Third Body Formation on Self-Lubricating Multicomponent Coatings Tested under High Temperature Sliding Wear Conditions

Self-lubricating multicomponent coatings are commonly used to reduce wear and friction in different conditions. Particularly, the PS series consist of coatings with soft metals and halides as solid lubricants, designed to reduce wear and friction in temperatures ranging from room temperature to 900°C. The wear rate and the friction coefficient as a function of temperature for these coatings are often found in literature, but an in-depth evaluation of third body formation and evolution during wear is not fully explored. In this paper, two of such coatings, NiCr-Cr₂O₃-BaF₂/CaF₂-Ag (PS304) and NiMoAl-Cr₂O₃-BaF₂/CaF₂-Ag (PS400), were sprayed by Atmospheric Plasma Spray. However, a low deposition efficiency and the lack of components with high melting point was observed. By adding a secondary gas, the deposition efficiency was improved with all the components being melted during spray. Then, wear tests were performed with these coatings under different temperatures (room temperature, 200, 350°C). The tribofilm formed in these different conditions were characterized in terms of morphology, chemical composition and mechanical properties and correlated with the wear behavior of these materials.