Corrosion properties of N-doped austenitic stainless steel films prepared by IBAD Yo-Seung Song a , Joon-Hee Lee a , Ku-Hyun Lee b , Deuk Yong Lee c,d, * a Department of Materials Engineering, Hankuk Aviation University, Koyang 412-791, South Korea b Surface Engineering Department, Korea Institute of Machinery and Materials, Changwon 641-010, South Korea c Department of Materials Engineering, Daelim College of Technology, Anyang 431-715, South Korea d Department of Mechanical Engineering, University of Nevada, Reno, NV 89557, USA Received 9 February 2004; accepted in revised form 15 June 2004 Available online 7 August 2004 Abstract Nitrogen incorporation into 316-L stainless steel was performed by ion beam assisted deposition (IBAD) equipped with one Kaufman ion beam source in Ar/N 2 gas mixture and one electron beam source to investigate the effects of Ar/N 2 gas ratio on the crystal structure and corrosion resistance of the coatings. An austenitic fcc structure with strong (111) preferred orientation was found for the 316-L films grown under ion bombardment. Corrosion resistance of the N-doped 316-L films were superior or equivalent to the bulk 316-L steel, respectively, when they are tested in 3.5 wt.% NaCl or 0.1 M H 2 SO 4 solutions. Salt spray test results revealed that the corrosion resistance of S45C mild carbon steel was improved significantly by 160% when the N-doped austenitic stainless steel films were deposited, suggesting that the N- doped austenite films are beneficial to anticorrosion properties. D 2004 Elsevier B.V. All rights reserved. Keywords: Ion beam assisted deposition (IBAD); N-doped austenitic stainless steel film; Polarization curve; Salt spray test; Corrosion 1. Introduction Although austenitic stainless steels are resistant to the wide range of environmental atmosphere due to their corrosion and oxidation resistant properties, resulting in extensive use in structural and chemical industries, they possess inferior wear properties [1–3]. Nowadays, surface- hardening treatments using magnetron sputtering, arc discharge deposition and ion beam assisted deposition (IBAD) are introduced to solve wear problems of stainless steels. Sikola et al. [4] reported that metal nitrides prepared by IBAD showed excellent physical, chemical and mechan- ical properties. Also, IBAD has advantages of controlling deposition parameters such as atom flux, ion energy and ion incidence angle independently. The thermodynamically stable form of the coated stain- less steel at room temperature is a ferritic bcc structure, which has a relatively lower corrosion resistance. Ferritic stainless steel coatings can be prevented by using high substrate temperature above 500 8C or by epitaxial growth on the austenite substrate [5–8]. However, these solutions lead to a limitation of the potential choice of substrate materials for the coatings [8]. Nitrogen-doped austenitic stainless steel exhibiting higher surface hardness was synthesized by magnetron sputtering under Ar/N 2 gas mixture atmosphere while maintaining reasonably high corrosion resistance [8,9]. Although the nitrogen-doped coatings exist in the form of a metastable supersaturated fcc structure, the structure is likely to change depending on the substrate temperature and nitrogen concentration. In the present study, the austenitic 316-L stainless steel films are synthesized on the glass by IBAD due to the ease of controlling the deposition parameters. The IBAD apparatus was composed of one heat resistance for thermal evaporation (TE) and one Kaufman ion beam source. In the TE process, 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.06.024 * Corresponding author. Active Materials and Processing Laboratory, Department of Mechanical Engineering, University of Nevada-Reno, Reno, NV 89557, USA. Tel.: +1 775 784 7782; fax: +1 775 784 1701. E-mail address: dylee@daelim.ac.kr (D.Y. Lee). Surface & Coatings Technology 195 (2005) 227– 233 www.elsevier.com/locate/surfcoat