Surface and Coatings Technology 180 –181 (2004) 49–52 0257-8972/04/$ - see front matter  2003 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2003.10.034 Effect of substrate surface ion bombardment etching on reaction between chromium thin films and steel substrates R. Gheriani *, R. Halimi , R. Bensaha a, b b Physical Laboratory of Materials, University of Ouargla, Ouargla 30.000, Algeria a Unity of Research, Materials and Applications, University of Constantine, Constantine 25.000, Algeria b Abstract Thin coating films of transition metal carbides and nitrides are used because of their refractory characteristics and good mechanical properties. In this work we study the interaction between chromium thin films and steel substrates 100C6 type (AFNOR norms) containing approximately 1 wt.% of carbon. Chromium films are deposited at 200 8C by magnetron sputtering. In order to study the correlation between the pre-cleaning of substrates and the properties of coatings, two series of samples were prepared; the first is distinguished from the second by ion bombardment etching before chromium deposition. The study is carried out by X-ray diffraction, Auger electron spectroscopy, scanning electron microscopy and Vickers micro-hardness measurements. The changes observed in sample characteristics after heat treatments are associated with carbon and iron diffusion and with carbide formation. It is established that the micro-hardness of the first series is higher than that of the second series. This large difference is due to substrate etching, as induced by surface ion bombardment.  2003 Elsevier B.V. All rights reserved. Keywords: Chromium; Thin films; Carbides; Etching 1. Introduction Thin films of transition metal carbides and nitrides, obtained by different techniques like chemical and phys- ical vapour deposition (CVD and PVD), are extensively used in many applications owing to their properties, such as high melting point, high hardness, excellent wear resistance, high oxidation resistance and low fric- tion coefficient w1–5x. These coating films can consid- erably improve the characteristics of surface layers of materials, particularly the adhesion to the substrates. Indeed, several parameters influence the adhesion, including stresses in the film, contamination at the interface, chemical bonding between the thin film and the substrate, pre-cleaning of the substrate surface, etc. Ion bombardment etching appears to be one of the most effective methods in PVD processing to improve the adhesion of thin films w6x. In this work we study the influence of substrate cleaning by ion bombardment etching on reaction and adhesion of chromium thin films with steel substrates. We prepared two series of samples; *Corresponding author. Tel.: q213-29-71-2627; fax: q213-29-76- 5577. E-mail address: ragheriani@yahoo.fr (R. Gheriani). in the first series, the substrates are cleaned by argon ion bombardment before chromium deposition. The formation and growth of different compounds between substrates and chromium films after various heat treat- ments are investigated by X-ray diffraction (XRD), Auger electron spectroscopy (AES) and scanning elec- tron microscopy (SEM). 2. Experimental 2.1. Preparation of samples Steel substrates (100C6 type) were mechanically polished and ultrasonically cleaned with trichloroethyl- ene, acetone and methanol successively for 10 min each. Two series were prepared. The first one was subjected to an additional ion bombardment cleaning for 10 min just before Cr deposition. Pure chromium (99.99%) thin films were deposited under vacuum (;10 mbar) by y4 magnetron sputtering with RF power 200 W and sub- strate temperature 200 8C, during 1 h of deposition. Film thickness (3000 A) is measured by talystep and ˚ Rutherford backscattering spectrometry. The samples are subjected to high vacuum annealing at a temperature between 450 and 700 8C for 30 and 60 min.