Study on the Lubrication Performance of Graphene-Based Polyphosphate Lubricants in High-Temperature Steel–Steel Friction Pair

In the study, a hybrid lubricant was prepared by introducing graphene into a polyphosphate lubricant. In the tribological test of a steel/steel friction pair at the high temperature of 800 °C, the addition of a small proportion of graphene significantly enhances the lubrication performance of polyphosphate at elevated temperatures. The coefficient of friction and the wear were obviously held down while the surface quality of the high-temperature friction pair was enhanced effectively with the graphene-strengthened polyphosphate lubricant, compared with the dry sliding condition. Through scanning electron microscopy and Raman spectroscopy analysis, the formation mechanism of tribofilm and the antiwear performance of the hybrid lubricant are further explained. This lubricant effectively combines the advantages of both; the combination of polyphosphate melted at elevated temperature with graphene and metal surfaces ensures the self-sealing of the friction contact area and brings better high-temperature oxidation resistance. At the same time, the presence of graphene provides excellent strength to the friction film and ensures the anti-wear and wear-resistant performance of the lubricant at high temperatures.