Effect of CuO and Al2O3 nanoparticle additives on the tribological behavior of fully formulated oils

• GL-4 and PAO 8 nanofluids were characterized for tribological properties.
• Al2O3 nanoparticles acted as an abrasive, showing a detrimental effect on both oils.
• All tribological properties increased with the addition of CuO nanoparticles.
• Nanoparticles may fill surface roughness decreasing friction and wear.

Lubrication is essential for the advancement of energy efficient modern industries. Lubricants are widely used in industry to minimize friction and wear between tools and moving components. Additives are utilized as common lubricants reinforcement in order to achieve overall improved tribological properties. This study presents and discusses the tribological properties of friction, wear, and extreme pressure of two synthetic lubricants: GL-4 (SAE 75 W-85), a fully-formulated oil; and Poly-alpha olefin 8 (PAO 8) base oil. These lubricants were doped at various filler concentrations (0.5, 1.0, and 2.0 wt%) of CuO and Al2O3 nanoparticle additives. Anti-wear tests were performed with an Optimol SRV 4 tester, according to ASTM D5707; extreme pressure tests were performed with a T-02 four-ball tribotester. Wear scar diameters (WSD) were characterized by optical microscopy, scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS). Anti-wear results showed a decrease of up to 18% and 14%, on coefficient of friction (COF) and WSD with 2 wt% CuO/PAO 8. The load carrying capacity (poz) of GL-4 and PAO 8 increased by ~14% and ~273%, respectively, with the addition of CuO nanoparticles. However, the incorporation of Al2O3 nanoparticles was not as effective, showing an increase of up to 18% and 12% on poz for GL-4 and PAO 8, respectively.