The synergistic effect of copper powder with PTFE in a grease lubricant under mixed friction conditions

This paper describes experimental work on the frictional performance of a lithium grease lubricant filled with a combination of polytetrafuoroethylene (PTFE) and copper powders. The tribological testing was carried out in agreement with the prescriptions of the Polish standard PN-76/C-04147 using a four-ball apparatus. The performance of the tested compositions was evaluated using three criteria: ball wear d, limiting wear load G, and seizure loadFz. Synergy between action of the powders of PTFE and copper in compositions with 6 wt.% of these fillers was found. Examinations of the chemical composition of the upper layer of the wear scars of the tested balls were carried out using an X-ray microanalysis method with dispersion of the radiation energy. The results of these analyses made it possible to confirm the author's notion that the synergy of PTFE with copper in the lithium grease tested was possible due to the thermal decomposition of PTFE and the consequent creation of new layers during a reaction of the decomposition products with the platering layer of copper. These new layers are, to a high degree of probability, complexes with copper, sulphur, and fluorine.