On the mechanisms of MoS₂-film failure in sliding friction

The effect of oxygen on the life expectancy of a run-in molybdenum disulfide film under heavy load has been studied. Tested in argon, with only small quantities of oxygen present, the smooth running period is increased by at least two decades as compared to a test in oxygen. Blister formation is an important phase in the gradual destruction of the lubricant film. Blisters of submicroscopic size can be traced with the electron microscope, and in the presence of oxygen macroscopic blisters are rapidly formed; their further history has been followed by cine-film. Oxygen promotes sintering of the individual particles 10 a continuous, smooth, and therefore highly reflective lubricant layer. This process is an essential condition for blistering. No wear occurs during the smooth running period of MoS2 lubrication. Graphite differs from MoS2 in this respect and in its much lower load-carrying capacity. The cine-film of graphite-lubricated surfaces indicated a rougher surface and the formation of smaller blisters. On addition of graphite to MoS2, a sudden change in surface features occurs within narrow limits of graphite concentration. It seems that the addition of 15% by weight of graphite increases the total life expectancy of the MoS2 film, but reduces the length Of the smooth running period.