Friction Behaviour of Multilayered Graphene against Steel
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Friction Behaviour of Multilayered Graphene against Steel A. Banerji1, S. Bhowmick1, M.J. Lukitsch2 and A.T. Alpas1 1 Mechanical, Automotive and Materials Engineering, University of Windsor, 401 Sunset Avenue, Windsor, ON N9B 3P4, Canada. 2 Chemical Sciences and Materials Systems Laboratory, General Motors R&D Center, 30500 Mound Road, Warren, MI 48090-9055, U.S.A. ABSTRACT Frictional behaviour of multilayered graphene was studied in air with different relative humidity (RH) levels (10–52% RH). Pin-on-disk type sliding tests were performed and the running-in and steady state coefficient of friction (COF) values were measured against M2 tool steel counterface. On increasing the RH, multilayered graphene showed a reduction in steady state COF from 0.11 at 10% RH to 0.08 at 52% RH. The low steady state COF values observed in graphene could be attributed to the transfer layer formed on the M2 tool steel counterface. A sliding-induced structural change was observed in graphene transfer layers which could have facilitated the graphitic transfer layer formation. The multilayered graphene showed a lower steady state COF values at all RH compared to non-hydrogenated diamond-like carbon (NHDLC) which recorded a steady state COF of 0.47 at 10% RH and 0.25 at 52% RH. INTRODUCTION Graphene is a two dimensional monolayer of carbon atoms that serve as building blocks of graphite [1]. The nano and micro-scale friction behaviour of graphene is of interest and is currently being studied [2-4]. Lee et al. [2] demonstrated using friction force microscopy (FFM) experiments (25-50% RH) on mechanically exfoliated graphene that friction values of more than four layers of graphene was as low as that of bulk graphite while a monolayer graphene plane showed higher friction. Friction behaviour of graphene also depends on other factors such as graphene-substrate adhesion, as well as on environmental conditions. Kim et al. [3] found that the COF of CVD grown graphene was affected by the substrate as the graphene grown on Ni showed a low COF of 0.10 compared to graphene grown on Cu (COF = 0.20) under a normal load of 70 mN (33% RH). Berman et al. [4] reported a COF of 0.18 for ethanol processed graphene used as lubricant for steel vs. steel sliding in a dry N2 atmosphere. Bhowmick et al. [5] reported the role of humidity in determining the friction behaviour of multilayered graphene by performing macro scale experiments in air with different relative humidity (RH) levels (10–45% RH) against a Ti alloy counterface. It was shown that progressively lower friction values were observed when the RH of the atmosphere was increased, with the lowest COF of 0.11 reached at 45% RH which was attributed to the chemisorption of H and OH molecules in the graphene stacks [5]. Diamond-like carbon (DLC) coatings can improve the performance of the machining tools and dies by reducing the coefficient of friction (COF); minimizing adhesion to workpieces made of steel, aluminum, magnesium and titanium alloys [7-13]. However, the tribological properties of DLC coatings
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