Tribocorrosion of 316L stainless steel and TA6V4 alloy in H 2 SO 4 media P. Henry a , J. Takadoum a , P. Berçot b, * a FEMTO-ST, CNRS, Université de Franche-Comté, ENSMM, UTBM ENSMM, 26 Chemin de l’Epitaphe 25030 Besançon Cedex, France b Institut Utinam CNRS UMR 6213, Université de Franche-Comté, 16 route de Gray, 25030 Besançon Cedex, France article info Article history: Received 25 November 2008 Accepted 12 March 2009 Available online 21 March 2009 Keywords: A. Stainless steel A. Titanium alloy B. Tribocorrosion C. Electrochemistry C. Repassivation kinetics abstract Tribocorrosion of stainless steel 316L and titanium alloy TA6V4 has been conducted in a sulphuric acid solution using an apparatus designed and built for evaluating the joint action of corrosion and wear. The material electrochemical and wear behaviours have been investigated during friction tests under electrochemical potential control. The specimens have been submitted to friction against an alumina ball under cathodic, free and anodic potentials. The friction coefficient, the wear rate and the current density were measured and the obtained results were discussed in terms of passivating film stability and repass- ivation kinetics. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Tribocorrosion phenomena involve mechanical and chemical/ electrochemical interactions between surfaces in relative motion in presence of a corrosive environment. The different mechanisms of tribocorrosion are not entirely understood yet, as they involve properties of contacting material surfaces, mechanics of the con- tact and corrosion conditions. During tribocorrosion tests, on one hand, corrosion is accelerated by the rubbing, and on the other hand, wear is accelerated by the corrosion effect [1–6]. The effect of synergy between mechanical wear and chemical corrosion re- sults in a total volume of removed material (V t ) which can in fact exceed the sum of material separately removed by wear and corrosion. The volume V t is given as a function of three components: V t ¼ V w þ V c þ V s ð1Þ where V w and V c are the volume of material removed separately by the effects of wear and corrosion, respectively, and V s represents the synergistic effect between wear and corrosion which can account for 20–70% of the total volume of material [7–12]. Tribocorrosion phenomena are observed in a large number of applications and in many different environments. Some typical examples of such occurrences are included [13] (a) in the moving parts of an engine such as pistons, cylinders and valves with lubri- cants, (b) with eyeglass frames, due to friction with the skin in the presence of perspiration, (c) with electrical connectors (when there is insertion and removal in a humid or corrosive environment), (d) with joint prostheses (when friction occurs in a physiological li- quid), and (e) with components used in plumbing and pump technology. Tribocorrosion is also an important aspect of Chemo-Mechani- cal Polishing processes (CMP) which affects the manufacture of parts for micromechanics as well as silicon wafers for microelec- tronics and nanotechnology. In this work, tribocorrosion phenomena of 316L stainless steel and titanium alloy TA6V4 sliding against an alumina ball in sul- phuric acid H 2 SO 4 0.5 M solution, have been investigated by mea- suring the coefficients of friction, the electrochemical responses and the total metal losses. Results have been discussed taking into account the influence of the electrochemical applied potential, the depassivation/repassivation kinetics of the materials and the amount of material removal. 2. Materials and experimental method The apparatus used in this study has been presented in [14] and is shown on Fig. 1. It consists of a PTFE cell mounted on a ball-on-disc tribometer (called a tribo-electrochemical cell). The ball and specimen holders are both made of PTFE. The metal flats were 316L stainless steel and titanium alloy TA6V4. The ball was polycrystalline alumina with a diameter of 5 mm. The tribocorro- sion tests were conducted at an ambient temperature of 20 ± 1 °C in aerated 0.5 M H 2 SO 4 solution. The tangential force due to fric- tion was measured with a strain gauge during sliding. Informa- tion on the wear processes was obtained by 3D profilometry recordings of the worn surfaces. The motion was linearly recipro- cating at constant speed with a frequency of 1.2, 0.9 or 0.6 Hz, 0010-938X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2009.03.015 * Corresponding author. Tel.: +33 3 81 66 20 30; fax: +33 3 81 66 30 33. E-mail address: patrice.bercot@univ-fcomte.fr (P. Berçot). Corrosion Science 51 (2009) 1308–1314 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci