Preparation and tribological properties of multi-layer graphene/silicon dioxide composites-based solid lubricant coatings at elevated temperatures

The solid lubricating coatings have an important role in hot metal forming. However, traditional lubricants cannot be applied to the harsh working conditions. In this investigation, the novel solid lubricant coatings including multi-layer graphene (MLG)/silicon dioxide (SiO ) composites and sodium metaphosphate phosphate were prepared. The high-temperature tribological properties of the solid lubricant coatings were investigated by friction and wear tester. The experimental results showed that SiO nanoparticles were evenly grafted by sol-gel method on the surface of MLG, forming MLG/SiO composites. MLG/SiO composites presented excellent thermal stability at 800°C. In the range of 400-800°C, the average coefficients of friction (COFs) were decreased from 0.3936 to 0.3663, and then increased from 0.3663 to 0.4226. Based on the analysis of wear scar, the lubrication mechanisms of the solid lubricating coatings were proposed. The low interlayer shear of MLG and the ball bearing of SiO nanoparticles are the main reason for the reduction of COFs. In addition, the tribo-chemical reaction film formed on the frictional interface could protect the contact surfaces from severe damage. The findings would be beneficial for developing novel lubricants for hot metal forming process.