Micro-scratch study of a magnetron-sputtered Zr-based metallic-glass film F.X. Liu a, ⁎, F.Q. Yang b , Y.F. Gao a,c , W.H. Jiang a , Y.F. Guan a , P.D. Rack a,d , O. Sergic e , P.K. Liaw a a Department of Materials Science and Engineering, University of Tennessee, Knoxville, TN 37996, USA b Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506, USA c Computer Science and Mathematics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA d Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA e CSM Instruments Inc., Needham, MA 02494, USA abstract article info Article history: Received 10 November 2008 Accepted in revised form 11 May 2009 Available online 18 May 2009 Keywords: Scratch Metallic-glass film Critical load Coefficient of friction Adhesion Using the micro-scratch technique, the tribological behavior of ZrCuAlNi metallic-glass films on 316L stainless steel was studied. With the application of ramping load, the critical load of about 110 mN was determined, at which the coefficient of friction increased sharply and the indenter penetration depth reached the film thickness. No clear evidence of film debonding was found, which, together with the observation of multiple shear bands, indicated good adhesion and ductility of the metallic-glass film. When subjected to constant loads, the coefficient of friction increased rapidly once the critical load was passed. The scratch results and the scanning-electron microscopy observations demonstrated good adhesion between the film and the substrate, which may be due to the good interfacial bonding and low residual stress in the film. © 2009 Elsevier B.V. All rights reserved. 1. Introduction Metallic glasses are promising structural materials due to their unique physical and mechanical properties. However, the application of bulk-metallic glasses (BMGs) is hindered by their brittleness and low ductility [1–4]. It has recently been found that the mechanical properties, especially the ductility of some Zr-based metallic glasses, in the form of thin plates and films, can be enhanced due to the effect of geometrical confinement [5–7]. Thus, Zr-based metallic-glass films have recently attracted much interest because of their good mechan- ical, tribological, and/or corrosion properties [4,8–12]. Potential applications of metallic-glass films have been studied as nano-scale patterning materials and the materials for microelectromechanical systems and devices [8,9]. Enhanced fatigue properties of crystalline substrates from some Zr-based metallic-glass films have been observed [10,11]. To improve the surface performance of multilayer structures, good mechanical and tribological behaviors of surface films are desired [11]. Because of the thickness confinement in surface films, suitable methods need to be utilized to probe these behaviors. For example, the nanoindentation technique has been extensively used in studying mechanical behavior of surface films. By continuously recording the variation of the penetration depth with the indentation load, nanoindentation can be effectively used in studying the mechanical behavior of surface films, such as hardness, elastic modulus, residual stress, and interfacial fracture toughness [13–15]. On the other hand, scratch test is widely used to investigate the tribological behavior of surface films. In a scratch test, an indenter tip is scratching over the surface of the film to generate a groove under constant or incremental normal loads. The tangential force is measured during the test, and the morphology of the scratches can be observed simultaneously or afterwards. At a certain load, the coefficient of friction (i.e., COF, the ratio of the tangential force to the normal force) and the slope of the penetration depth might exhibit an abrupt change, which corresponds to the initial adhesion failure of the film. And this load is defined as the critical load. By analyzing the material deformation and material removal during scratch testing with respect to the loading conditions, the friction and wear behavior of the films can be studied [16,17]. In this work, the tribological behavior of the as-sputtered Zr-based metallic-glass films over a 316L stainless steel was examined by a micro-scratch tester. The variation of the frictional force under both ramping loads and constant loads was recorded and correlated with the deformation behavior of the film/substrate system. The deforma- tion behavior of the film was examined with scanning electron microscopy (SEM). The adhesion behavior of the film was discussed based on the friction force measurements and SEM observations. 2. Experimental procedures An AJA ATC2000 radio-frequency magnetron-sputtering system (AJA International, INC, North Scituate, MA) was used to deposit a Zr- based metallic-glass film over a well cleaned 316L stainless steel of 20% cold work. Rectangular steel bars with a dimension of 3×3×25mm 3 were ground with 1200-grit sandpapers, and polished mechanically to ensure a smooth surface. The sputtering target was a Surface & Coatings Technology 203 (2009) 3480–3484 ⁎ Corresponding author. Tel.: +1 865 974 0645. E-mail address: fliu5@utk.edu (F.X. Liu). 0257-8972/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2009.05.017 Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat