Detecting Wear and Migration of Solid-Film Lubricants Using Simultaneous Exoelectron Emission

This study was carried out to see if solid-lubricant films on metal surfaces wear monotonically, or if there is occasional migration from a region on the wear track with copious lubricant to one from which the lubricant has been worn away. To facilitate this study, a new pin-on-disk apparatus was constructed with the capability of continuously measuring the friction and the exoelectron emission from tile wear track. Sliding tests were carried out using a circular wear track which, initially, traversed a path partly on an unlubricated surface and partly on a surface covered by a solid-lubricant film. It was found that lubricant films of rubbed graphite and molybdenum disulfide showed no spreading of the lubricant along the wear track, but polytetrafluoroethylene had some capability for migration and, hence, healing of a denuded wear track.