Study of Wear Mechanisms and Characteristics of Coating Films on the FALEX® Block-on-Ring Tester Using SEM and EDAX

The friction and wear processes as well as some characteristics of the coatings formed under boundary lubrication regime were studied. For measuring the friction force as function of temperature and load, the block-on-ring Falex® tester was used. Stribeck curves were plotted from which the boundary lubrication regime was experimentally determined. Two full additivated lubricant oils with different mixtures of primary and secondary zinc dialkyldithiophosphate (ZDDP) additives were tested. To study the predominant wear mechanisms and explore the distribution of chemical elements on the formed coating layers, a Scanning Electron Microscope (SEM) with an X-ray Energy Dispersion Analyzer (EDAX) was employed. At low load values, mild wear by plowing and polishing of surfaces occurs. At high loads, the antiwear additives can be stimulated by temperature in such a way to cause an excessive chemical attack on the surfaces which results on pitting wear that may be changed to delamination wear. An inverted behavior, respect to the response to ASTM VE engine test sequence, possibly due to the different operation conditions and chemical environment predominant on the laboratory and engine bench tests, is reported and explained.