Synergistic effect of a coating and nano-oil lubricant on the tribological properties of friction surfaces

Abstract

In this study, we evaluated the tribological properties of grey cast iron (GC200) surfaces with and without MoS2 coating that were lubricated with either mineral oil or mineral oil in which fullerene nanoparticles were dispersed (i.e., nano-oil), by using a disk-on-disk type tribotester. A series of friction tests were performed using the disk-on-disk type tribotester under various normal forces, and the friction coefficient and friction surface temperature were monitored simultaneously. First, we observed that the friction coefficient of the GC200 surface that has a MoS2 coating and is lubricated with mineral oil was 32% lower than that of the GC200 surface without a MoS2 coating. Second, we found that the friction coefficient of GC200 surfaces lubricated with nano-oil was approximately 74% lower than that of GC200 surfaces lubricated with mineral oil. This suggested that the effectiveness of nano-oil lubrication in reducing the friction between GC200 surfaces is considerably higher than that of MoS2 coating or mineral-oil lubrication. In order to examine the effects of both the coating and nano-oil lubrication, friction tests for MoS2-coated GC200 surfaces under nano-oil lubrication was performed. We observed the following: (i) the friction coefficient of MoS2-coated GC200 surfaces lubricated with nano-oil were approximately 82% lower than that of uncoated GC200 surfaces lubricated with mineral oil; (ii) the nano-oil lubrication even tended to prevent the coating from peeling off, presumably because the fullerene nanoparticles added in the mineral oil acted as ball bearings. These observations suggested that the presence of a coating on friction surfaces and the addition of nanoparticles in mineral oil lubricant have a synergistic effect in significantly reducing the friction between friction surfaces.