Electrochemical and XPS studies of sputter-deposited ternary Mn / Ta  /Cr alloys in chloride-free and chloride-containing sulphuric acid solutions Ahmed A. El-Moneim b , Khaled M. Ismail a , Waheed A. Badawy a, * a Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt b Physical Chemistry Department, National Research Center, Giza, Egypt Received 28 August 2001; received in revised form 1 February 2002 Abstract Amorphous manganese-rich (67  /80 at.%) Mn  /Ta /Cr alloy films were prepared by DC magnetron sputtering method. The corrosion behavior and stability of the Mn  /Ta /Cr alloy films were examined in chloride-free and -containing 1 M H 2 SO 4 . AC and DC electrochemical techniques in combination with XPS analysis were used. Mn /Ta  /Cr alloys exhibited very high corrosion resistance and stability up to transpassive dissolution region of chromium. The high corrosion resistance of Mn  /Ta  /Cr sputtered films is based on the formation of double oxyhydroxide passive film composed mainly of chromium and tantalum. The partial substitution of tantalum with chromium improves the corrosion resistance of the sputter-deposited alloys via accelerating the preferential dissolution of manganese and stabilizing alloy/passive film interface. A change in the passive film structure was observed when the alloys were anodically polarized at potentials higher than 0.6 V (SCE). # 2002 Elsevier Science Ltd. All rights reserved. Keywords: XPS; Mn /Cr  /Ta; Ternary alloys; H 2 SO 4 ; EIS; Chloride ions 1. Introduction Sputter-deposited alloy films have been reported to exhibit remarkable intrinsic corrosion resistance. Using sputter-deposition, single-phase alloys can be produced under non-equilibrium condition and the concentration of corrosion resistant alloying elements may exceed their thermodynamic solubility limit. As with most corrosion- resistant engineering alloys, sputter-deposited alloy films owe their corrosion resistance to the presence of a protective passive film. It has been found that the corrosion rates of the sputtered chromium-valve metal alloys are several orders of magnitude lower than those of their constituent elements [1  /5]. The high corrosion resistance was attributed to the particular composition of the passive films and/or the synergistic interaction between the cations of alloy components in the passive films. It has been also reported that the addition of a third element to the binary alloys rich in a reactive metal is an effective mean for extending the amorphization range as well as improving the corrosion resistance. For example, the addition of molybdenum to Al  /Ti and Al / Cr alloys improves their corrosion resistance [6  /8]. The beneficial role of a third element addition has been classified into two groups: (i) acceleration of the cathodic activities in the passive region of the passivat- ing elements; (ii) the formation of a stable passive film due to synergistic interaction of passivating cations. In an attempt to improve the corrosion resistance of a reactive metal like manganese, the effect of tantalum content on the stability of sputter-deposited amorphous Mn  /Ta alloys in chloride-free and -containing sulfuric acid solutions was investigated [4,9]. It has been found that the corrosion rate decreases exponentially with the tantalum contents, and that the corrosion behavior of the binary alloy is dependent on its composition. At 40 at.% Ta or above, no considerable corrosion or pitting attack was recorded, while at 5/30 at.% Ta, significant corrosion rate was recorded [4,9]. * Corresponding author. Tel.:  /20-2-5676558; fax:  /20-2-5727556. E-mail addresses: wbadawy50@hotmail.com (W.A. Badawy), wbadawy@main-scc.cairo.eun.eg (W.A. Badawy). Electrochimica Acta 47 (2002) 2463  /2472 www.elsevier.com/locate/electacta 0013-4686/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII:S0013-4686(02)00106-8