AES investigation of the transfer and chemical behaviour of MoS2 in rolling contacts

The chemical modifications occurring during rolling in steel contacts lubricated by magnetron sputtered MoS2 thin films were investigated using Auger Electron Spectroscopy (AES). Rolling conditions were established between an uncoated and three MoS2 coated AISI440C balls using a four ball tribometer operating at a contact pressure of 3.6 GPa. The degradation of the MoS2 coating and the nature of the transfer film were investigated using AES mapping, sputter depth profiling and line scans. Coating degradation was found to occur by wear and by materials transfer to the uncoated ball. Chemical reaction of transferred MoS2 with oxygen and the steel ball was observed. The reaction involves the formation of Molybdenum and Iron-Chromiun oxides and the elimination of Sulphur.