Investigation of Rheological Parameters of Lubricants and Contact Fatigue Behavior of Steel in the Presence of Cu Nano-Particles

摘要

Rheological properties of lubricants determine their flow behavior. Rheological parameters like viscosity index (VI), dynamic viscosity, shear stress and strain rate are influenced by dispersing Cu nanoparticles in them. This not only enhances the rheological properties of the lubricants, influences the contact fatigue behavior of steel also due to improved adhesive properties. Synthesis of new materials and additives is a technological marvel of Modern Tribo Chemistry that helps enhance the physicochemical and rheological properties of the lubricants and also enhances the contact fatigue behavior of materials. In order to study the effect of Cu nanoparticles on the rheological properties of lubricants two commercially available blended lubricants were selected as base oils with synthetic engine oils of SAE grades 5W40. They were dispersed with 0.2% of nano-Cu by weight. Physicochemical properties of oils were determined using standard ASTM and IS procedures. The experimental investigations were performed on four-ball sliding contact geometry to assess the anti-friction and anti-wear behavior. Rheological parameters were evaluated using rheometerPhy-sica MCR 301 from Anton-Paar Austria. Contact fatigue tests were also conducted on four ball fatigue tester using standard ASTM procedure. A significant reduction in friction and wear to the order of less than 13% has been observed for the 0.2 wt% of Cu nano-particles showing enhanced tribological performance of the base oils. Cu nanofluids form boundary films on the metal surfaces which help enhance the tribo performance by reducing friction and wear as confirmed by The SEM and EDX analysis. Also the surface topography of the worn out of used test specimens revealed smooth sliding wear against the severe wear by the base oils. Rheological data reveal that tested Cu nano-fluids behaved as non- Newtonian at low shear rates at all temperatures and at higher shear rates behaved as Newtonian fluids. On plotting the Weibull curves and survival probability curves it was observed that the nano lubricants showed much improved rolling contact fatigue life with an enhancement of L10 life from 16 to 61% and L90 life from 18 to 118%. Characteristic life also showed an improvement upto 117.6%. Moreover survival probability of rolling contacts also showed an improvement in the presence of nano-Cu particles.