Friction and wear performance of olive oil containing nanoparticles in boundary and mixed lubrication regimes

In the recent years of lubrication development, vegetable oils have been considered as potential candidates for improving the overall tribological performance in comparison to the mineral oils. However, certain issues like oxidation stability restrict their use as lubricating oils under wide range of operating conditions. In this research work, epoxidation of the olive oil was carried out to improve its oxidation stability. Further, the effect of nanoparticles in different concentrations was evaluated to study the friction and wear behaviour of epoxidised oil. Tribological testing was performed for a pin on disc configuration for Liquid metal alloy/steel contacts. LM alloy was selected owing to its increased use in cylinder liner applications. Stribeck curves for virgin oil, epoxidised oil and the oil containing nanoparticles were generated in the boundary and mixed lubrication regimes. It was observed that epoxidised oil showed better lubricating characteristics than virgin olive oil. This is due to the formation of stable polymeric film through -O- cross linking on the surface. A further improvement on the addition of nanoparticles was also obtained, wherein it was observed that 0.5 wt% concentration of nanoparticles exhibit minimum coefficient of friction. SEM analysis of the worn out samples was carried out to understand the possible mechanism of wear and it was observed that accumulation of nano particles in valleys and the formation of a thin film at the interface appears to be the main reason for the improved tribological properties of the lubricating oil.