| Diamond-like carbon film is a space amorphous carbon film composed of SP~2 and SP~3bonds of C.It has excellent mechanical,electrical,optical and acoustic properties,especially its high hardness and low friction coefficient,so it is widely used in the field of protective coating on material surface.One of the main tasks of this paper is to design the structure of DLC composite films and optimize the deposition process to obtain DLC composite films with excellent mechanical properties.High performance DLC/Cu-DLC/W-DLC composite coatings were prepared on stainless steel substrates by ECR-CVD and magnetron sputtering.When the mechanical properties of DLC composite film meet certain requirements,we attempt to apply it to the protective coating of aerodynamic bearing material to solve the wear problem caused by dry friction between rotor and bearing support surface,which can not form effective aerodynamic film during the start-stop stage of aerodynamic bearing.Considering the protection of bearing bush and DLC composite coating,the composite tribological behavior of graphite fluoride modified polyimide coating was studied from the point of view of the overall design of Tribological system.Firstly,#1W-DLC film,#2Cu-DLC/W-DLC film,#3DLC/Cu-DLC/W-DLC composite film and#4DLC/W-DLC composite film were prepared with the sputtering current of W target0.45 A and the current of Cu target 0.5 A.The surface morphology was characterized by SEM and AFM.It was found that the surface roughness of the#2,#3,#4 samples were much smaller than that of#1W-DLC film,and the DLC/Cu-DLC/W-DLC composite film had a minimum surface roughness of Ra=1.13 nm.The adhesion between the coating and the substrate for#3samples was 46 mN characterized by nanoscratch tester.Then,based on the above DLC/Cu-DLC/W-DLC structure,we optimized the deposition parameters of the composite films.The effect of W content on the mechanical and Tribological Properties were investigated by changing the sputtering current of the W targets.It was found that the hardness and elastic modulus of the composite films increased when the current varied from 0.3 A to 0.45 A,and decreased when the current changed from 0.45 A to 0.9 A.The composite film showed the maximum hardness of 35 GPa and the maximum modulus of elasticity of 352 GPa when the sputtering current of the W target was 0.45 A.Friction test with GCr15 steel balls showed that the friction coefficients of all samples were very low,between0.1 and 0.15.For the surface analysis of the wear track,the main friction mechanism was confirmed to be severe abrasive wear,and the tear zone of DLC film appeared in the#5 sample.Film transfer to the friction pair from the composite film was found during the friction process.The lower the hardness of the composite film,the more the transfer film was formed.At the friction test between the fluoride-modified polyimide coating with DLC/Cu-DLC/W-DLC composite films,the friction coefficients were between 0.05 and 0.09 under the pressure of 2-11 N.It showed that the friction mechanism was slight abrasive wear,and the wear rate of the DLC film is almost zero.The results of EDS and Raman of the wear scar of the composite films indicated that the graphite fluoride modified polyimide formed a transfer layer on the composite film.The polyimide transfer was dominant under the pressure of 2 N,and the amount of transferred fluorinated graphite increased gradually when the pressure was 5-11 N. |
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