Lubricating reaction products on TiN coatings during sliding wear in phosphoric acid

The debris structure influences the tribological behaviour of TiN coatings sliding against corundum. During sliding wear in environmental air, self-lubricating debris can be generated depending on the conditions. The (micro)structure of the debris varies with the relative humidity, temperature, mechanical attrition and temperature. In this paper, the wear rate and the friction of TiN coatings are compared with uncoated tool steel substrates sliding against corundum in: humid air, demineralised water, and phosphoric acid (0.02 M H3PO4). Differences in the tribological behaviour are explained in terms of the interaction with the environment. In phosphoric acid, TiN coatings sliding against corundum show very low friction forces and wear rates due to the formation of a lubricating gel.