The Effects Of SiN_x On The Microstructure,Mechanical And Tribological Property Of Wide-range Temperature Self-lubircant Mo₂N-Ag Nano-structured Films

The friction and wear have an important influence in the progress of human society.the lubrication,as the main way to improve friction and wear resistance,is one of the primary way to ensure the efficiency and reliability of mechanical transmission.Traditional lubricants,such as oils or greases,have excellent lubrication property in quite a narrow temperature range and are environment unfriendly.Thus,it is of great significance to use surface engineering theory to develop environmental-friendly film material that have a wide temperature range antifriction and wear resistant to meet the needs of today’s mechanical engineering technology.This thesis achieved control release and isolation from oxygen environment of room and medium temperature lubricating phase Ag and high temperature lubricating phase Mo₂N by adding amorphous hard phase SiN_x,based on the idea of capsule controlled-release and the theory of multi-component synergistic lubrication,and design and deposit Mo₂N-Ag-SiN_xcomposite films,Mo₂N-Ag/SiN_x and Mo₂N-SiN_x/Ag-SiN_x multilayer films,obtain lubrication behavior law under temperature cycling condition based on the friction reaction products by researching the interaction between amorphous protective phases and various lubricating phases,providing experimental support for the design and preparation of green Mo₂N-based composite films and multilayer films with long-term lubrication performance in a wide temperature range.The research content is as follows:（1）Mo₂N-Ag-SiN_x composite films with various Si contents were deposited using a magnetron sputtering system.The microstructure,mechanical properties and lubricating properties at room temperature and 600℃high temperature were characterized.The results showed that The Mo₂N-Ag-SiN_x composite film consists of fcc-Mo₂N phase,fcc-Ag phase and amorphous SiN_x phase.With the Si content increase,the hardness of composite film first increases slightly then maintained（its value is similar to SiN_x）.Si content have significant influence on the tribological properties of the film at room and 600℃high temperature condition.At room temperature,the friction coefficient of the composite film decreased slightly with the increase of Si content（Si content less than 1.3 at.%）,and then remained stable.The wear rate of the film decreases first and then increases with the increase of Si content,which is mainly affected by the hardness of the film.This is mainly affected by the hardness of the film,the increase of hardness leads to higher wear resistance of the film.Under the condition of high temperature friction at 600℃,with the increase of Si content,the friction coefficient and wear rate of the film decrease first and then increase.The main reason is that proper addition of Si content can effectively control the migration of lubrication phase at high temperature,so that the lubrication time of the film is longer.At this time,the film has good lubrication and mechanical properties,so the friction coefficient and wear rate decrease.the self-lubricating performance of the film be reduced with excess Si contents,resulting in the decline of the film lubrication performance,and high levels of Si content will lead to a large number of hard debris in the friction process,resulting in an increase in the wear rate.（2）Mo₂N-Ag/SiN_x multilayer films with a fixed modulation ratio（thickness of Mo₂N-Ag to SiN_x）of 3:1,with changing modulation period（Λ,thickness of Mo₂N-Ag and SiN_x）from 8 to 200 nm were produced using a magnetron sputtering system.Results showed that a dual-phase of fcc-Mo₂N and fcc-Ag co-existed in Mo₂N-Ag layers,while the SiN_x layer exhibited an amorphous character.Both room temperature（RT）lubricant and wear-resistance properties of the films were improved by increasingΛfrom 8 to 64 nm,which was attributed to the increase in the thickness of the lubricating layer Mo₂N-Ag in the film,and the film had relatively high hardness at this stage,so the wear rate of the film also decreased.while a further increase ofΛdegraded the wear-resistance properties,This is because the high thickness of Mo₂N-Ag leads to the decrease of the film hardness,and the increase of the thickness of SiN_x layer leads to the increase of hard debris,which leads to the decrease of the wear resistance of the film.The multilayer film atΛ=64 nm exhibited an excellent RT-500°C temperature-cycling tribological properties.Mechanical properties and the synergistic effect of both modulation layers attributed to the improvement on the tribological properties.（3）Mo₂N-SiN_x/Ag-SiN_x multilayer films a fixed Mo₂N-SiN_x modulation layer thickness of 10 nm with changing Ag-SiN_x modulation layer thicknesses from 2 to 12 nm were deposited using a magnetron sputtering system.Results showed that fcc-Mo₂N phase and amorphous SiN_x phase co-existed in Mo₂N-SiN_x layer,while the Ag-SiN_x layer is composed of amorphous SiN_x and fcc-Ag phase.The interface between the two modulation layers of the multilayer film is clear,and the friction and wear properties of multilayer films are greatly impacted by the thickness of the Ag-SiN_x modulation layer at room temperature friction and wear test.The friction coefficient slightly decreases with the increase of the thickness of the Ag-SiN_x modulation layer,and the wear rate first decreases and then increases with the increase of the thickness of the Ag-SiN_x modulation layer,which is mainly influenced by the hardness of the multilayer film.The increase of hardness is beneficial to the wear resistance of the film,at this time,the wear rate decreases,while the decrease of hardness leads to the film is easier to be worn,at this time,the wear rate increases.The friction coefficient decreases slightly with the increase of Ag-SiN_x modulation layer thickness,which is because the content of Ag phase in chamber and medium temperature increases with the increase of Ag-SiN_xmodulation layer thickness,which provides good lubricity at room temperature for the film.The multilayer film has excellent anti-friction performance at 600℃,and the friction and wear performance of multilayer films are almost not affected by the thickness of Ag-SiN_xmodulation layer,this is mainly because the friction physical and chemical reactions occur under the double action of high temperature and sliding friction pair.The low friction coefficient of the film at high temperature also alleviates the interaction between the friction pair and the wear mark,so that the beneficial wear resistance is not affected by the change of the thickness of the modulation layer.