In-situ instrumentation to observe transient tribological effects in high sliding speed unlubricated contacts

Abstract

Non-invasive and high data rate instrumentation methods are critically needed for in-situ monitoring and analysis of transient effects of high sliding speed dry mechanical contacts of gears and bearings, where increases in temperature and changes in surface chemistry control the tribological response. This study examines some of the approaches on an example of an unlubricated contact of a silicon nitride ball on a steel disk operating in humid air at about 1.5 GPa contact pressure with variable high sliding speeds (ranging from 1 to 16 m/s), while using correlated in-situ optical imaging and thermography to aid in the analysis of changes in tribological response. In-situ optical imaging of wear tracks with quantified color analysis was used to detect the increased tribochemical activity, and thermography helped to correlate this tribochemical activity with thermal effects induced by the frictional heating. The post-experiment analysis with scanning electron microscopy and energy dispersive spectroscopy elemental mapping confirmed the development of the oxide based tribofilm correlating to the changes in the optical imaging and thermography. The results indicate that both employed in-situ methods were effective in the measurement of signals that were related to changes in the mechanical or tribochemical behavior of high speed sliding contacts, linked to transitions in the coefficient of friction from a high value to low, and accompanied by the transition from oxidative wear to the formation of a complex tribofilm at speeds above 4.5 m/s. The discussed instrumentation methods and data analysis approaches enhance the in-situ capability for evaluating transient tribological effects at high sliding speeds and contact loads.