| Electrical contact materials are prone to wear-out failure due to long-term service in sliding contact environments.Therefore,it is necessary to research and develop composite materials with excellent electrical conductivity and remarkable anti-friction effect.If the composite films deposited by unbalanced magnetron sputtering technology can meet the performance requirements of electrical contact materials,it can provide a new technical approach for the preparation of electrical contact materials.In this thesis,Cu-Ag thin films doped with different Ag contents were prepared on the bronze substrate by adjusting the Ag-target sputtering current and sputtering bias.The effect of changes in roughness,thickness,Ag-content and micro-structure caused by process parameters on film surface resistance was studied.The change law of bonding strength,hardness,friction coefficient and wear rate with the current of Ag-target was analyzed and the wear mechanism was revealed.Based on the process with better comprehensive good performance of Cu-Ag thin film,Cu-Ag-C composite thin film was co-deposited by adjusting the C target current,and the changes of its electrical conductivity,mechanical properties and tribological properties were studied.The result shows:For Cu-Ag thin films prepared under different Ag-target currents,when the current is small,a small amount of Ag solid solution in Cu caused the sheet resistance to increase.The super-saturated elemental silver after Ag target current 0.5A lead to a reduction in sheet resistance.When the Ag current was 1A,the thin film columnar crystal penetrates the thickness of the thin film,and the sheet resistance further decreased.The decrease of the thickness of the Cu-Ag film and the slight decrease of the silver content caused by the increase of the sputtering bias did not cause the increase of the sheet resistance.Instead,the reduction of the surface roughness and the improvement of film density under high bias reduced the sheet resistance.The main reason for the change of the sheet resistance of Cu-Ag-C film under different C target currents was the microstructure.The addition of carbon hindered the dominant orientation growth of Cu(111)and Ag(111)crystal planes,and the crystalline state tended to grow amorphously,leading to an increase in the sheet resistance.As the C-target current continues to increase,graphitization causes a reduction in the sheet resistance.The sheet resistance of Cu-Ag-C film was still slightly higher than that of the Cu-Ag film,but the sheet resistance did not increase much when the C-target current was 1.1A.The characterization of the scratch method revealed that the bonding strength of the Cu-Ag film and the Cu-Ag-C film was good.The solid solution of a small amount of Ag increased the hardness of the Cu-Ag film,and the hardness gradually decreased with the increase of Ag-content.The Cu-Ag-C film tends to grow amorphously,resulting in a significantly higher hardness than the Cu-Ag film.The hardness of Cu-Ag-C film is significantly higher than that of Cu-Ag film.The thin film structure tended to be graphitized resulting in a slight decrease in hardness when the C-C bond content of the sp~2 hybrid increased.The friction coefficient of Cu-Ag film is slightly higher than that of the substrate,but the wear rate is almost all lower than that of the substrate.Among them,the wear rate was the smallest at 0.3A of Ag current,which decreased by 28.8%when compared with substrate and dropped by 18.9%when compared with pure copper film.It indicated that the addition of appropriate amount of silver can improve the wear resistance of the film.The wear mechanism of Cu-Ag alloy film and steel ball mainly showed adhesive wear,accompanied by abrasive wear,fatigue wear and oxidative wear.The friction coefficient and wear rate of Cu-Ag-C films were lower than Cu-Ag film.When the C-target current was 0.1A,the friction coefficient of Cu-Ag-C film decreased the most,about 16%.When the C target current was 0.7A,the film wear rate decreased by 14.1%and the sheet resistance did not increase much.The addition of C component obviously strengthened the film,and the bearing capacity of the film-based system was improved.Simultaneously,the peeling of the film layer caused by adhesive wear was reduced.Cu-Ag-C film could further improve the friction reduction effect without increasing or decreasing the film sheet resistance. |
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