Tribological behavior and lubricating mechanism of Si3N4 in artificial seawater

Abstract Tribological behavior and lubrication mechanism studies on Si3N4 sliding against two different materials (stainless steel and PEEK) under different normal loads in artificial seawater condition were conducted by pin-on-disc wear test, SEM, EDS and XPS techniques. With increasing load from 10 N to 30 N, the friction coefficient of Si3N4/stainless steel sliding pair increased from 0.48 to 0.72. Whereas, the friction coefficient of Si3N4/PEEK sliding pair decreased from 0.27 to 0.07. However, the wear rates of these two sliding pairs were consistent. When Si3N4 slid against stainless steel, the formation of the tribofilm contributed to reduced friction coefficient and wear at a low load of 10 N. The Si3N4 sliding surface was protected by the tribofilm and smoothed. However, with increasing load, the film could not withstand the pressure. Hence, the direct contact of Si3N4/stainless steel sliding pair was developed and furrows on their solid surfaces occurred, leading to the increase of the friction coefficient. When Si3N4 slid against PEEK, a good tribological performance was achieved in seawater condition, which was possibly attributed to the viscoelasticity of PEEK, seawater cooling process, water adsorption of PEEK, and tribochemical reaction of Si3N4. Besides, the relation between the friction coefficient and the normal load could be expressed by a classical equation f = K N ( n − 1 ) .