【作者】 上官倩芡；

【导师】 程先华；

【作者基本信息】 上海交通大学 ， 机械设计及理论， 2007， 博士

【摘要】 聚四氟乙烯(PTFE)以极低的摩擦系数、优异的热稳定性和耐腐蚀性著称,是一种理想的自润滑材料。但是,纯PTFE机械性能差、线膨胀系数大、导热性差,导致其磨损量大,因而不适于单独作耐磨材料使用。碳纤维(CF)具有高比强度、高模量、极佳的抗疲劳和抗蠕变性能,被广泛用于复合材料增强相。由于碳纤维表面呈化学惰性,与树脂基体复合时存在浸润性差、难以形成有效粘结的问题,极大地限制了碳纤维复合材料性能的发挥。针对界面性质是影响复合材料综合性能的关键因素,本论文用稀土对碳纤维进行表面改性,以有效地提高碳纤维与PTFE基体之间的界面结合强度及界面韧性,进而提高碳纤维填充PTFE (CF/PTFE)复合材料的摩擦学性能,取得了原创性的研究结果。第一,分别采用稀土改性剂、空气氧化法对碳纤维进行表面处理,开展了不同表面处理碳纤维填充PTFE复合材料力学性能的测试,确定了稀土改性剂中稀土元素的最佳含量。结果表明:稀土表面处理比空气氧化法更有效地提高了碳纤维与PTFE基体之间的界面结合性能;稀土表面处理CF/PTFE复合材料的界面结合性能主要受其中稀土元素含量的影响,当稀土元素的含量为0.3wt%时,复合材料的力学性能最佳。第二,运用X射线光电子能谱(XPS)分析技术,探讨了碳纤维表面改性作用的机理。结果表明:采用稀土改性剂处理碳纤维,通过稀土与碳的亲和作用导致纤维表面的碳-碳键松弛并活化碳纤维表面,提高了碳纤维表面的含氧官能团数量;稀土元素与碳纤维表面含氧官能团以及PTFE分子之间发生配位化学反应,形成了稀土配位键合,使CF/PTFE复合材料形成强韧性的界面层,从而显著提高了复合材料的力学性能。第三,采用经过不同表面改性处理的碳纤维填充PTFE,制备得到CF/PTFE复合材料,系统研究了复合材料在连续滑动摩擦条件下的摩擦磨损性能。结果表明:在相同试验条件下,稀土表面处理CF/PTFE复合材料比未经表面处理以及空气氧化处理CF/PTFE复合材料具有更优异的摩擦学性能;油润滑使CF/PTFE复合材料的摩擦系数和磨损量比干摩擦时明显降低。第四,在往复滑动摩擦条件下,稀土表面处理所形成的优异强韧性界面层能够抵抗往复载荷形成的冲击,有效地抑制了PTFE的片状剥落和大规模转移,从而降低了CF/PTFE复合材料的摩擦磨损。第五,探讨了稀土表面处理提高CF/PTFE复合材料摩擦学性能的机理。经稀土表面处理后,强韧性的界面层使碳纤维的增强作用得到有效发挥,并提高了复合材料的承载能力。稀土摩擦化学反应促进了PTFE复合材料在对偶件表面转移膜的形成;摩擦化学反应的产物在干摩擦条件下可起到有效润滑作用,油润滑条件下与碳纤维表面的稀土配合物一起成为润滑油添加剂,提高润滑效果。本文基于制备高性能的CF/PTFE复合材料,探讨了稀土改性碳纤维表面的工艺方法以及提高复合材料界面强韧性的机制,深入系统地研究了稀土表面改性对CF/PTFE复合材料力学及摩擦学性能的影响,阐明了其作用机理。发展稀土改性碳纤维增强热塑性复合材料新技术,对于提高CF/PTFE复合材料的工程应用价值、扩大稀土在表面工程领域的应用等方面具有重要意义。更多还原

【Abstract】 Polytetrafluoroethylene (PTFE) is an ideal self-lubricating material which has very low friction coefficient, high thermal stability and chemical stability. But it can not be used as anti-wear material alone because of its poor mechanical properties, bad thermal conductivity and high wear rate. Carbon fibers (CF) are widely used as fillers in composite materials due to their high specific strength, high modulus and high resistance to fatigue and creep. However, their applications have been largely limited because of their chemically inert surfaces, low wettability and interfacial bonding with resin matrix.In order to improve the interfacial adhesion and interfacial toughness between CF and PTFE matrix, rare earths (RE) were used to modify carbon fiber surface in this dissertation, and then, enhance the tribological properties of the CF reinforced PTFE (CF/PTFE) composites. Some significant original results were obtained.Firstly, rare earths modifier and air oxidation treatment were used for the surface modification of carbon fiber, and the effects of these two methods on CF/PTFE composites were comparatively evaluated through tensile strength and bending strength tests. The optimum rare earths content in the rare earths modifier was also discussed. The results showed that RE surface treatment was superior to air oxidation in promoting interfacial adhesion between carbon fiber and PTFE matrix. The interfacial adhesion of the RE surface treated CF/PTFE composites was mainly controlled by the contents of RE, and the optimum mechanical property was obtained when the content of rare earth elements was 0.3 wt%.Secondly, X-ray photoelectron spectroscopy (XPS) was used to analyze the mechanism of fiber surface treatment. The results showed that, with RE surface treatment, the CC bond of carbon fiber was loosed because of the affinities between RE and carbon. Therefore, the surface activity of carbon fiber was improved, and the amount of oxygen-containing functional groups on carbon fiber surfaces was also increased; Coordination chemical reactions occurred among RE, oxygen-containing groups and PTFE molecules, leading to an improvement in the interfacial bonding and toughness of CF/PTFE composite, which accordingly improved the mechanical properties of the composite.Thirdly, CF/PTFE composites were manufactured by incorporating differently surface treated carbon fiber into PTFE resin. The friction and wear behaviors of the composites under continue sliding friction were investigated in detail. The results showed that, under the same experimental conditions, the tribological properties of the PTFE composites filled with rare earth treated carbon fibers were better than those of PTFE composites filled with untreated and air-oxidated carbon fibers. The friction coefficient and wear of the CF/PTFE composites were obviously decreased under oil lubrication condition.Fourthly, under reciprocating sliding condition, the high interfacial bonding and toughness of RE treated CF/PTFE composite effectively resisted the impact caused by applied load. The large-scale transfer and rubbed-off of PTFE were restrained, which reduced the friction and wear of CF/PTFE composite.Fifthly, the improvement mechanism of RE on tribological properties of CF/PTFE composite was discussed. After RE surface treatment, the improved interfacial bonding and toughness advanced the reinforcement of CF and the load-carrying capability of CF/PTFE composite. The RE triochemical reaction promoted the formation of transfer films on the counterface. Under dry sliding condition, the productions of RE triochemical reaction acted as solid lubrication and reduced the friction and wear of the composite; under oil lubrication, these productions and RE complex on CF surfaces became the additives of lubrication oil, and improved the lubricating effect of the oil.Based on the development of high performance CF/PTFE composite, the process of RE surface treatment of carbon fiber and the mechanism of rare earths on interfacial obdurability of CF/PTFE composite were discussed. The effects of RE surface treatment on mechanical and tribological properties of CF/PTFE composite were systematically investigated. Developing the new surface modification technology of carbon fiber with rare earths is very important for improving engineering value of CF/PTFE composites and surface engineering application of rare earths.更多还原