Formation and Characterization of Tribofilms

Fundamentals of tribofilm formation and their properties were studied. In order to understand the effects of lubricants on tribofilms, four base oils were investigated. Lubricants include castor oil, polyethylene glycol, mineral oil, and margarine. These oils were chosen based on their molecular structure, polarity, utility, and biodegradability. Experiments were conducted using a ball-on-disk tribometer to form tribofilms. Surface characterization was carried out using a stylus profilometer, a scanning electron microscope, and a transmission electron microscope. Results showed that oils with high polarity such as castor oil enhanced the formation of a transfer layer on the steel surface, whereas nonpolar oils such as mineral oil failed to do so. Oils with high polarity act as effective base oils to prevent metal hardening and bond debris particles to the metal surface. Oils with nonpolar components, on the other hand, generate abrasive nanoparticles during rubbing. Experiments with margarine at elevated temperature resulted in the formation of a hard and thick tribofilm. An adsorption model is illustrated to highlight the effects of lubricant molecules.