Effect of Graphene Nanoplates Dispersed in Ethanol on Frictional Behaviour of Tool Steel Running Against Uncoated and DLC-Coated Tool Steel

Abstract

Friction tests conducted between two tool steel surfaces sliding under boundary-lubricated condition in ethanol containing 5 × 10−4 wt% graphene nanoplates (GNP) under the boundary-lubricated condition showed a low coefficient of friction (COF) of 0.18, compared to 0.31 without the addition of GNP, and generated graphene incorporating tribolayers at the contact surfaces. Oxidation of the steel surfaces at high-sliding cycles increased the COF. When a diamond-like carbon (DLC)-coated counterface was used against the tool steel in GNP-containing ethanol a low steady-state COF (µS) of 0.06 was observed, and the wear rates of the DLC-coated steel were decreased by 70% compared to sliding against an uncoated tool steel counterface. Tribolayers that consisted of graphene flakes formed on top of and within the iron oxide layers that were generated on the steel surfaces. The graphene layers were deformed and damaged according to Raman spectroscopy. Cross-sectional high-resolution TEM revealed that sliding contact caused bending and occasional fragmentation of graphene layers. The graphene layers deposited on top of the tribololayers provided low friction.