Low friction composite coating of CrxSiy/MoS2 on steel

The manufacture of the system tool steel/intermediate layer of CrxSiy/low friction MoS2 film was achieved by r.f. magnetronsputtering. The substrate material was X100CrMoV51 with a surface roughness of Rz<100 nm and average roughness of Ra<10nm. The intermediate layers of Cr3Si, CrSi and CrSi2 varied in film thickness between 150 and 300 nm, and the MoS2 film was 300 or 600 nm thick. The films, deposited without a substrate heating, were amorphous, as shown by X-ray diffraction, and homogeneous in chemical composition (determined by secondary ion mass spectrometry and Auger electron spectroscopy). The CrxSiy films corresponded in chemical composition to that of the target material but the low friction MoS1.86 film (examined by ESMA) was understoichiometric. The oxygen content was below the detection limit of less than 5 at.%, as is shown in the Auger electronspectroscopy measurements. The tribological pin-on-disk experiments were carried out with ceramic, cemented carbide, stainless st eel and with coated steel as the pin material. These experiments showed a significant effect of the chemical composition of the intermediate layer on the tribological behaviour of the multilayer film. The pin-on-disk tests were carried out under the following standard conditions: load, 5 N; feed, 0.1 m s-1; temperature, 22xC; relative humidity 40%. The layer system Cr3Si/MoS2 showed the best values, with the disk undergoing 5000 rev and the pin covering a sliding distance of 9 m. These values decreased with increasing silicon content in the intermediate layer. Thinner films yielded the same relationships with smaller absolute values. The friction coefficients f are independent of the film thicknesses: 0.05 for MoS2, 0.07 for CrSi2/MoS2, 0.09 for CrSi/MoS2 and 0.1 for Cr3Si/MoS2.