【作者】 徐进；

【导师】 周仲荣；

【作者基本信息】 西南交通大学 ， 机械设计及理论， 2003， 博士

【摘要】 微动损伤普遍存在于航空航天、核反应堆、电力电子、交通运输工具和人工植入器件等工程领域的关键零部件中，随着高技术领域对高精度、长寿命和高可靠性的要求，微动损伤的危害日益凸现。固体润滑涂层作为抗微动损伤的主要防护措施之一，已在工程领域得到了广泛应用，但尚未见到有关固体润滑涂层抗微动磨损特性与机理深入系统的研究。 本文在高精度液压式微动磨损试验机上，采用球/平面接触模式，在不同载荷和位移振幅条件下，对基材（调质42CrMo钢）和4种固体润滑涂层（粘结MoS₂涂层、粘结石墨涂层、粘结聚四氟乙烯（PTFE）涂层和电刷镀Pb涂层）进行了微动磨损试验。在动力学分析基础上，利用表面轮廓仪、激光共焦扫描显微镜（LCSM）、扫描电子显微镜（SEM）、电子能谱仪（EDX）、x射线光电子能谱（XPS）、x衍射分析（XRD）、傅立叶红外光谱仪和划痕测试仪等材料表面分析测试设备，系统研究了不同固体润滑涂层的微动摩擦特性和磨损行为，建立了微动磨损的物理模型。针对16V280型柴油机连杆齿型结合面的微动损伤，通过表面工程设计，成功地应用固体润滑涂层减缓了微动损伤。本研究取得的主要结果和结论如下： 1、粘结MoS₂涂层微动摩擦特性强烈地依赖于位移幅值、法向载荷和循环次数，微动运行于部分滑移区和滑移区，混合区消失。按摩擦系数随循环次数的变化可将其磨损行为划分为三个阶段：即（a）磨损的初期，表面转移膜与表面塑性流动层在两接触副之间形成，摩擦发生在MoS₂晶体的滑移面间，摩擦系数较低，XRD分析结果表明在塑性流动层形成的再结晶过程中，具有明显的择优取向；（b）随循环次数增加，在反复疲劳应力作用下塑性流动层发生加工硬化和氧化，润滑作用下降，摩擦系数上升，并可观察到龟裂现象；同时，微裂纹沿滑移面（平行于表面）间扩展，并逐步相互贯通，导致涂层呈片层状剥落；（c）颗粒严重脱落，磨损率增加，中心区大面积基体裸露出来，表面严重损伤，摩擦系数达到基体材料稳定阶段的数值，涂层失去保护作用。粘结石墨涂层的微动磨损特性与MoS₂涂层相似。 2、系统研究了MoS₂粘结涂层制备工艺（基体材料、涂层厚度、固化温度和表面粗糙度）、环境因素（湿度、温度和润滑油介质）对涂层微动磨损寿命的影响。结果表明，选择较硬基体、增加涂层厚度、对基体表面进行表面第11页 西南交通大学博士研究生学位论文喷砂预处理以及对涂层进行高温固化均有利于提高涂层的微动磨损寿命，其中固化温度对涂层磨损寿命的影响最为显著。随着位移幅值的减小，微动趋向于部分滑移区，上述因素的影响更显著；环境湿度增加，加剧涂层在磨损过程中的氧化，磨损寿命降低，在高位移幅值条件下更明显；温度对磨损寿命有重要影响；在滑移区，加润滑油的混合润滑大大降低了磨损寿命，但是，在较低位移和较高载荷条件下，混合润滑却表现出良好的润滑性能。 3、粘结PTFE涂层的微动摩擦磨损性能取决于载荷的变化，存在一个临界载荷，当低于临界载荷时，摩擦系数随载荷的增加而减小，磨损率几乎不变，当高于临界载荷时，摩擦系数随载荷增加而增加，磨损率急剧增加。涂层微动损伤主要表现为分子链承受过大应力而断裂，长时间承受交变疲劳应力作用导致微裂纹的萌生和扩展，涂层呈剥落破坏。润滑油与PTFE涂层的混合润滑可以在比较宽的载荷范围内表现出良好的减摩性能。 4、电刷镀的涂层的摩擦系数随位移幅值或循环次数的增加而有所增加，三个微动区域均可观察到。在部分滑移区，表面损伤轻微；进入混合区域，在早期阶段，由于涂层的润滑作用，接触表面处于相对滑移状态，随着循环次数的增加，涂层逐渐丧失润滑效果，相对运动趋向于部分滑移；在滑移区，涂层磨损早期有明显塑性流动特征，涂层破坏表现为按剥层机制呈片状剥落。 5、润滑涂层改变了42CrMo钢基材的微动特性，MoS。、石墨、PTFE涂层的混合区消失，电刷镀N涂层的微动区域左移。比较不同涂层的磨损机制发现，MOS。、PTFE和 Ph涂层在磨损过程中发生了摩擦化学作用，导致涂层氧化，其润滑性能逐渐丧失。四种涂层的微动磨损主要表现为：在往复疲劳应力作用下裂纹萌生和扩展，按剥层机制呈层状剥落。采用极坐标法综合比较了涂层的机械和微动磨损性能，结果显示，MOS。涂层综合抗微动磨损性能最佳，然后依次是PTFE涂层、石墨涂层和 Ph涂层。 6、在对16VZSO型柴油机连杆齿型结合面失效分析、动力学、接触应力及相对位移分析的基础上，认为齿面裂纹的产生归因于齿面间的微动疲劳作用。通过表面工程设计，选用MoS。粘结涂层可以减缓齿面的微动损伤。现已装车进行实际考察，目前运行状况良好。更多还原

