www.elsevier.com/locate/jmbbm Available online at www.sciencedirect.com Research Paper Fabrication and deformation behaviour of multilayer Al 2 O 3 / Ti/TiO 2 nanotube arrays S. Baradaran a,n , W.J. Basirun b,d , E. Zalnezhad a , M. Hamdi c , Ahmed A.D. Sarhan c , Y. Alias b a Department of Engineering Design and Manufacture, Faculty of Engineering University of Malaya, 50603 Kuala Lumpur, Malaysia b Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia c Center of Advanced Manufacturing and Material Processing, University of Malaya, 50603 Kuala Lumpur, Malaysia d Nanotechnology & Catalysis Research Centre (NanoCat), Institute of Postgraduate Studies, University Malaya, 50603 Kuala Lumpur, Malaysia article info Article history: Received 24 September 2012 Received in revised form 24 January 2013 Accepted 26 January 2013 Available online 9 February 2013 Keywords: Magnetron sputtering Adhesion TiO 2 nanotube Anodizing Nanoindentation abstract In this study, titanium thin films were deposited on alumina substrates by radio frequency (RF) magnetron sputtering. The mechanical properties of the Ti coatings were evaluated in terms of adhesion strength at various RF powers, temperatures, and substrate bias voltages. The coating conditions of 400 W of RF power, 250 1C, and a 75 V substrate bias voltage produced the strongest coating adhesion, as obtained by the Taguchi optimisation method. TiO 2 nanotube arrays were grown as a second layer on the Ti substrates using electrochemical anodisation at a constant potential of 20 V and anodisation times of 15 min, 45 min, and 75 min in a NH 4 F electrolyte solution (75 ethylene glycol: 25 water). The anodised titanium was annealed at 450 1C and 650 1C in a N 2 gas furnace to obtain different phases of titania, anatase and rutile, respectively. The mechanical properties of the anodised layer were investigated by nanoindentation. The results indicate that Young’s modulus and hardness increased with annealing temperature to 650 1C. & 2013 Elsevier Ltd. All rights reserved. 1. Introduction Bioceramics have recently become one of the most important biomaterials used for implants. They are the type of material most compatible with the human body due to chemical similarities that facilitate their direct bonding to bone. According to their level of interaction with living tissue, bioceramics can be divided into inert and active types. Alumina (Al 2 O 3 ) is a type of inert bioceramic utilised in orthopaedic implantation because of its good mechanical properties (high strength, high fracture toughness) and good compatibility. In addition, it is employed in the fabrication of bone plates, screws, and femoral heads and widely applied in total hip joint and knee replacement (Liu, 2007; Velmurugan et al., 2010; Youn et al., 2011). Over the last few decades, implant coating has found a wide array of applications. The thin-film coating of implant surfaces can be performed by various methods, including plasma spraying, electrophoresis, dipping, electrochemical deposition, pulsed laser deposition, ion beam dynamic mix- ing, and ion beam deposition (Oh et al., 2005; Raja et al., 2005; Kar et al., 2006; Best et al., 2008; Wang et al., 2008; Kodama et al., 2009; Roy et al., 2010; Wang and Luo, 2011). Some of these methods have severe limitations such as poor 1751-6161/$ - see front matter & 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jmbbm.2013.01.020 n Corresponding author. Tel.: þ601 7283 8175; fax: þ603 7967 5330. E-mail address: saeid_baradaran@yahoo.com (S. Baradaran). journal of the mechanical behavior of biomedical materials20 (2013) 272–282