Study On The Tribological Characteristics Of CrN Coatings Lubricated By Glycerol

In recent years,with the continuous development of industrial technology and increasingly harsh working conditions,people have put forward higher requirements for coating materials.Although CrN coating has received in-depth research,development and application due to its outstanding properties,it has a series of problems which greatly limits its further development such as low hardness and poor high temperature resistance.On the other hand,most traditional petroleum-based lubricants are toxic and nonrenewable,and there are still problems such as leakage and environmental pollution during use.Therefore,it is imperative to find a lubricant that not only meets people's normal production and life needs,but also has less environmental pollution.In order to solve these problems,on the one hand,the overall performance of the CrN coating can be improved by optimizing process parameters or through element doping.On the other hand,the tribological performance of the coating can be improved by selecting a reasonable environmentally friendly lubricant.Based on this,in this thesis,a series of CrN-based coatings such as CrN,CrAlN,and CrCuN were prepared by using DC magnetron sputtering technology.The environmentally friendly lubricants such as soybean oil and glycerol was selected as the lubricating medium to lubricate the coatings.We systematically studied their microstructure,mechanical properties and tribological properties in different lubricating media,and revealed their lubrication mechanism through XPS analysis.The main content of the paper is as follows:(1)The deposition temperature can directly affect the crystal orientation structure characteristics and mechanical properties of the CrN coating.The CrN-250 coating prepared at 250? has the densest structure,the best mechanical properties,and the best anti-wear performance under dry friction conditions.Under lubrication of soybean oil,the CrN-250 coating also exhibits excellent tribological properties,and its wear rate is only 5% of that of the uncoated substrate.XPS analysis shows that soybean oil will form a chemical adsorption film on the surface of the CrN coating after friction.The adsorption film can effectively reduce the friction and wear on the surface of the CrN coating.(2)Using glycerol as a lubricant for CrN coating can greatly improve the anti-friction and antiwear performance of the coating.Under the condition of glycerol lubrication,the friction coefficient of CrN-250 coating is as low as 0.02,showing extremely excellent lubricating properties.Studies have shown that during the friction process,glycerol molecules will be degraded by tribochemical reactions with iron oxide,and a layer of Fe OOH will be formed on the surface of the counter steel ball and CrN coating,which plays a key role in improving the tribological properties of the coating.The hydrophilic Fe OOH layer will further adsorb other products of glycerol degradation on the surface and form a fluid layer that separates the coating from the counter ball,thereby providing the steel/CrN system with lower friction and wear.(3)The microstructure,mechanical properties and tribological properties of CrAlN and CrCuN coatings are quite different.In the CrAlN coating,the Alelement mainly exists in the form of AlN phase,while in the CuCuN coating,the Cuelement exists as the metallic Cuphase.The hardness and elastic modulus of the CrAlN coating are significantly higher than those of the CrCuN coating,making it exhibit better wear resistance under dry friction conditions.However,when glycerol is used for lubrication,the tribological performance of CrCuN coating is much better than that of CrAlN coating,and its wear rate is two orders of magnitude lower than that of CrAlN coating.Through XPS analysis,it is found that glycerol is prone to tribochemical reaction and degradation on the surface of CrCuN coating during the friction process to form a friction film,thereby effectively reducing the friction and wear.