Investigation of ultra-low friction between self-mated Si3N4 in water after running-in

The aim of this work was to determine the mechanism of ultra-low friction between a self-mated Si3N4 pair lubricated with water after running-in. The key to solving this problem was to determine the lubrication regime of the interface under ultra-low friction conditions. According to the Stribeck curve, the variations of friction coefficient with load and velocity were measured to evaluate the hydrodynamic effect; and the variation under different lubricating oils was examined to investigate the influence of viscosity and eliminate the influence of any tribochemical reaction between Si3N4 and water. Surface wear after a long-duration friction test under ultra-low friction conditions was also evaluated. It was found that the ultra-low friction mechanism was attributed to a pure hydrodynamic effect.