Statistical optimization and fretting fatigue study of Zr/ZrO 2 nanotubular array coating on Ti–6Al–4V S. Baradaran a , E. Zalnezhad a, ⁎, W.J. Basirun b,c , A.M.S. Hamouda d , M. Sookhakian e , Ahmed A.D. Sarhan a , Y. Alias b a Department of Mechanical Engineering, 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 Department of Physics, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia d Mechanical and Industrial Engineering Department, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar e Nanotechnology & Catalysis Research Centre (NanoCat), University of Malaya, 50603 Kuala Lumpur, Malaysia abstract article info Article history: Received 11 February 2014 Accepted in revised form 16 July 2014 Available online xxxx Keywords: PVD magnetron sputtering Zirconium nanotube array Fretting fatigue Taguchi method Pareto ANOVA Herein, the fretting fatigue behavior of zirconium nanotube arrays on the surface of Ti–6Al–4V is studied. Initially, a thin film of pure zirconium (Zr) was deposited onto a Ti–6Al–4V substrate using physical vapor deposition (PVD) magnetron sputtering for the primary layer at varying DC power, temperature and substrate bias voltage values. To obtain higher adhesion strength, the Taguchi optimization method was used to estimate the optimum coating pa- rameters, while a Pareto ANOVA was employed to determine the significant parameters. The strongest coating ad- hesion, as determined by a scratch force test, was achieved at 300 W DC power, 200 °C and a 75 V bias voltage. Consequently, nanotubes were produced via Zr anodization in an NH 4 F electrolyte solution (95 glycerol:5 water) at different times and at a constant potential of 60 V (second layer). The fretting fatigue behavior of anod- ized samples annealed at 400 °C and 800 °C was investigated. The results indicate that the fretting fatigue life of the ZrO 2 nanotube-coated samples was significantly improved at low and high cyclic fatigue at an annealing temperature of 400 °C compared to the uncoated samples. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Metallic biomaterials used to replace and repair human body parts have attracted tremendous amounts of attention over the past two de- cades [1–3]. A large number of implant materials, such as bone plates, screws, dental implants, and artificial joints, which are utilized to a large extent in various medical applications, are made of titanium alloys because of titanium's excellent biocompatibility, low elastic modulus, and high corrosion resistance [4–7]. Unfortunately, the inferior wear re- sistance of such implants has motivated researchers to increase their focus on overcoming this issue [8,9]. Different aspects of biomedical ap- plications and the mechanical properties of biomaterials are crucial with respect to materials being applied as long-term in vivo implants [10–12]. The nonconformity between bone and the implant surface layer is among the reasons for mechanical failure, particularly in relation to the deteriorating modulus of elasticity [13]. Therefore, it is very im- portant to consider the mechanical properties of implant materials, es- pecially those used in orthopedic applications. Orthopedic implant instruments are often manipulated under fatigue conditions and occa- sionally fail due to monotonic loads, fatigue, and corrosion fatigue [14]. Thus, investigating the mechanical performance of titanium alloys, particularly plain and fretting fatigue life, is a significant factor regarding their use in biomedical applications [15,16]. Fretting fatigue is a phenomenon that can occur between two bod- ies, such as bone plates and screws [17,18]. According to a previous as- sessment, 74% of implants that fail in the femoral neck region and in the modular junctions do so as a result of fretting fatigue [19–22]. Through- out the past two decades, the fretting fatigue of titanium alloys has been significantly improved using surface modifications with various nitride coatings (TiN, ZrN and TiAlN) [21–24]. Nanostructured metal oxides, such as TiO 2 and ZrO 2 nanotubes, are hard and wear-resistant, which is why the use of nanostructured TiO 2 and ZrO 2 coatings is becoming the surface modification method of choice [25,26]. Zirconia nanotubes have several advantages, among which are their chemical and dimen- sional stability, good fracture toughness, Young's modulus similar to that of stainless steel, bending strength, excellent biocompatibility, and high resistance to corrosion by bodily fluids. Thus, zirconia coatings on titanium alloys result in a high adhesion strength and are widely used in medical applications [27,28]. Over the last few decades, various coating methods have been implemented by numerous researchers. The mechanical properties of coatings play a considerable role in biomedical implants, which is why selecting the best coating methods is a very important issue. To date, a variety of coating methods have been implemented, such as pulsed Surface & Coatings Technology xxx (2014) xxx–xxx ⁎ Corresponding author. SCT-19583; No of Pages 12 http://dx.doi.org/10.1016/j.surfcoat.2014.07.046 0257-8972/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat Please cite this article as: S. Baradaran, et al., Surf. Coat. Technol. (2014), http://dx.doi.org/10.1016/j.surfcoat.2014.07.046