Long term performance of atomic layer deposition coatings for corrosion protection of stainless steel E. Marin*, A. Lanzutti, L. Paussa, L. Guzman and L. Fedrizzi The use of atomic layer deposition (ALD) for the corrosion protection of metallic substrates was speculated for the irst time in the 1990 s. Since then, a lot of research has been carried on to investigate the application limits of this technique. ALD has been ef iciently used to deposit conformal oxide layers on different metallic substrates, which were used as insulators and diffusion barriers to prevent contact between aggressive electrolytes and metal. In this work, a complete morphological and compositional characterization of some ALD coatings has been carried out using atomic force microscopy and glow discharge optical emission spectrometry. Electrochemical impedance spectroscopy and potentiodynamic polarizations have been used to evaluate the over-time performance of three different ALD deposits on AISI 316 stainless steel, namely TiO 2 , Al 2 O 3 and AlN, and the results have been compared to previous literature data. It has been observed that, in contrast with the previous literature results, Al 2 O 3 layers deposited on AISI 316 do not suffer premature failure. On the contrary, a lower and time-dependent corrosion protection was observed when using TiO 2 coatings and a decrease of corrosion protection over time due to oxidative phenomena of the protective layer has been observed in the case of the AlN coatings. 1 Introduction In the ield of engineering, when a balanced combination of corrosion resistance and mechanical performances is requested, austenitic stainless steels of the AISI 300 series, such as AISI 304 and AISI 316, are often the best candidates. Thanks to their high chromium and nickel contents, austenitic stainless steel are corrosion resistant in a wide range of industrial and domestic applications, such as pressure vessels, cutlery, turbine blades, civil structures and biomedical components. From a composi- tional point of view, the only difference between 304 and 316 is the latter containing molybdenum, which further improves pitting and crevice corrosion resistance, in particular in presence of high amounts of chlorides. For this reason, 316 has been widely applied also for naval components. The presence of a spontaneously formed, conformal chromium oxide layer on the surface of austenitic stainless steel is not only protective against corrosion, but also an effective diffusion barrier that prevents diffusion of potentially dangerous or toxic elements, such as nickel. For this reason, 316 and, in particular 316 low carbon (L) has been widely applied in aggressive biological environments for high performance prosthetic implants [1–5]. Additional uses of AISI 316 L also include high temperature applications thanks to its natural immunity to sensitization [6–10]. Even if AISI 316 L is characterized by a balanced combination of mechanical properties and corrosion resistance, less mechanically performing titanium alloys such as Ti-6Al-4V are still preferentially used in biomedical components because of their superior corrosion resistance, in particular for not highly stressed parts. A great number of innovative treatments are nowadays under intensive study to further improve stainless steel corrosion resistance, such as plasma detonation techniques [11], arc-ion plating [12], sol-gel deposition [13,14], chemical conversion layers of cerium [15], chromium [16] or other elements, chemical vapor deposition (CVD) [17], high-velocity oxy-fuel spray [18], plasma- nitriding [19], and lately atomic layer deposition (ALD) [20–25]. Using ALD, a wide array of materials can be deposited, including chemical compounds, metal oxides, nitrides, sulides, carbides, luorides, pure metals, biomaterials and even polymers [26,27]. The main advantages of ALD technologies when compared to CVD and PVD are the higher process control and the possibility to deposit more conformal layers even on complex 3 d shaped substrates. It has been observed in literature that ALD is one of the few techniques that can conformally coat the inner surface of nanotubes with high form factors [28,29]. As conventional CVD, ALD practical industrial applications on metals are in reality strongly limited due to the required process temperature. If the chamber temperature exceeds the E. Marin, A. Lanzutti, L. Paussa, L. Guzman, L. Fedrizzi University of Udine, via Cotonificio 108, Udine 33100, (Italy) E-mail: elia.marin@uniud.it Materials and Corrosion 2015, XXX, No. XXX DOI: 10.1002/maco.201408012 1 www.matcorr.com wileyonlinelibrary.com © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim