Temper Colours of Wear Particles

ABSTRACTIn the present work, wear particles, retained by oil filter of an internal combustion engine, were examined by optical microscope to reveal details of size, shape and quantity of particles. The temperature of the moving surfaces inside engines can be determined by observing the temper colours of the wear particles. Because of the electronic mechanism of oxidation, the optical interference of the oxide film formed on the surfaces of wear particles can give rise to the appearance of colours depending on the thickness of the film. The rate of oxidation and therefore the thickness of the oxide film is determined by the crystallographic orientation of the substrate metal. Based on the observations in the present work, it can be suggested that the sliding surfaces of the engine were suffered from severe micro-cutting process. The presence of the surface striations confirms the evidence of abrasive wear, where the rise of temperature might be attributed to the severe friction and the micro-cutting process caused by excessive abrasive particles contaminated in the lubricant and embedded in the sliding surfaces. The change of the temper colours of wear particles might be from temperature rise caused by extra friction as well as the abrading action of abrasive particles into the sliding surfaces.