Investigation of Corrosion Behavior of Ti/TiN Multilayers on Al7075 Deposited by High-Vacuum Magnetron Sputtering in 3.5
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JMEPEG https://doi.org/10.1007/s11665-018-3306-x
Investigation of Corrosion Behavior of Ti/TiN Multilayers on Al7075 Deposited by High-Vacuum Magnetron Sputtering in 3.5% NaCl Solution Esfandiar Molavi, Ali Shanaghi, and Paul K. Chu (Submitted March 9, 2017; in revised form September 7, 2017) Although Al 7075 has many favorable mechanical properties such as the large strength-to-weight ratio, the relatively poor corrosion resistance has restricted industrial applications. In this work, Ti/TiN as hard multilayered and nanostructured coatings are deposited on the relatively soft Al 7075 structure by highvacuum radio-frequency magnetron sputtering and the phase, structure, and morphology are investigated in details. The corrosion behavior is evaluated by electrochemical impedance spectroscopy in 3.5% NaCl at a pH of 7.5 for 1, 6, 12, 24, 36, 48, 60, and 72 h. At time points of 1, 6, 12, and 24 h, primary oxide layers and double layers are formed, but the corrosive medium penetrates the primary titanium nitride columnar structure. At longer time points of 24, 36, 48, 60, and 72 h, formation of stronger oxide and double layers leads to better corrosion resistance which is 14.8 times better than that observed from the uncoated substrate after immersion for 36 h. According to Rct, the corrosion resistances of the short and long immersion groups are 808.5-1984 and 808.5-1248 kX cm2, respectively, thereby confirming the effectiveness of the Ti/TiN coating against corrosion in comparison with the corrosion resistance of 84.3 kX cm2 observed from the uncoated Al 7075. The smallest corrosion resistance of 808.5 kX cm2 observed at the time point of 24 h is 9.6 times that of the uncoated substrate. Keywords
Al 7075, electrochemical impedance spectroscopy, high-vacuum radio-frequency magnetron sputtering, Ti/TiN hard multilayered nanostructured coating
1. Introduction Zinc and copper are the main alloying elements in Al 7075 which has strength comparable to that of many steel alloys, good fatigue strength, and surface machinability. However, formation of galvanic cells in corrosive media leads to relatively poor corrosion resistance (Ref 1). Deposition of metallic and ceramic coatings can improve the corrosion resistance and mechanical properties. In particular, titanium nitride is widely used in surface engineering due to the high chemical stability and hardness, excellent coating characteristics, good electrical properties, and environmental compatibility (Ref 2). However, TiN coatings do not adhere well to active metals such as aluminum. In addition, the columnar structure and pores in the coating allow penetration of corrosive ions and to overcome this hurdle, a titanium
Esfandiar Molavi and Ali Shanaghi, Materials Engineering Department, Faculty of Engineering, Malayer University, Malayer, Iran; Paul K. Chu, Department of Physics, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong, China; and Department of Materials Science and Engineering, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong,
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