A fuzzy logic predictive model for better surface roughness of Ti–TiN coating on AL7075-T6 alloy for longer fretting fatigue life

Keywords: AL7075-T6 alloy Ti–TiN coating PVD magnetron sputtering Surface roughness Fuzzy logic Fretting fatigue a b s t r a c t In this study, the fretting fatigue resistance of AL7075-T6 alloy is investigated using surface treatment Ti–TiN multilayer coating by physical vapor deposition (PVD) magnetron sputtering technique. A fuzzy logic model was established to forecast the surface roughness of Ti–TiN coating on AL7075-T6 with respect to changes in the input process parameters of DC power, temperature, DC bias voltage, and nitrogen flow rate. The results indicate an agreement between the fuzzy model and experimental results with 95.349% accuracy. The fretting fatigue lives of Ti–TiN-coated specimens with the lowest surface roughness resulting from fuzzy logic were enhanced by 18% at low cyclic fatigue, while at high cyclic fatigue the result was reversed. Lightweight and high-strength aluminum alloys such as 7075 are widely utilized in aircraft engines, fuselage and automobile parts. Aluminum alloys themselves do not provide adequate mechanical strength for structural parts. Therefore, enhancing surface properties is vital in practical applications, particularly when aluminum is in contact with other components [1]. Ceramic coatings like TiN, CrN, and SiC are possibly effective in raising surfaces hardness, corrosion and wear resistance. However, coatings used for aluminum alloys via old-fashioned techniques such as hard anodizing, glazing and thermal spaying, are provided with little support from the underlying material besides the inadequate adhesion strength, decreasing their durability [2,3]. Fretting fatigue is a phenomenon which occurs when two components are in contact with each other and one or both are subjected to a cyclic load, often resulting in damage which may cause premature component failure. Ti–TiN coating applied by PVD technique is a method of improving the hardness of Al7075-T6 surface by reducing wear and extending fretting fatigue service life [4–6]. The formation of TiN coating on the surface of materials is among the most effective techniques of improving material wear resistance. However, the characterization of surface topography is imperative in applications including abrasion, wear, and lubrication. Surface hardness and roughness are important when identifying the performance of a coated surface [7,8]. High surface quality is essential in achieving lower surface roughness, which affects the practical characteristics such as friction, fretting fatigue, wear, and light reflection [9]. The surface rough-0263-2241/$-see front matter Ó 2013 Elsevier Ltd. All rights reserved.