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This work uses synchrotron radiation XANES and XPS measurements to investigate the structure of ZDDP tribofilms formed from lubricants contaminated with anhydrous and hydrated ethanol (5%wt). The tribofilms were formed at 40 °C from PAO8 lubricant containing only ZDDP additive onto carbon steel specimens using sliding tests, cylinder-on-flat configuration (line contact) under boundary lubrication. Ethanol increased friction as well as surface damage, detected by an increase in relative porous area. Angle-resolved measurements (15°, 45°, 90°) helped detecting differences along the thickness of the tribofilm. The amount of long-chain phosphates apparently reduced with ethanol, leading to reduced wear performance. The sulphides in the tribofilms were richer in Fe in the presence of ethanol, also indicative of more severe wear.

Microabrasion-corrosion tests were carried out to investigate how small changes in dilution affect abrasion-corrosion resistance of Ni–Cr PTA welded deposits onto carbon steel. For each specimen, corrosion tests, microabrasion tests and combined microabrasion-corrosion tests were conducted. Potentiodynamic corrosion tests under aerated conditions used three different electrolytes. Abrasion resistance was evaluated using a fixed-ball microabrasion test rig, for slurries of SiO2 in distilled water (20 wt%). Microabrasion-corrosion tests used SiO2 slurries for the same electrolytes used in the corrosion tests under potentiodynamic conditions. For the most aggressive electrolyte (NaCl + H2SO4 solution) it was possible to identify small variations in current density with dilution in the microabrasion-corrosion tests, whereas no significant differences were identified for the other electrochemical variables. However, as a general trend, all deposits presented high abrasion-corrosion resistance, evidencing that small variations in dilution do not compromise their performance for the conditions tested. As expected, the wear coefficients measured under microabrasion-corrosion conditions were higher than under pure microabrasion conditions. On the other hand, friction coefficients for microabrasion-corrosion were lower when compared with conventional microabrasion tests for all the slurries tested. This was apparently due to how the passive film affects particle entrainment during the tests.

The influence of surface topography on lubricant film thickness has been investigated for the reciprocating sliding of patterned plane steel surfaces against cylindrical counterbodies under conditions of hydrodynamic lubrication. Patterns of circular depressions, grooves and chevrons were used, and the fractional area coverage, depth, width and sliding orientation relative to the texture were systematically varied. Textured samples with features much larger than the elastic contact width gave film thicknesses, which were smaller than those for non-textured samples. This effect was more significant for larger features. For patterns composed of circular pockets, maximum film thickness was achieved for an area coverage fraction f≈0.11. Chevron patterns pointing along the sliding direction gave higher film thicknesses than those pointing across. For an area coverage ratio of ca. 0.06, maximum film thickness was achieved for a feature depth to width ratio of about 0.07. Among the patterns investigated, chevrons were the most effective and grooves the least effective in increasing hydrodynamic film thickness.