Tribological Characteristics of GNPs and HNTs as Lubricant Additives in an Aluminum-Based Hybrid Composite-Steel Contact

Tribological performance comparison of Graphene nanoplatelet and Halloysite clay nanotube-based nanolubricants in an aluminum-based hybrid composite/steel tribo-contact was addressed by suspending nanoparticles in concentrations of 0.025, 0.05, 0.1 and 0.5%wt within SAE 5W40 motor oil. Dispersion stability and thermophysical properties of the designed nanolubricants were also evaluated. In order to perform tribological experiments by using a pin-on-ring configuration tribometer at various loads and rotation speeds, a hybrid composite was fabricated by powder metallurgy-extrusion method and characterized. The lubrication regime was characterized using stribeck curves and minimum film thickness. The worn surfaces morphology of the pin materials were characterized by Scanning electron microscopy images, Energy-dispersive X-ray spectroscopy and surface roughness measurements. The obtained highest friction coefficient and wear rate reductions were 40 and 36% with 0.5%wt Graphene nanoplatelet, and 25 and 10% for 0.1%wt Halloysite clay nanotube-based nanolubricants, respectively, during a mixed lubrication regime. The wear mechanism on the worn surface of the hybrid composite was predominantly abrasive with plastic yielding and delamination. Scanning electron microscopy images, Energy-dispersive X-ray spectroscopy and surface roughness measurements confirmed the Graphene nanoplatelet and Halloysite clay nanotube deposition on the worn surfaces and the formation of tribo-films that protect the sliding contacts.