| The diamond has many excellent characteristics.Such as high hardness,large elastic modulus,high thermal conductivity,low friction coefficient and some stable chemical properties.Therefore,it can be used as a friction-reducing and wear-resistant,protective material.It can be prepared on some devices like bearings and tools in order to improve the wear resistance.The little change can improve the efficiency and life of these devices obviously.In addition,water is a renewable resource and can be used as a clean lubricant,and the corrosion resistance of diamond can restrict the corrosive effect of water.This thesis used high filament chemical vapor deposition(HFCVD)to prepare film and used cemented carbide as the substrate material.The structure of the diamond coating was studied.The molecular dynamics model of the friction between diamond and Si3N4 was established theoretically.At the same time,the friction behavior between molecules was studied.This thesis has studied some factors which can influence the friction and wear behaviour of diamond coating during the experiment.These factors include the methane concentration,load,lubrication conditions and so on.The specific content and details are as follows:(1)The paper introduce the method of molecular dynamics simulation firstly.The contact model of diamond and silicon nitride material was established subquently.The most important thing were used molecular dynamics to simulate the friction behavior of the two materials,while observe the atomic motion state and friction by changing the number of the pressed depth.Not just that,the transformation law of force and friction coefficient which can be seen from the mode shows that the relation between force and friction coefficient is inversely proportional.Nevertheless,the coefficient of friction is increasing with the pressure.(2)Different diamond coatings were prepared by using different methane concentration(1%～5%).The silicon nitride ball was selected as the matching pair while the diamond coating was used as the friction and wear test.During the process of friction,the load and methane concentration were analyzed comprehensively.The wear morphology was estimated using the light microscope.The data showed that the concentration of methane was increasing,while the surface roughness of the diamond coating was decreasing.It can be concluded that the friction process can be divided into three stages: the initial stage,the running-in stage and the stable stage.In the initial stage,the trend of friction coefficient basically decreased,while the methane concentration was decreasing;In the stable stage,the MCD film will have a local mutation,while SMCD film was relatively stable.When the load increased from 5N to 10 N,the initial stage and the running-in stage generally showed the tendency of reducing,and the fluctuation in the stable stage increased.With regard to the NCD film,the friction coefficient fluctuates greatly under a load of 15 N with no stable stage.The coating peeled off seriously.(3)The sub-micron film with better friction and wear performance is selected for the friction and wear test under dry friction and water lubrication conditions.On the whole,the friction behavior of water lubrication conditions during the friction process was better than that of dry friction conditions.When the load changed under water lubrication conditions,the friction coefficient changed following the different load at each stage.The initial stage became larger,but the stable stage became smaller.According to different conditions,water lubrication reduced the wear rate of diamond coating more obviously.The non-diamond structure under dry friction conditions was formed according to wear morphology and Raman spectrum.The wear morphology obtained under water lubrication conditions was doped with some oxide components.With the increase of load,the formation oxide film became faster.All these factors improved the friction behaviour. |
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