Investigations of the superlubricity of sapphire against ruby under phosphoric acid lubrication

摘要

Abstract In this study, we address the superlubricity behavior of sapphire against ruby (or sapphire against itself) under phosphoric acid solution lubrication. An ultra-low friction coefficient of 0.004 was obtained under a very high contact pressure, with a virgin contact pressure up to 2.57 GPa. Related experiments have indicated that the load, sliding speed, and humidity of the test environment can affect superlubricity to some degree, so we tested variations in these conditions. When superlubricity appears in this study a thin film is present, consisting of a hydrogen bond network of phosphoric acid and water molecules adsorbed on the two friction surfaces, which accounts for the ultra-low friction. Most significantly, the wear rate of the sapphire and ruby in the friction process is very slow and the superlubricity state is very stable, providing favorable conditions for future technological applications.