Tribological behavior of molybdenum coordination compound without sulfur and phosphorus as oil additive for steel-steel contact

A new kind of molybdenum coordination compound (MCC) without sulfur and phosphorus was prepared and evaluated as a promising lubricant additive for steel-steel contact. Tribological behavior of synthetic MCC as a lubrication additive for a steel-steel contact was comparatively investigated on SRV test rig with (ball-on-disc configuration), using paraffin as a comparison. The worn steel surfaces lubricated with paraffin and 1% MCC + paraffin under different loads were observed by scanning electron microscope, and the chemical states of some typical elements on the worn surfaces were analyzed by X-ray photoelectron spectroscopy. It was found that the synthesized MCC in the paraffin base oil significantly reduced friction coefficient and wear rate. Paraffin containing 1wt% MCC additive showed better friction-reducing and anti-wear abilities compared with paraffin without additives. Meanwhile hardness on worn surface, when lubricated with 1% MCC + paraffin, increased during friction and wear process, which contributed to reducing friction and wear of both tribo-pairs. Significant improvement of friction and wear, is due to action of the boundary layer and MCC deposited on the worn steel surface which prevent direct steel-steel contact from severe adhesion, scuffing, and seizure.