Molybdenum Disulfide in Oils and Greases Under Boundary Conditions

Abstract

A mineral oil and a lithium-based mineral oil grease containing molybdenum disulfide are tested under boundary conditions on the Shell Four Ball Testing Machine and on a modified Reichert Wear Balance. The investigation of the wear tracks by scanning electron microscopy and microprobe analysis shows that a continuous MoS1 film is formed on the metal surface under mild friction conditions. Under extremely severe conditions, however, the MoS2 reacts chemically. It is found that molybdenum diffuses into the steel surface forming intermetallic compounds and carbides which improve the quality of the steel surface. The effect of time and pressure on the thickness of the molybdenum disulfide is determined and the amount of wear reduction by chemical reaction of molybdenum disulfide with the steel surface is compared to that of a traditional EP-additive.