| 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...
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