| It is urgent to develop lubrication materials with superior tribological properties in room temperature to high temperature environments which needs to be solved in cutting-edge industries such as aerospace,chemical and metallurgical industries.Most common lubricants perform well only within a narrow temperature range,such as graphite,molybdenum disdlfide which are effective below 400℃in air,but oxideze,decompose and finally lose ther lubricious nature at high temperatures.Some nitrides and oxides lubricant work well at high temperature,but they become abrsive at lower temperature.The combination of two or more lubricants is one of the dominant methods to realize lubrication over a wide temperature range.The composition and structure of the friction interface elements are adjusted according to the operating temperature range,so as to deepen the understanding of the lubrication and failure mechanism and provide strong technical support for the high-end development of industrial equipment.In this thesis,self-lubricating materials with wide temperature range are desgined from the aspects of lubrication components,mechanical properties and multi-layer regulation,and self-lubricating composite multi-layer films containing Mo S2,Ag,Mo N and other elements were designed and deposited on the surface of superalloys by reactive magnetron sputtering.The medium and low temperature lubrication stage of Mo S2 or soft metal Ag,the high temperature lubrication stage of sulfide or oxide,and the high temperature migration lubrication of nickel-based alloying elements were used.The synergistic lubrication effect of multiple lubrication phases was also studied in a wide temperature range and the mechanical properties of films on the basis of ensuring lubrication were improved.The composite application of mechanical properties and tribological properties was explored which has important guiding significance for solving the safe operation of workpieces under special working conditions such as aerospace,metallurgy and chemical industry.The tribological properties of the composite films in a wide temperature range were studied by a high-temperature tribological tester.The phase changes before and after friction were analyzed by XRD and Raman spectroscopy,and the 3D Optical Profiler（UP-Lambda,American）was used to measure the surface roughness（Ra）of the films.The morphology and composition of high-temperature wear surfaces were analyzed by scanning electron microscope（SEM）and electron energy spectroscopy（EDS）.Mo N（Ag）composite films depoed with W or Ta elements was prepared by reactive magnetron sputtering.The results showed that the doping of W or Ta elements can make the structure of Mo N（Ag）-based composite films more dense,and improved the hardness and medium and high temperature tribological properties of the film.Especially at 600℃,W and Ta elements can effectively inhibit the migration of Ag elements in Mo N（Ag）composite films to the surface,forming friction lubricant films dominated by Mo Ox and various silver molybdate lubrication phases.And at 800℃,the Ni Mo O4 lubricating phase was formed by the diffusion of the substrate Ni elements and other lubrication phase co-lubrication jointly reduced the coefficient of friction（COF）between the friction pairs,based on which the Mo N（Ag）-based composite films can be applied in a wide temperature range.On this basis,Mo N（Ag-Ta）composite film with excellent medium and high temperature tribological properties was selected as the research object,and Mo S2 lubricated phase was introduced to design the multilayer structure.Through the analysis of the mechanical properties and tribologiacal properties of Mo N（Ag-Ta）-Mo S2（Ag）multilayer films,it is found that multilayer films doped with Ta elements can effectively inhibit the migration of Ag elements in Mo N（Ag-Ta）films.Among them,the 2-Ta multilayer film improved the hardness and medium and low temperature tribological properties,so that the multilayer Mo N（Ag-Ta）-Mo S2（Ag）can be applied in a wide temperature range.Similary,on the basis of the above mentioned content,Mo S2 and W elements were introduced to prepare Mo N（Ag-W）-Mo S2（W）multilayer films by reactive magnetron sputtering.On the one hand,the W elements was introduced in order to improve the mechanical properties of the multi-layer film and reduce COF between the friction pairs in the high temperature environment;on the other hand,the purpose of introducing Mo S2 is to improve the tribological properties of multi-layer films in medium and low temperature environments.It is found that the Mo N（Ag-W）-Mo S2（W）multilayer film dopef with W elements can not only effectively improve the surface roughness of the film,but also effevtively inhibit the migration of Ag element in the Mo N（Ag-W）film.Among them,the 8-W multilayer film shows a good antifriction and lubrication effect in a wide temperature range,and its COF was always maintained below 0.25 from room temperature to high temperature environment,so that multilayer film can be applied in a wide temperature range. |
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