Effect of Sliding on the Relation of Tribofilm Thickness and Wear

The formation of tribofilms depends on temperature, shear stress, availability of the related chemical components, and characteristics of the near surface region, e.g., roughness and surface chemistry. The purpose of a tribofilm is to separate two sliding surfaces, thus preventing or limiting wear. This research article aims for the first time at a systematic approach to elucidate on a fundamental level the interplay between tribofilm formation in particular thickness and wear behavior in the boundary and mixed lubrication regime. For this, load, temperature and sliding frequency as most relevant parameters are taken into consideration. For that purpose, a piston ring and cylinder liner configuration in an oscillating tribometer was chosen as a model system, with the top dead centre conditions in internal combustion engines of passenger cars as the testing regime. The amount of wear produced during the tribotests is continuously monitored by means of the Radio-Isotope Concentration (RIC) method. The tribofilm is investigated via Atomic Force Microscopy (AFM), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) and X-ray Photoelectron Spectroscopy (XPS). The results clearly indicate that the impact of load on the wear rate can be seen in an Archard-like dependency, but changes of temperature and sliding velocity in the boundary to mixed lubrication regime imply a non-linear ratio between wear and tribofilm formation