Investigation of the tribological properties of nano-scaled ZrO2 and CuO additive in automotive lubricants

Abstract

Abstract To improve the fuel efficiency and the lifetime of the internal combustion engines, the lubricants and their additives have to be developed further. One of the possible future engines lubricants can be the nano-sized ceramic particles, which can provide positive tribological properties also in the presence of non-metallic surface materials. This paper presents the results of investigations with the help of ZrO2 and CuO nano-sized ceramic particles. To define the tribological properties of these additives, lubricant samples with different additive-concentrations were prepared and tribologically analysed. The frictional losses of these lubricant samples were analysed by a ball-on-disk sliding friction machine. The worn surface on the test specimens was analysed by different high-resolution microscopes. To define the functional mechanisms of the nano-additives, the worn surfaces were investigated by high resolution scanning electron microscopes. The ZrO2 additive has experimentally shown an excellent wear reduction property (over 40% wear reduction compared with the neat Group 3 base oil) at the optimum mixing concentration of 0.4wt%. Both frictional and wear reduction properties could be determined at the application of CuO additive (15-15% friction coefficient and wear scar diameter reduction) at its optimum concentration (0.5wt%). A copper-yellow layer can be seen on the worn surface of the disc specimens with CuO, which indicates the mechanism of chemical transformation to elementary copper from the cupric-oxide nanoparticle and this elementary copper can be melted on the surface, because of the applied high temperature and high loads during the experiments.