Wear 266 (2009) 832–838 Contents lists available at ScienceDirect Wear j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / w e a r Duplex SiCN/DLC coating as a solution to improve fretting—Corrosion resistance of steel David Pech a , Norbert Schupp b , Philippe Steyer a,∗ , Theo Hack b , Yves Gachon c , Christophe Héau c , Anne-Sophie Loir d , Juan Carlos Sánchez-López d a Laboratoire MATEIS, INSA-Lyon, Bât. Blaise Pascal, 69621 Villeurbanne Cedex, France b EADS Deutschland GmbH - Innovation Works, D-81663 München, Germany c HEF R&D SAS, ZI Sud, Rue Benoît Fourneyron, 42166 Andrézieux-Bouthéon Cedex, France d Instituto de Ciencia de Materiales de Sevilla, CSIC-US, Avda. Américo Vespucio 49, 41092 Sevilla, Spain a r t i c l e i n f o Article history: Received 18 December 2007 Received in revised form 15 October 2008 Accepted 1 December 2008 Available online 7 December 2008 Keywords: PACVD SiCN DLC Fretting corrosion a b s t r a c t Fretting corrosion damages are commonly observed when two metallic bodies, which are in contact with each other, are subjected to oscillatory motions of low amplitude. Such kind of degradation mode is often responsible for limited durability of aeronautical joints. In the present paper,a multifunctional duplex coating based on Si–C–N and diamond-like carbon (DLC) materials, combining corrosion resistance and good tribological properties is described. Amorphous hydrogenated SiC, SiCN, SiC/DLC and SiCN/DLC were deposited on steel substrates by a plasma assisted chemical vapour deposition (PACVD) technique, using tetramethylsilane (TMS), ammonia (NH 3 ) or acetylene (C 2 H 2 ) as gas precursors. Nitrogen incorporation has shown to improve the corrosion protection ability of SiC coatings. The corrosion behaviour and the tribological performance in aqueous media of SiCN/DLC coating have therefore been investigated. A test rig has been designed to validate the fretting resistance of this duplex coating for aeronautic applications. It was found that the combination of a SiCN-based PACVD sublayer with a DLC topcoat could provide an enhanced solution to withstand both fretting and corrosion. © 2008 Elsevier B.V. All rights reserved. 1. Introduction Fretting is the predominant wear phenomena in the field of aero- nautics [1–3]. It can occur on different parts like bolts, axis and bearings where different metallic components are in contact and undergo a repeated relative surface motion, as induced for example by vibrations. Mechanical components with relative micromove- ments (in the scale of nm up to 100 ␮m) suffer from fretting. The characteristic of fretting of steel components is the formation of black iron oxide Fe 3 O 4 which is transformed into red/brown ␣- Fe 2 O 3 in the presence of oxygen and water vapour. So air humidity is an important parameter for fretting of metals and ceramics [4]. Aggressive environment can favour fretting.The fretting process can lead to other wear damages like abrasive wear due to the cor- rosion products, adhesive wear and fatigue. Thus, materials need to have the desired corrosion, friction and wear properties. The use of lubricants is considered as one of the possible solu- tions for preventing fretting corrosion. Liquid lubricants reduce the mechanical wear by placing an intermediate lubricating film between both surfaces, which slows down the oxidation process, ∗ Corresponding author. Tel.: +33 4 72 43 81 69; fax: +33 4 72 43 87 15. E-mail address: philippe.steyer@insa-lyon.fr (P. Steyer). and minimizes corrosion owing to some added inhibitive species [5]. Nevertheless, surface defects cannot be avoided with standard lubricants, and the extent of damage can only be limited. Other mitigating methods are surface modification technique and inter- facial layers [6]. The most common solid lubricant in industrial tribology is molybdenum disulfide [7,8]. However, its efficiency depends on a lot of parameters, and its application is usually lim- ited by its expensiveness.In the case of ceramic coatings,where coating material is harder than the substrate, the wear resis- tance against fretting wear is improved [9,10]. Diamond-like carbon (DLC) coatings are well known as low-friction coatings.Applying such coatings to components that are exposed to fretting dam- age has been investigated in the past to improve the behaviour in comparison with conventional uncoated systems [11,12]. Unfortu- nately,DLC coatings are better known for their intrinsic lubricant characteristics rather than for their anti-corrosion performance [13–15]. The adherence of DLC films is improved with an amor- phous SiC underlayer [16].Si-based coatings deposited by PACVD have shown good anti-corrosion properties.The films are gener- ally dense and amorphous, and their electrical insulating properties explain their outstanding performance in terms of corrosion pro- tection [17–19]. A multi-layered structure could therefore enhance the corrosion protection effect while providing a good tribologi- cal behaviour.The aim of this work is to characterise and explain 0043-1648/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2008.12.007