Electrochimica Acta 49 (2004) 3057–3065 Influence of chromium and cerium implantation in the electrochemical development of passive layers on AISI 304L C.M. Abreu, M.J. Cristóbal ∗ , X.R. Nóvoa, G. Pena, M.C. Pérez, C. Serra Universidade de Vigo, E.T.S.E.I., Lagoas-Marcosende, 9 E-36200 Vigo, Spain Received 9 May 2003; accepted 6 January 2004 Available online 26 April 2004 Abstract In this work X-ray photoelectron spectroscopy studies and electrochemical techniques are combined to elucidate the effect of Ce and Cr implantation in the formation and evolution of passive layers generated by potentiodyinamic cycling on AISI 304L steel in alkaline medium. Cerium implantation promotes the formation of a thinner and more protective film on the steel. This fact, noticed in X-ray photoelectron spectroscopy (XPS) analysis, is reflected in the voltammograms by an important decrease of the magnetite formation and Cr 3+ /Cr 6+ oxidation peak and, in the electrochemical impedance spectroscopy (EIS) diagrams, as the disappearance of one time constant. Chromium implantation contributes also to the generation of a thinner film, but more defective than in the case of cerium implantation. These differences are demonstrated in both electrochemical and surface analytical techniques. In the voltammetric curves, the diminution of the iron oxides signal is less notorious and an important increasing in the Cr 3+ /Cr 6+ oxidation peak is registered. The EIS results show the persistence of the same number of time constants detected in the unimplanted steel. © 2004 Elsevier Ltd. All rights reserved. Keywords: Ion implantation; AISI 304L; Cyclic voltammetry; EIS; XPS 1. Introduction Ion implantation re-alloys the surface of tool steels con- ferring the characteristic special properties. This is achieved by means of an ion accelerator, which ‘shoots’ ions into the tool’s surface at very high speed. The ions penetrate the sur- face and re-alloy it. This increases the resistance of the sur- face to wear, friction, adhesion and corrosion [1]. Thus, ion implantation is not a coating, which means that there is no risk of delamination and that surface finishing is not changed by the treatment. Furthermore, no change of dimensions and shape will take place since ion implantation is carried out at low temperatures, typically below 180 ◦ C. In short, the treatment involves no risks, and if later refurbishment is required, ion implantation will not be an impediment. The increasing severity of environmental protection reg- ulations has promoted a great number of investigations oriented to reduce the use of chromium in the industry ∗ Corresponding author. Fax: +349-86-812201. E-mail address: mortega@uvigo.es (M.J. Crist´ obal). of metallic protection. In this context, ion implantation technique has proved to be a good alternative, allowing a better control on the quantity of used elements. During the last years several works have been reported concerning the chromium implantation on different alloys [2,3]. The use of chromium ion implantation is a great step forward for many manufacturers of plastic products. Injection moulds exposed to corrosive gases (from the plastics) can improve their ser- vice life by 3–10 times by chromium ion implanting, and the need of tool refurbishment is reduced markedly. This means that unintended and expensive production standstills can be avoided. The treatment is applied only on the sur- faces exposed to attack, which shorts the treatment time and, consequently, the cost that results relatively low. At the same time, the use of substitutive reactive elements such as yttrium, cerium and other rare earths, that have proved to be very effective in the treatment of materials for high temperature oxidation [4–6] has been proposed for low temperature wet corrosion. Several mechanisms have been proposed for understanding this effect of rare earth metals. Most of those studies attribute the oxidation rate decreasing to a change in the transport process for scale growth. 0013-4686/$ – see front matter © 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2004.01.065