Extreme pressure lubrication between ceramic and bearing steel with liquid metal

The behaviors of extreme pressure (EP) lubrication for tribo-pairs between silicon nitride (Si3N4) and bearing steel (GCr15) with the lubricants of gallium-based liquid metal (GBLM) and Gear Oil (GO) have been studied on the four-ball test (FBT) machine. The experimental results demonstrated that temperature with GBLM directly measured at the bottom of FBT liquid pool was linearly proportional to the applied load and rotating speed, which was consistent with the variation trend of interfacial temperature simulated by COMSOL. These experimental and simulated results have identified that GBLM lubricant could significantly reduce interfacial temperature and was more suitable for EP lubrication due to its high thermal conductivity than that of GO. Moreover, some experimental results showed that the wear scar diameter with GBLM was smaller than that with GO under the same EP working condition. It has been proved that different materials in Si3N4-GCr15 tribo-pairs did not weld together even in a hard EP working condition. This work also indicated that the new ideas for synthesizing materials were urgent as the tribo-pairs and EP lubricants with high thermal conductivity, which could improve the reliability and feasibility of the EP working condition in the industrial field.