Surface modification of austenitic stainless steel on the surface of electric contact during low frequency current circulation L. Nachez a, ⁎ , B.J. Gómez a , J. Ferrón a , J. Feugeas b a Instituto de Física Rosario (CONICET-UNR), Bvrd. 27 de Febrero 210 Bis., 2000 Rosario, Argentina b Instituto de Desarrollo Tecnológico para la Industria Química (CONICET-UNL), Güemes 3450, 3000 Santa Fe, Argentina Received 20 July 2005; received in revised form 30 November 2005; accepted 7 February 2006 Available online 24 March 2006 Abstract During process of surface treatment of steels using plasmas (ion nitriding, physical vapor deposition and chemical vapor deposition, plasma immersion ion implantation, etc.), normally, one of the surfaces of the pieces has to be in electrical contact with one of the electrodes. In this work, we investigate the surface modification of the SAE EV12 stainless steel after being in electrical contact with the cathode during a normal process of ion nitriding. The physical conditions used were of a square wave electrical current of 10, 100 and 1000 Hz with an amplitude between 40 A m -2 and 80 A m -2 passing during 40 min. The treated surface was studied under Auger emission spectroscopy and grazing angle X-ray diffraction. The results have shown that a surface layer of 60 nm is strongly altered, and that the results depend on the frequency of the applied voltage and the pressure of contact between the surface and the cathode. In this surface layer, we could see the Fe–Cr, MnO and a carbide of the type (Fe,Ni) 23 C 6 called haxonite, only reported in meteorites. © 2006 Elsevier B.V. All rights reserved. Keywords: Electromigration; Steel; Diffusion; Surface and interface states; Depth profiling 1. Introduction It is known that a current circulation through the surface of steels produces modifications. This electric current surface modification is originated in the thermal effect caused by the Joule effect of the current. Normally, the current on the steel is induced by a high frequency alternating magnetic field induced by the also high frequency alternating external current. This heating happens on the surface of the material in a process that is known as skin effect. On the other hand, on magnetic steels, another heating effect can occur and it is originated in the hysteresis cycle loses due to the movements of the magnetic domains of the material. Nevertheless, this effect only occurs at temperatures below the Curie temperature of the material, which on steels depend on the carbon content. But this steel modification originated in electric currents and magnetic flux at the end originated in a heating process [1]. During the surface treatment of steels with plasmas, like chemical vapor deposition (CVD) and physical vapor deposition (PVD), plasma immersion ion implantation (PIII), ion nitriding, etc. [2,3], the samples to be treated have to be electrically connected to ground potential [4,5]. Normally (like in the ion nitriding, which is the particular case of this work) [6,7], the samples are electrically connected by gravity through one of the surfaces. This surface can suffer the effect of the pass of the current during an amount of time that can vary between tens of minutes to several hours, with an increase of the temperature up to 400 °C–600 °C. Depending on the system, the applied voltage can be, always thinking in the ion nitriding process, between 350 V and 700 V, DC or square wave modulated voltage with frequencies between 10 Hz and several hundreds kHz, with the active/passive ratio variable. The resulting current that circulates, and that will depend on the process and the electric parameters of the external circuit, results between 30 and 100 A m -2 [8]. On the other hand, in industrial applications, the piece to be treated sometimes has to be ion nitrided in all of his faces, implying that even Thin Solid Films 513 (2006) 206 – 211 www.elsevier.com/locate/tsf ⁎ Corresponding author. E-mail address: nachez@ifir.edu.ar (L. Nachez). 0040-6090/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2006.02.012