EFFECT OF ZDDP AND FULLERENES ADDED TO PAO 8 LUBRICANT ON TRIBOLOGICAL PROPERTIES OF THE SURFACE LAYER OF STEEL BARE STEEL AND W-DLC COATING

Abstract

The paper presents the effect of adding zinc dialkyldithiophosphate (ZDDP) and/or fullerenes on the properties of tribological systems coated with diamond-like carbon coatings doped with tungsten (W-DLC) and 100Cr6 steel without coating. The tribological tests were performed using a ball-on-disc tribometer. Discs made of bare 100Cr6 steel and discs with W-DLC coating were used as samples. Balls made of 100Cr6 steel were used as counter samples. The lubricants used:poly (α) olefin oil PAO 8, PAO 8 + 1.5% of ZDDP, PAO 8+ 0.005% of C60 fullerenes and PAO 8 + 1.5% of ZDDP + 0.005% of C60 fullerenes. Observations of the W-DLC coating were carried out using a scanning microscope, and the EDS analysis enabled the identification of the chemical composition along the cross-sections of the coating. A confocal microscope operating in the interferometric mode was used to analyse the geometrical structure of the samples before and after the friction tests. Observations of the wear marks on the samples and counter-samples were also carried out using a scanning microscope, and the chemical composition on the surfaces of the friction pairs was determined. The obtained test results indicated that the PAO 8 + ZDDP + C60 lubricant caused a reduction in the coefficient of friction and the linear wear in the tested steel friction pairs. In the case of W-DLC coating, however, the ZDDP added to PAO 8 increased the resistance to motion with a simultaneous improvement in anti-wear properties.