Research On Preparation And Tribological Properties Of Self-Lubricating Coating By ESD

The self-lubricating coating of Cu-BN whose substrate was45steel was prepared by the technology of electro-spark deposition. The consequent jobs were followed: analyze the physical and chemical compatibility of coating, research the ways how the coating was prepared, simulate the stress of friction via FEM, and explore the surface appearance as well as properties of friction and wear, lubricating mechanisms.Basing on anti-friction and friction-reduced technology, the ingredients of coating and substrate were matched well. Using the calculating methods of thermodynamics, the chemical compatibility was analyzed between the self-lubricating coating of Cu/BN and45steel besides C11/MoS2and YT15, in addition, the stress of single-layer coating was compared with that of multiple-layers coating. Results indicate that the latter was much smaller; the self-lubricating coating of Cu/BN can match45steel well. So45steel was chose as the substrate in the experiment of this thesis.The self-lubricating coating was prepared by the technology of electro-spark deposition. The influence of processing parameters on roughness, friction coefficient and wear loss was also researched on the condition of rotation and vibration respectively. The optimum parameters were as follows:the same deposition time:10min; capacity when vibrating:gear2; capacity when rotation:gear3. Through observing the section and surface appearance of coating and analyzing its microstructure, the following conclusions can be drawn:seen from the surface to the center, the sediments consist of white layer, ingredients of electrode, transition layer formed due to the processing of lubricant’s diffusion, heat-affected zone, and substrate. The surface which was made of numerous granules condensed after melt was smooth, tidy, and good-quality, and the phenomenon of’splashing’existing on the surface was obvious, too. As a result of residual stress, there were cracks on the surface.By using the FEA software ANSYS, the distribution of stress of self-lubricating coating in the processing of friction was analyzed, and the models to calculate contact stress of the pairs of ball-plate and spindle-ball were deduced too. Results show that: the distribution of compressive stress of the interface was uneven, while the stress in the middle of contacting surface was maximum, other areas’stress decreased gradually, which indicated that the coating weared most heavily in this experiment. Speed and load can only influence the intensity of stress with little impact on the distribution of stress regarding to this two types.The friction and wear properties of self-lubricating coating were studied roundly, meanwhile, the influence of speed, load and friction time on these properties in different forms of friction was discussed further. The results indicated that:as for these two distinct forms, friction coefficient increased as speed becomes higher, but decreased as load increases; changes of wear loss were proportional to these two influencing factors. The results of analyzing the surface appearance of self-lubricating showed that:there was a layer of lubricating film that can reduce the friction coefficient and wear rate of coating; as load increases, there would be more cracks which affected wear resistance of coating. The researches into lubricating mechanism of coating showed that the extra existence of BN which coutered wear loss of coating during the processing of friction can be favorable to the forming of lubricating film as well as improving friction and wear properties of self-lubricating coating of Cu-BN.