Highlights:Graphical/Tabular Abstract The designing and manufacturing of pindisc type tribometer Wear experiments under different environmental conditions The statistical calculation of the coating lifetime for a specific reliability value A pin-disc type tribometer was designed and manufactured for wear and friction tests. Figure A. The variation of average friction coefficients by different experiment weights Purpose: The aim of this study is to investigate tribological properties of MoS2 and graphite coatings under different environmental conditions. Theory and Methods:In this study, 10 mm in diameter and 20 mm length made of AISI1008 steel samples coated with graphite and MoS2 powders which widely used today as a solid lubricant with lead-spinning method. The experiments were carried out under three different environment; dry, oily and oil + 5% Molykote-A added. The properties of the abrasioned surfaces of the samples were investigated by optical microscope and scanning electron microscope. For 30%, 60% and 95% reliability values, the lifetime values of MoS2 and graphite coatings were statistically calculated. Results:In dry environment, MoS2 and graphite coatings were found to reduce friction by an average of 42% and 51%, respectively. The friction coefficients for MoS2 and graphite coatings in oily medium, were respectively about 10 times and 8 times lower than those in dry environment. In investigation of abrasioned surfaces, it was seen that scratch marks and locally metal regions on abrasioned surfaces which had worn in dry environment. In case of oily environmental, the coatings were superficially worn and no metal region was seen on abrasioned surfaces. The coating lifetime for MoS2 coated sample was calculated to be approximately 31.7 minutes and the lifetime for the graphite coated sample approximately 32 minutes. Conclusion:According to the results of the experiments, it has been found that coating any machine element surfaces with MoS2 or graphite can dramatically reduce the friction coefficient under dry environment. Limit of no use thickness (15 μm) that is also coating thicknesses of MoS2 ang graphite coated samples can withstand abrasion for approximately 32 minutes for 95% reliability with a test weight of 2 kg in dry environment.
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