【Abstract】 Fretting may occur in many engineering key structures, such as space mechanisms, nuclear power plants, electrical equipments, and even orthopaedic implants. Fretting may result in two kinds of damage: wear and rapid crack nucleation and propagation. Some of the failures initiated by fretting have tragic consequence. Solid lubricant coatings are usually used to mitigate fretting damage. However, their effects on preventing fretting wear behaviors and mechanism have rarely been investigated systemically.Four solid lubricant coatings, i.e. MoSi bonded coating, graphite bonded coating, PTFE bonded coating and Electro-brush Plating Plumbum Coating, together with their substrate material (E4142 steel), have been tested under ball-on-flat contact with various normal loads and displacement amplitudes. Dynamic analyses have been performed to study fretting friction and wear behaviors in detail, and a physical model on fretting wear was built. The result is used to solve the fretting problem of the connecting rods for 16V280 diesel engine. The main research works and results are concluded in the follow:1. Under the fretting condition, only partial slip regime and gross slip regime exist with MoS2 bonded coating. According to the variation of the friction coefficient with the increase of number of cycle, the degradation of the coating is outlined as three stages: (1) During early stage, the transfer film and plastic flow layer form between two contact pairs. Friction occurs between two slip planes of MoSa crystals. XRD show that MoSa crystals exhibit significant orientation during the formation of the plastic flow layer. (2) The plastic flow layer occurs work-hardening and oxidation, which can be identified by the following phenomenon: lubricating effect becomes weak; friction coefficient increases; micro cracks initiate, propagate along sliding planes, and then particles spall in the shape of flake. (3) The wear rate increases rapidly as severe detachment of particles occur at contact center. The coating almost lost its protective effect as a lubricant. The fretting wear performance of bonded graphite coating is similar to that of MoSa bonded coating.Various factors including preparation processes (substrate material, thickness, curing temperature, and surface roughness) and environmental condition (temperature, relative humidity and mixed lubricant with oil) effect on the fretting wear life of MoS2 bonded coating have been investigated. The test results exhibit enhancing substrate hardness, increasing coating thickness, sandblasting substrate surface, and especially heat curing are favorable to extend the wear life of the coating. For all the condition, the wear life increases with decreasing displacement amplitude. It helps to prolong service duration of MoS2 coating by reducing relative humidity, especially at lower displacement amplitudes. The effect of temperature on wear life is marked. With lubricant oil, the wear life reduces with increasing displacement amplitude or decreasing normal load, however, adding oil could be beneficial for improving wear life at quite low displacement amplitudes.2. PTFE bonded coating has excellent anti-friction and wear-resistant performance. Friction and wear characters of the coating depend strongly on normal loads. There is a critical normal load below which the change of wear rate is slight, while above that, severe surface damage is observed. The degradation of the coating on account of mechanical and chemical factors is as follows: the fracture of molecular chains; the nucleation and propagation of micro-cracks, which cause particles detachment in lame shape afterwards. It is favorable to improve PTFE coating protective fretting damage effect by adding oil.3. For electro-brush plating Plumbum coating, three fretting regimes can be observed under fretting condition. In mixed fretting regime, relative micro-silp occurs between contact interfaces in early stage, with increasing the number of cycles, micro-silp occurs at the contact edge as the lubricant更多还原