Preparation, corrosion and structural properties of Cu–Ni multilayers from sulphate/citrate bath N. Rajasekaran, S. Mohan * Central Electrochemical Research Institute, Karaikudi 630 006, India article info Article history: Received 11 November 2008 Accepted 29 May 2009 Available online 11 June 2009 Keywords: A. Metal coatings (TM) B. Potentiostatic (T) B. EIS (T) C. Electrodeposited films (PP) abstract Potentiostatic electrodeposition was used to produce Cu–Ni multilayer by two-wave pulse plating tech- nique from sulphate/citrate electrolyte at pH 4. Cyclic voltammetry studies provide information about the deposition potential. The compositions of multilayers were studied using X-ray fluorescence (XRF). Electrochemical corrosion studies of the deposited multilayer on copper were studied by potentiodynam- ic polarization and electrochemical impedance spectroscopy (EIS). The surface of the layer having smooth, small grain and compact structure was confirmed by scanning electron microscopy (SEM) and atomic force microscopy (AFM) analysis. The face centered cubic lattices are present in the Ni–Cu multi- layer and this is confirmed by the X-ray diffraction (XRD) data. The multilayer structures have better cor- rosion resistance than the base substrate. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction There has recently been a growing interest in electrodeposited multilayer [1], especially since it has been demonstrated [2,3] that they can exhibit a significant giant magnetoresistance (GMR) ef- fect. Therefore, Cu–Ni multilayer obtained by pulse electrodeposit- ion methods has been studied. The properties of the multilayer deposits are significantly affected by parameters such as the elec- trolyte concentration, pH, and the deposition potential, additive, substrates and the control methods (potentiostatic and galvano- static). The effect of these parameters has been studied extensively [4,5–13]. A complexing agent is required for the deposition of Cu– Ni multilayer; cyanide [14], citrate [15,16], pyrophosphate [17], and glycine [18] were studied as the complexing agent. The sul- phate/citrate electrolyte can produce Cu–Ni multilayer of high structural quality [19]. In this perspective, the present work aims to study the forma- tion of Cu–Ni multilayers from the sulphate/citrate electrolyte by two-wave pulse plating technique and evaluates their characteris- tic properties. The tri-sodium citrate was chosen as the complexing agent due to its ability to improve the deposition efficiency, to ob- tain stress free deposits and its relatively less toxic nature [15]. 2. Experimental Cu–Ni multilayers were deposited on Cu foil substrate. The Cu foil substrate was mechanically polished and degreased with acetone in order to remove the impurities. The substrate surface was than electrochemically cleaned with alkali solution and chemically treated for few seconds in 10% H 2 SO 4 . Pulse electro- deposition of the Cu–Ni multilayer was carried out using the electrolyte that contains CuSO 4 , NiSO 4 and tri-sodium citrate. Deionized water was used to prepare the electrolyte solution. The deposition was carried out in a three-electrode cell system under potentiostatic control using Parstat 2273 model electro- chemical analyzer. A platinum sheet was used as a counter elec- trode (anode). The cathode (Cu foil substrate) potentials are referred to a saturated calomel electrode (SCE). Deposition of Cu layer was carried out at the cathode potential 0.4 V (vs SCE), while the deposition of Ni layer was 1.19 V (vs SCE) and pH 4. The corrosion behavior of the multilayer was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) using Parstat 2273 Princeton advanced elec- trochemical system. The structure of the multilayer was studied using X-ray diffractometer. The surface morphology of the deposited multilayers was examined with SEM and AFM. 3. Result and discussion The Cu–Ni multilayer deposits from the sulphate/citrate bath was adherent smooth and bright in appearance. The compositions of the deposits were measured by using X-ray fluorescence, these results shows that the percentage of Cu in the deposit is 62% and Ni is 38%. The multilayer deposits samples were bent through 180° angle and deposit shows no lifting and peeling, which shows good adhesion of these coatings on the copper substrates. Deposits with a Vickers hardness of 291 HV (25 g) were obtained. 0010-938X/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2009.05.052 * Corresponding author. Tel.: +91 4565 227551; fax: +91 4565 227713. E-mail address: sanjnamohan@yahoo.com (S. Mohan). Corrosion Science 51 (2009) 2139–2143 Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci