Evolution of the nano-scale mechanical properties of tribofilms formed from low- and high-SAPS oils and ZDDP on DLC coatings and steel

The evolution of the nano-mechanical properties of tribofilms formed in steel/steel, steel/a-C:H and steel/Si-DLC contacts lubricated with two commercial oils containing different amounts of SAPS additives (E6 and E7 grade) and a mineral base oil containing ZDDP additive were examined in this investigation for two very different time periods. An atomic force microscope (AFM) was used in different modes to measure the topography, film thickness and stiffness, while the nano-hardness was measured with a nano-indenter. In addition, FTIR microscope was used on selected samples to explain some of the tribofilm׳s mechanical modifications with chemical changes. The results have shown that the tribofilm׳s evolution and growth are very much surface and additive dependent, and are different for steel and DLC coatings.