Surface Chemical Aspects in Boundary Lubrication

Boundary lubricating behaviors were investigated from the viewpoint of surface chemistry based on our results. Boundary lubricating properties are closely related to the chemical structure of boundary lubricating films. TOF-SIMS (time of flight secondary mass spectroscopy) which has several advantages such as high sensitivity, high spatial resolution and high chemical resolution was applied to chemical analysis of boundary lubricating films. Degradation of lubricating films on hard disk media was investigated by TOF-SIMS and removal of the lubricant oil and chemical wear of slider materials was observed. It was found that the tribochemical degradation of the oil was catalyzed by the slider material such as Al2O3 and TiN. The degradation was suppressed when DLC and c-BN were used as a slider material. Thin layer of PTFE on tribo-material composed of PTFE-PEEK was characterized by TOF-SIMS after lubrication tests with a steel ring. It was found that the surface coverage of PTFE was decreased with increasing contact pressure from 6 to 27 MPa and welding occurred when the surface coverage was less than 20%. A tracer method with stable isotopes such as H-2(D), C-13 and O-18 was introduced for characterization of boundary layer formed from organic additives. Effectiveness of chemisorbed ethyl alcohol-d5 (CD3CD2OH) for lubrication of CrN with alcohol was confirmed by TOF-SIMS analysis. An important role of nascent surfaces on tribochemical reactions to form boundary layers was investigated. For the reaction of EP additives, an organic sulfide was more reactive on nascent steel surface than organic phosphates. It was found that decomposition of synthetic hydrocarbon oil was catalyzed by nascent surface of steel under the effect of frictional heat.