| For excellent electrical and tribological behaviors,metals such as Ag and Cu are widely used as electrical contact materials.The friction and wear of electrical contact parts are more complex than pure mechanical wear.The reliability and life of the entire electrical system are reduced by the wear failure of electrical contact parts surfaces,and accompanied by serious consequences and huge losses.Therefore,by means of the design and application of Ag,Cu and other coating materials with excellent current-carrying friction properties,the friction and wear problems of the electrical contact parts are effective solved.Magnetron sputtering is a green,efficient,and reliable method for preparing thin film materials,which is widely used for preparing various functional film materials.In this paper,pure metal film materials such as Ag and Cu were prepared by magnetron sputtering,and their electrical and tribological properties were tested by current-carrying friction experiments under conductive grease lubrication.The crystal structure and microstructure evolution of the metal films before and after current-carrying friction experiment were studied,and the current-carrying friction mechanism of magnetron sputtering Ag and Cu films was explained.The specific research contents are as follows:(1)Pure Al film prepared by magnetron sputtering was studied.It was found that the Al film get a typical crystal structure with a grain size of micrometers.Typical wear scar of Al films obtained from current-carrying friction experiments was selected for research.It was shown that the tribological performance of the Al film was not ideal as the Al film was worn through and the Cu substrate was exposed.By the comparative study of the original magnetron sputtered Al film and the residual Al friction film,it was found that the grain orientation changed significantly from(100)or(110)plane group orientation to(111)plane group preferred orientation,and the average grain size tended to decrease.(2)The Ag film prepared by magnetron sputtering got typical columnar grain structure composed by nanoparticles.Most of the grains grew along the(111)preferred orientation.Furrows,micropores,plastic flow,and spalling were found in the surface of the Ag film wear scar,and conductive grease components were found in the plastic micropores.The electrical performance of the Ag film was improved by the conductive grease filling in the micropores of the wear scar.(3)In this paper,FIB nano-sampling technology was used for the first time to prepare microstructure samples of Ag film.The crystallographic behavior of the wear scar near surface was studied using SEM-EBSD,TEM,and other characterization methods.Friction induced grain refinement was observed in the microstructure of the Ag film wear scar.High density nano twins Ag structures were observed,and {111}crystal plane group stacking faults were found.at the twin boundaries.It was shown that friction induced grain refinement improved the strength and the wear resistance of the Ag film.The high-density twin silver inclusion non-twin crystal microstructure is conducive to internal sliding of the Ag film material,thus improving its wear resistance.(4)The magnetron sputtering Cu film with fine nanocrystalline structure was tightly bonded to the copper substrate.Furrows were commonly found in the wear surface of the Cu film along the sliding direction.Carbon enriched in the furrows,indicating that the wear morphologies were conducive to the electrical conductivity of conductive lubricating grease,thus improved the electrical properties of Cu film.The grain refinement caused by friction was found in the FIB in-situ cut specimen of Cu film wear scar.In addition,GP region and twin region were found in the wear scar microstructure of Cu film,and a trend of friction induced GP region evolution to stacking fault structure was also found.It was concluded that the fine grain strengthening effect and the strengthening mechanism of nanostructures such as GP region and twin region improve the tribological performance of Cu films,and the nanoscale microstructure of GP region and twin region hardly affect the electrical performance of Cu films.(5)Crystal structures of magnetron sputtering Ag,Cu,and Al films were compared and studied.The results showed that Ag and Cu films got typical nanocrystalline structures,and the Cu film was finer.Based on the wear morphologies and current-carrying friction results,Ag film was the best,and the performance of Cu film was very similar to that of Ag film.Cu film cost lower,so that Cu film can be a great substitute for Ag film as electrical contact coating material in application.By comparing the crystallographic characteristics such as grain size,grain morphology deformation mode,and dislocation density between the wear scar deformation regions and the original metal film,with the Hall-Petch relationship and the Bailey-Hirsch relationship,it was derived that the different deformation regions of the wear scars of the metal film have different rheological shear stresses.When the rheological shear stresses value is greater than the yield stress value of the original film,wear increases significantly. |
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