Study On The Mechanical Performances Of DLC-coated NBR Rubber Modified By Ti-C Interlayer

Rubber seals are widely used in lubrication systems and bearings to avoid leakage of lubricants and to prevent dirt and water entering the system.However,rubbers exhibit very high coefficients of friction(Co F)when sliding against most engineering materials,which can be easily damaged at high sliding velocity and tends to adhere to the counterpart.Under heavy working conditions,rubber seals are subjected to severe wear leading to an increase in clearance,which is often the cause of loss of function and failure of the lubrication system.Diamond-like carbon films are attractive as protective coatings due to the low friction and excellent wear-resistant to enhance the mechanical performance of rubber seals.Nevertheless,the mismatch in the physical properties of DLC films with elastomer materials easy to triggers the peel-off or delamination of films,thus impairing its industrial wide applications.In this paper,from the materials selection of interlayers and the design of structure to promote the adhesion strength between DLC films and rubber substrates.Also,to achieve an excellent wear-resistance of DLC coating coated on rubbers.The abrasiveness is the goal,which can provide reference process methods and technical data for the promotion and application of rubber products.Titanium-doped carbon(Ti-C)films prepared by dual-target magnetron sputtering,the influence of interlayer magnetron sputtering parameters on the mechanical properties of DLC-coated rubbers were studied.Besides,to obtain the good interface adhesion of DLC-coated films on rubber by optimize the deposition process parameters,which could achieve the well wear-resistance of superhard coatings on the rubber and the wide application on the rubber products.Moreover,the mechanical properties of Ti doped DLC deposited on NBR were further studied.The different gradients of Ti doped DLC films were obtained by regulating the sputtering power of Ti target.The friction and wear mechanism of Ti doped DLC films under dynamic working conditions was explored to promote the engineering application of DLC coated modified rubber seal materials.Firstly,a Ti-C thin film with a certain thickness was prepared under different substrates with negative bias as the interface transition layer.The influence of the interface layer process on the adhesion and wear resistance of DLC-coated NBR was studied.The surface morphology and structure of Ti-C thin films were studied by atomic force microscope(AFM)and Raman spectroscopy,and the composition of Ti-C transition layer was analyzed by XPS.The results show that with the increase of the substrate negative bias,the surface roughness of the DLC film with Ti-C transition layer gradually increased from 82 nm to 116 nm.The XPS results of the transition layer show that the Ti(5.2～8.3 at.%)Content also gradually increases with the increase of the substrate negative bias.The scratch strength and tribological properties of the DLC film coated on the NBR substrate were evaluated using a scratch meter and a ball-and-disk friction machine,respectively.It was found that the friction coefficient(Co F)of the DLC coating on the Ti-C transition layer prepared at a bias voltage of-150V was the lowest,only～0.18,and the scratch test results showed that the film crack width was also the smallest under this process.The results of mechanical characterization show that the introduction of Ti-C transition layer can increase the bonding strength of DLC and NBR and improve the wear resistance of NBR.Subsequently,the effect of substrate negative bias voltage applied to the Ti-C interlayer on the adhesion properties and tribological behavior of DLC films on NBR have been explored.The surface topography and structure of Ti-C films were investigated by atomic force microscopy(AFM)and Raman spectra.The composition of DLC films was analyzed by X-ray photoelectron.The adhesion strength and tribological properties of DLC films coated on NBR substrate were scrutinized by a scratch tester and a ball-on-disk tribometer,respectively.It was found that DLC film with a Ti-C interlayer at a bias of-150 V exhibited superior wear resistance with a low coefficient of friction(Co F)OF～0.18.Besides,the scratch test also revealed a reliable adhesion when the interlayer was prepared at-150 V,with a lowest scratch crack width of～50μm.Therefore,a Ti-C interlayer could significantly enhance the adhesion and wear resistance of DLC thin films deposited on NBR.Finally,the dual-target dual-power magnetron sputtering method was used to directly synthesize Ti-doped DLC films deposited on the NBR for single-factor research.The surface morphology,composition structure,and surface wettability and mechanical properties of Ti-doped DLC films on NBR.The results show that by adjusting the RF power of the Ti target,at 60W of RF-power,the Ti-doped DLC film exhibits excellent friction properties,the Co F is only～0.00142,and the film surface has no clearly wear scar.The doped DLC film prepared by this process exists as a sp~2 cluster-like graphite structure.At this time,the sp~2/sp~3 film is adjusted to a suitable ratio.However,the abrasion resistance improvement of Ti-doped DLC films is unstable.For films prepared at other powers,SEM can clearly observe the wear profile,and the film completely falls off to expose the NBR substrate.The contact angle test results show that the Ti-DLC film-coated NBR surface has a water contact angle(CA)value of 100.8°～111.05°.With the increase of RF power,the Ti-DLC film still maintains hydrophobic properties and the surface free energy is less than 22 m N/m,keeping low-energy surfaces.