruction and makes it maintain the structural integrity and continuity even after heat treatment. Before heat treatment, the presence of CNT results in a decreased in-plane lattice size (La) compared with pure C/Cs. while interestingly, after heat treatment, La becomes larger due to the stress graphitization of CNT. The stress graphitization induced by CNT gives the carbon matrix a stronger ability to resist crack propagation, thereby enhancing the strength of the C/Cs. In addition, the existence of CNT changes the fracture mode of the C/Cs and increases the way of energy consumption during the tensile test. Thus, both fibers and the interface of the composites are fully utilized.
In this work, the tensile strength of CNTs-C/Cs increased by 14.2% and 30.5% for the CNT contents of 0.9 wt% and 1.5 wt%, respectively, with which decreased by 18.3% for 2.4 wt%. The work of fracture and Young’s modulus as well as tensile strength achieved optimum performance when CNT content was 1.5 wt%. It was found that the presence of CNT not only changed the microstructure of PyC to maintain an anti-destructive matrix of C/Cs but changed the fracture mode of tensile tests to strengthen and toughen the C/Cs. After heat treatment, the tensile strength of CNTs-C/Cs increased by 25.68%, much higher than 4.36% of pure C/Cs, indicating that heat treatment promoted the strengthening and toughening effect of CNT. The La value of CNTs-C/Cs increased rapidly from 3.08 nm to 4.49 nm, further enhancing the in-plane tensile strength of PyC. The larger La and the step-like fracture morphology enabled HT-CNTs-C/Cs to have the highest strength among the four kinds of composites. The existence of CNTs not only improved the microstructure of PyC and enhanced the ability of CNTs-C/Cs against destruction, but also opened a new way of energy consumption, thus the fibers and the interface being fully utilized. Heat treatment strengthened the influence of CNTs on the properties of the composites. The suggested mechanism of CNTs in strengthening and toughening the C/Cs provides a guidance for the preparation of C/Cs of high strength and high toughness.