Tribology behaviour of graphene-modified nanostructured Al2O3/3 % TiO2 coatings under boundary and mixed lubrication conditions
K. A. Habib, D.L. Cano, Julio Serrano Mira, E. Rayón, José V. Abellán‐Nebot, S. Dosta
Abstract
This study is focused on the preparation of a self-lubricating coating via thermal spraying. This coating was designed to control friction and lubrication in both boundary lubrication (BL) and mixed lubrication (ML) regimes. We aimed to compare the tribological behaviour of nanostructured Al 2 O 3 /3 % TiO 2 and modified nanostructured Al 2 O 3 /3 % TiO 2 incorporating 3 % GNPs coatings deposited by Oxygen-Fuel (OF). The critical conditions for the transition from BL to ML were experimentally studied using a fundamental tribological concept known as the Stribeck curve. A lubricating film consisting of detached GNPs, Al 2 O 3 nanoparticle debris, and a conventional lubricant effectively covers the surface material and improves the mechanochemical interactions between the surface material and lubricating oil, thereby enhancing the tribological performance. The introduction of GNPs is found to play an effective role in the lubrication regime, leading to an increase in microhardness, a decrease in the friction coefficient and wear volume of the Al 2 O 3 /3 % TiO 2 coating, and the steel counterpart disc. It noticeably improved the critical load-carrying capacity at different speeds during the transition from BL to ML regimes. The tribo-layer formed on the worn surfaces controls the tribological properties of the Al 2 O 3 /3 % TiO 2 + 3 % GNPs coatings. • Adding graphene to nanostructured Al 2 O 3 /3 % TiO 2 reduces porosity and enhances microhardness. • Lubrication regime parameters can be computed by including load-carrying capacity in tribology studies. • The effect of load-carrying capacity on lubrication regimes is discussed.