Effects of antiwear additives on the friction and wear of Si3N4/steel sliding contacts

Si3N4-based ceramics have been used for machining cast iron at very high speeds. However, they have been found to be unsuitable for machining steel because of the severe wear of the ceramic cutting tools, which is thought to be mainly caused by the chemical dissolution of the ceramic in the chip at the high temperatures reached at the cutting edge. In this paper, a simulation test was carried out on a pin-on-disk tribometer in order to investigate the effects of two antiwear additives on the friction and wear of Si3N4/1045 steel sliding contacts. Sliding speeds 1.6 m s(-1) and 3.2 m s(-1) were used, respectively, the selected test load was 117.6 N. The test results show that lubricants containing antiwear additives used in this test could greatly reduce the friction coefficient and wear rate of Si3N4 ceramics. Scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction spectroscopy were used for the analyses of the worn surfaces. Tribochemical reactions about the additives occurred on the frictional surfaces, the tribochemical films formed on the rubbing surfaces improved the boundary lubrication conditions of the sliding contacts, the interdiffusion and adhesion between the rubbing surfaces were prevented or were greatly reduced.