Application of the contact potential difference technique for on-line rubbing surface monitoring (review)

Abstract

The Kelvin technique for measuring contact potential differences has been adapted for continuous non-destructive monitoring of changes in the electron work function of a rubbing surface. The method can be used to investigate tribological materials for a wide range of conditions, including changes in load, sliding speed, and environment, with or without lubrication. It relies on the sensitivity of the work function to the various events which accompany friction, e.g., plastic deformation, creation of new surface material, adsorption, oxidation, phase changes and redistribution of alloy components. At present, this is the only method which is sensitive to both surface and near-surface defects and permits study of one of the two interacting surfaces during sliding. Current work emphasizes two aspects of sliding behavior: (1) critical points with respect to changes in normal load, with relevance to materials selection and optimization, and (2) the kinetics of friction processes, including periodic changes which may be related to those in fatigue.