IMPROVEMENT IN TRIBOLOGICAL PROPERTIES OF CHROMIUM-OXIDE COATING AT HIGH-TEMPERATURE BY SOLID LUBRICANTS

The aim of the investigations was to improve the tribological properties of chromium oxide (Cr2O3) coating for applications in heat engines at high temperatures. The experimental results show that the solid lubricants CaF2 and BaF2 in composite coatings can reduce and stabilize the friction coefficient, decrease the wear rate, prevent surface damage and improve the load capacity of Cr2O3 coating at 425-degrees-C in air. In tribotests at 0.2-1.0 MPa it appears that the optimal solid lubricant content is around 14%-21% for Cr2O3-CaF2 coatings and 20%-31% for Cr2O3-BaF2 coatings. Auger electron spectroscopy and energy-dispersive spectroscopy analyses show that the friction coefficient is correlated with the amount of solid lubricant in contact areas: the friction coefficient decreases with solid lubricant content if it is less than 2%-4%, then stabilizes at about 0.20-0.25.