Electrochimica Acta 107 (2013) 238–247 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom ep age: www.elsevier.com/locate/elec tacta On the electrochemical behavior of Cu–16%Zn–6.5%Al alloy containing the   -phase (martensite) in borate buffer M. Blanco a , J.T.C. Barragan a , N. Barelli a , R.D. Noce a , C.S. Fugivara a , J. Fernández b , A.V. Benedetti a,∗ a Departamento de Físico-Química, Instituto de Química, Univ. Estadual Paulista, UNESP, 14801-970 Araraquara, SP, Brazil b Departamento de Ciencia de Materiales e Ingeniería Metalúrgica, Universitat de Barcelona, 08028 Barcelona, Spain a r t i c l e i n f o Article history: Received 7 January 2013 Received in revised form 27 April 2013 Accepted 26 May 2013 Available online 18 June 2013 Keywords: Cu–Zn–Al alloys Martensite Borate buffer Cyclic voltammetry a b s t r a c t In this work, the electrochemical behavior of Cu–16(wt.%)Zn–6.5(wt.%)Al alloy containing the   -phase (martensite) was studied in borate buffer solution (pH 8.4) by means of open-circuit potential (E OC ), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The alloy E OC was −0.29 V vs. Hg/HgO/OH − , similar to that of pure copper in this medium, indicating that the processes which occur on the alloy surface are mainly governed by copper. EIS response was related to the dielectric and transmission properties of the complex oxide layer. The CVs showed peaks concerning the redox reactions for copper and zinc. These peaks were assigned to the formation and reduction of copper and zinc species. Furthermore, they showed that the copper oxidation was suppressed by the presence of zinc and aluminum in the alloy composition. The copper and zinc oxidation to form complex oxide layers and the reduction of the different metallic oxides generated in the anodic potential scan suggest that a solid state reaction could determine the metallic oxide formation. © 2013 Elsevier Ltd. All rights reserved. 1. Introduction The so-called shape memory effect in copper-based alloys is intrinsically related with the martensitic transformation which occurs from the austenite phase () to the martensite (  ) [1,2]. Many alloys undergo this transformation and then exhibit shape memory effect such as Ni–Ti, Au–Cd, Cu–Zn, Cu–Al, Cu–Zn–Al, Cu–Al–Ni and Cu–Al–Mn [3–5]. In this sense, Ni–Ti alloys have demonstrated to be a better material for most technological appli- cations; however, Cu–Zn–Al ones are a cost-effective alternative [6]. In addition, it worth mentioning that Cu-based alloys may present a large temperature range in which the shape memory effect can be modulated depending on their chemical composition [7–11]. Specifically, in Cu–Zn–Al alloys, the shape memory effect is only observed for a certain range of composition which in general contain Cu–(16–30)Zn–(4–8)Al (wt.%). With respect to this com- positional range, three equilibrium phases (,  and ) may occur as well as their respective martensitic ones, typically denoted as   ,   and   [10,12,13]. It is difficult to take place the martensitic transformation for Cu-Zn-Al alloys containing  or  phases and ∗ Corresponding author. Tel.: +55 1633019652; fax: +55 16 3322 7932. E-mail addresses: benedeti@iq.unesp.br, avbenedetti@gmail.com (A.V. Benedetti). therefore for a practical viewpoint, the only phase that presents the shape memory effect is the  one. The -phase in Cu–Zn–Al alloys is disordered at high temperatures and has a bcc lattice. During the cooling process, the parent -phase may give rise to two different superlattice structures, depending on the temperature and alloy composition, by means of an ordering reaction. These structures are normally designated as  2 (B2) and  3 (L2 1 ) [1]. By stress-induced or thermally, the  2 or  3 austenite phases transform into the   one (martensite) which is also known as 9R due to the rhombohedral lattice and stacking of 9 compact plans. It is well known the corrosion behavior of Cu–Zn alloys in the presence of chloride ions, mainly the effect of zinc content in the dezincification (process in which the zinc is leached out), which is more pronounced in the zinc-rich phase. Therefore, the dezincifica- tion on brass follows the order: -phase > - + -phase > -phase. The effect of the Al addition on the dezincification of aluminum brasses was studied [14] and it was concluded that the addition of Al (up to 2 wt.%; Al is commonly used in condenser tubes) decreases the dezincification of these ternary alloys when compared to brass alloys only. A comparative study of the dezincification behavior of austenite () and martensitic (  ) Cu–Zn–Al alloys in differ- ent conditions (sample immersion in a 10 g/L CuCl 2 solution at 20 ◦ C for 24 h using 250 mL solution/cm 2 ; sample immersion for 14 days at 20 ◦ C into a solution containing 13.5 g/L FeCl 3 ·nH 2 O, 18.7 g/L CuSO 4 ·5H 2 O and 1.5 mL/L HCl, and weight loss in running tap water) was reported by Celis et al. [15]. They observed that 0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2013.05.147