Wear 259 (2005) 477–481 Short communication Oxide film formation in magnetized sliding steel/steel contact— analysis of the contact stress field and film failure mode K.J. Chin a , H. Zaidi a,∗ , T. Mathia b a Laboratoire LMS (UMR-6610-CNRS), Universit´ e de Poitiers, SP2MI, T´ el´ eport 2, Boulevard Marie et Pierre Curie, BP 30179, 86962 Futuroscope Chasseneuil Cedex, France b Ecole Centrale de Lyon, Laboratoire LTDS, France Received 15 October 2004; received in revised form 14 February 2005; accepted 28 February 2005 Abstract A magnetic field was applied to the sliding contact of ferromagnetic steel/steel on a flat pin/flat disc tribometer, and was found to significantly modify its tribological properties. A thick film of black oxide was formed on the material surface, considerably reducing the friction stress and hence the wear rate. Contact is changed from direct metal/metal to metal/oxide layer/metal. The oxide layer created on the disc undergoes continuous stress which can create damage. Analysis of the stress distribution at the surface and in the sub-surface of the disc shows that there is a high concentration of tensile stress behind the contact zone in the direction of the sliding and that oxide layer rupture occurs in this zone. This is evidenced by cracks appearing in the oxide layer. © 2005 Elsevier B.V. All rights reserved. Keywords: Magnetic field; Oxide layer; Sliding contact 1. Introduction The application of a magnetic field to ferromagnetic steel in sliding contact considerably modifies its tribological be- havior with significant decrease in wear [1–5]. In this study, we focus on the tribological behavior, the formation of the oxide layer and its failure in magnetized contact. We further analyze the surface and subsurface dam- age modes arising from the distribution of the contact stress field. Using methods analogous to SEM analysis and contact stress modeling, the formation and failure of oxide films in sliding contact are also described. ∗ Corresponding author. Tel.: +33 5 49 49 65 00; fax: +33 5 29 29 65 04. E-mail address: hamid.zaidi@lms.univ-poitiers.fr (H. Zaidi). 2. Experimental details The tests were carried under laboratory conditions on a pin-on-disc tribometer (flat pin/flat disc) [1]. Pin and disc were made of ferromagnetic steel AISI 1045. The pin had a cylindrical form with 100 mm in length and 10 mm in diam- eter. The radius of the contact track on disc was 100 mm. In order to reproduce the contact surface in successive tests, the pin was changed and the disc was machined before each ex- periment. Each sliding contact lasted 30 min under different normal load ranging from P = 60 to 240 N at a relative sliding speed of v = 0.38 m/s. A magnetic field was produced using an alternative current applied to a coil located and which de- livered a field intensity variable from H = 0 to 18 kA/m. Oxide film formation in the presence of the magnetic field and its cracking in surface and subsurface were examined by scan- ning electron microscopy (SEM). The wear rate of the pins was deduced from the lost of their mass according to the slid distance in friction. 0043-1648/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2005.02.122