Superlubricity is a new area in tribology,in which the slide friction coefficient is about 1/1000 to 1/100 of the general ones.Since the concept of superlubricity was proposed,it has attracted more and more attentions from researchers in fields of tribology,physics,chemistry,materials,etc.Many significant progresses have been made during the last two decades in experimental studies on superlubricity.In the present work,the recent advancements in solid superlubricity and liquid superlubricity are reviewed and the lubricating mechanisms of different superlubricity systems are discussed.Finally,the problems on the superlubricity mechanism and the development of superlubricity in the future are addressed.
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.
