| As a sealing material,rubber has been widely used in bearing and piston seals,but its high friction coefficient and wear rate shorten its service life.Magnetron sputtering is an alternative method for depositing super-hard films on rubber surfaces.The desired rubber surface properties can be obtained by this method with almost no change in rubber's volume size.Diamond-like carbon(DLC)is a kind of super-hard material,which is usually applied to the surface of the material to improve its mechanical properties.DC magnetron sputtering technology is a very good method to prepare DLC film on rubber surface due to its simple process and fast deposition rate.However,its preparation process will greatly affect the properties of deposited DLC film,thus affecting the effect of rubber modification to enhance wear resistance.Therefore,it is important and necessary to study the sputtering process in order to extend the application field of the rubber seals with long life.In this paper,NBR,which is commonly used in rubber seals,was taken as the research object to prepare DLC film on NBR by DC magnetron sputtering.The influence of three process parameters on the tribological properties of DLC film prepared on NBR and the change of sealing properties after modification were studied.The influence of argon sputtering pressure on surface morphology,structure,wettability and tribological properties of DLC films was studied.The morphology of DLC film on rubber surface and its relation with pressure were observed and analyzed by atomic force microscope.The chemical bond structure of DLC film was studied by Raman spectrum and the structure was verified by infrared spectrum.Tribological tests were carried out under the condition of dry room temperature and fixed load of 0.3 N by the ball-on-disk friction method.The results showed that low friction coefficient could be obtained by adjusting the pressure of film deposition.Then the influence of negative bias on DLC film prepared on NBR was studied.The composition of DLC thin film was analyzed by X-ray photoelectron spectroscopy,and the chemical bond of DLC thin film was confirmed by the combination of Raman analysis.The mechanical properties of DLC films deposited on NBR surface under different negative bias of substrate were tested by Nanoindentation apparatus.The results showed that the hardness and Young's modulus of NBR increased with the increase of bias voltage.Tribological tests showed that DLC films deposited at bias voltage of-200 V could obviously improve the hardness of NBR and reduce the wear rate.After that,the influence of power on DLC thin films prepared on NBR was studied.The densification of the thin film was observed and evaluated by scanning electron microscopy.It was found that the thickness of DLC film prepared under high power increased,and high film thickness could effectively improve the friction and wear performance of NBR.Finally,the definition of surface roughness was briefly introduced,and the critical connectivity theory was used to evaluate the possible conditions of leakage after contact between rubber and hard surface.By virtue of the volatility of ethanol liquid,a simple experimental device designed by the author compared and evaluated the leakage rate of rubber and DLC-coated rubber.By analyzing the leakage rate under two different stress and time conditions and comparing with the results of theoretical calculation,the leakage rate evaluation theory system with Young's modulus and root-mean-square roughness as correlation factors was established. |
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