Open Access. © 2017 B. Thangaraj and K. Mahadevan, published by De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License Electrochem. Energy Technol. 2017; 3:27ś34 Research Article Baskar Thangaraj* and Krishnan Mahadevan Corrosion studies of DC reactive magnetron sputtered alumina coating on 304 SS https://doi.org/10.1515/eetech-2017-0001 Received Jun 04, 2017; accepted Sep 14, 2017 Abstract: Aluminum oxide flms on SS 304 deposited by DC reactive magnetron sputtering technique were stud- ied with respect to the composition of the sputter gas (Ar:O 2 ), gas pressure, substrate temperature, current etc. to achieve good insulating flms with high corrosion resis- tance. The flms were characterized by XRD and SEM tech- niques. Potentiodynamic polarization and electrochem- ical impedance spectroscopy measurements were made under static conditions in order to evaluate the corro- sion performance of the alumina-coated SS 304 for vari- ous immersion durations in 0.5 M and 1 M NaCl solution. Alumina-coated SS 304 has low corrosion value of 0.4550 and 1.1090 MPY for 24 h immersion time in both solutions. The impedance plots for the alumina coated SS 304 in 1 M NaCl solution at diferent durations are slightly diferent to when compared to its immersion in 0.5 M NaCl solutions and are composed of two depressed semi circles. For the alumina coated flm, the impedance spectrum decreased, when immersion time increased. Keywords: aluminum oxide; DC reactive sputtering; elec- trochemical corrosion 1 Introduction Amorphous alumina (aluminum oxide) thin flms have many applications and have attracted much attention dur- ing the past 20 years [1]. Aluminum oxide thin flms are widely used in many mechanical, optical and microelec- tronic applications [2]. Due to the mechanical, electrical, thermal and optical properties of aluminum oxide, it has become an important thin flm material for various ap- plications [3] (e.g., protective coatings, difusion barriers, *Corresponding Author: Baskar Thangaraj: Department of Physics (PG), Sourashtra College, Madurai -625004, Tamil Nadu, India; Email: biodieselbaskar@yahoo.co.in Krishnan Mahadevan: Department of Physics (PG), Sourashtra College, Madurai -625004, Tamil Nadu, India electronic seals, dielectric layers and optical layers etc.,) [4]. Aluminum oxide has high melting temperature, hard- ness, abrasion and oxidation resistance, and fnds appli- cation in cutting tools in conjunction with other hard coat- ing materials like TiN, TiCN and TiC [5], it also provides the corrosion resistance of aluminum [6]. The aluminum oxide thin flm can reduce the oxidation rate of superalloys [4]. Due to its high electrical resistivity, alumina coatings are also of interest in the microelectronics industry [5]. This is due to its high electrical breakdown feld, its large band gap and its high dielectric constant [7]. The large band gap of aluminum oxide, for example, facilitates its use in a magnetic tunnel junction, the low thermal conducting, on the other hand makes it a very suitable material for ther- mal barrier coatings as they are used e.g. in gas turbine engines [3]. Complexities in the properties of alumina ex- ist due to the presence of a wide range of diferent crys- talline phases such as α, γ, δ, η, χ, θ and k-alumina [8, 9]. αśAl 2 O 3 can be deposited by chemical vapor deposition (CVD) and physical vapor deposition (PVD) [10]. Gener- ally, the crystalline structure of α, k and θ-Al 2 O 3 is formed by chemical vapor deposition, while η and γ phases are formed by oxidation of aluminum metal, depending on the conditions. Depending on the technique selected and its processing parameters, various options are available for surface modifcations [10]. Chemical vapor deposition is widely used to deposit alumina coatings (usually k-alumina) at 700 - 1000 ∘ C [11]. This process generally ensures good bonding between the substrate and the grown flm, but the thermal expansion mismatch leads to the buildup of residual stress upon cool- ing that adversely afects adhesion though crack gener- ation. These CVD methods also prohibit the coating of high-speed steel (HSS) [12]. Thus the choice of substrate is limited because of high deposition temperature as re- quired for the formation of the stable α-Al 2 O 3 . This draw- back can be minimized by using physical vapor deposition (PVD) operating at lower temperatures. Additionally, PVD techniques ofer the advantage of introducing compressive stresses in the coatings which lead to enhanced fatigue and thermal shock resistance [8]. PVD techniques such as e-beam evaporation, pulsed laser deposition and reactive