Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Effect of graphene film on laser textured alumina surface characteristics B.S. Yilbas a,b, ⁎ , A. Ibrahim b , H. Ali b , M. Khaled c , T. Laoui b a Center of Excellence in Renewable Energy, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia b ME Department, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia c CHEM Department, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia ARTICLE INFO Keywords: Laser texturing Aluminum nitride Graphene film Hydrophobicity Friction coefficient ABSTRACT Laser gas assisted texturing of alumina surface is considered and the effects of graphene film on the properties of the textured surface are examined. Since laser texturing under the high pressure nitrogen gas jet environments results in formation of aluminum nitride compounds, free energy of the textured surface reduces considerably. The mismatch between the surface free energies of the graphene film and the laser textured surface makes it difficult to transfer the graphene film on the textured surface without rippling and edge defects. A graphene oxide film is formed at the textured surface prior to transferring of the graphene film. The characteristics of the laser textured and the graphene transferred surfaces are assessed using the analytical tools including electron and atomic force microscopes, Raman spectroscopy, X-ray diffraction, and UV visible absorbance spectroscopy. Surface hydrophobicity of the graphene transferred and laser textured surfaces is determined incorporating the water droplet contact angle measurement technique. Friction coefficient of the graphene transferred and laser textured surfaces are measured using the scratch tester. It is found that laser texturing results in hydrophobic characteristics because of the micro/nano size pillars formed at the surface and reduced surface energy due to aluminum nitride compounds. Transferring of the graphene film on to the laser textured surface reduces both the water droplet contact angle and the contact angle hysteresis. The presence of the graphene film reduces the friction coefficient and it does not alter notably the absorption characteristics of the laser textured surface. 1. Introduction Graphene has two-dimensional atomic structure with excellent properties such as high mechanical strength, superior electrical and thermal conductivities, and almost nearly optical transmittance. Graphene finds wide applications in electronic circuits [1], medicine [2], photovoltaics [3], and engineering fields [4]. Graphene film can improve surface characteristics, such as friction coefficient and thermal conductivity, of ceramics. On the other hand, the hydrophobic char- acteristics of the ceramics, such as alumina, surface can be improved through laser gas assisted texturing [5]; however, the textured surface has high friction coefficient and some surface defects such as micro-size cracks, which limit the practical applications of the treated surface in bearing applications. Although laser texturing of surfaces has several advantages over the conventional methods, such as local treatment, fast processing, precision of operation and low cost, high thermal stresses are developed in the surface region while causing formation of the micro/nano size cracks. The presence of micro-cracks has adverse effects on mechanical and optical properties because of the possible delamination of the textured surface through the micro/nano cracks networks. However, graphene coating at the surface covers the crack sites and minimizes the mechanical defects at the surface. Consequently, investigation of the effects of graphene layer, which is formed on the top of the laser textured alumina surface, on the properties of the laser textured surfaces becomes essential. Considerable research studies were carried out on laser texturing of ceramic surfaces. Laser-induced deposition of alumina ceramic coating on stainless steel was investigated by Adraider et al. [6]. They showed that laser irradiation of dry alumina films led to the deposition of crystalline alumina coating in α-Al 2 O 3 form on substrate surface. In addition, the mechanical properties of the alumina-coated surface were significantly improved and reached the same level as pure α-alumina ceramic. A pulsed laser deposition of alumina thin films was carried out by Boidin et al. [7]. They demonstrated that the use of argon gas during the deposition process resulted in grainy structure of the thin films and decrease of the refractive index of the alumina layers was observed within the 300–7500 nm spectral range when increasing argon pres- sure. Laser gas assisted nitriding and sol–gel coating of alumina http://dx.doi.org/10.1016/j.ceramint.2016.10.169 Received 2 October 2016; Received in revised form 22 October 2016; Accepted 24 October 2016 ⁎ Corresponding author at: Mechanical Engineering Department and Center of Excellence in Renewable Energy, King Fahd University of Petroleum & Minerals, Dhahran, Saudi Arabia. E-mail address: bsyilbas@kfupm.edu.sa (B.S. Yilbas). Ceramics International xx (xxxx) xxxx–xxxx 0272-8842/ © 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Available online xxxx Please cite this article as: Yilbas, B.S., Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.10.169