Electrochimica Acta 76 (2012) 389–393 Contents lists available at SciVerse ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta The high throughput electrochemical screening of the corrosion resistance of Ni–Cr thin film alloys Talal A. Aljohani, Brian E. Hayden ∗ , Alexandros Anastasopoulos Department of Chemistry, University of Southampton, Southampton SO17 1BJ, United Kingdom a r t i c l e i n f o Article history: Received 19 March 2012 Received in revised form 9 May 2012 Accepted 10 May 2012 Available online 17 May 2012 Keywords: Corrosion High throughput Polarisation resistance PVD Thin films Ni–Cr alloys a b s t r a c t The corrosion behaviour of a series of NiCr thin film alloys were characterised through the high- throughput electrochemical measurement of their polarisation resistance on a micro-fabricated array of electrodes. The linear polarisation resistance (LPR) method has been compared to the results from Tafel extrapolation, and the alloy compositional dependence of the polarisation resistance as a function of composition is consistent. There are, however, some systematic differences in the absolute values extracted using the two methodologies which are likely to be a result of the smaller current densities associated with the LPR method. In the case of the NiCr alloys deposited at 300 K, the observed bulk phases closely agree with those expected from the literature. The polarisation resistance behaviour is shown to be directly related to the bulk alloy structures. Besides the b.c.c. -Cr(Im3m) phase and its Ni solid solutions which exhibit the highest polarisation resistances, the -Cr 3 Ni 2 (P4 2 /mnm) phase exhibits the next best polarisation resistance, and its co-existence with the -Cr 7 Ni 3 (P4 2 /mnm) phase at higher Cr content results in a lowering of that resistance. © 2012 Elsevier Ltd. All rights reserved. 1. Introduction Combinatorial or high-throughput methods have been widely applied to the screening and optimisation of metal alloy [1] and supported metal nano-particle electrocatalysts [2]. Recently, the combinatorial approach has been implemented for the purpose of investigating the corrosion behaviour of materials [3,4]. A scan- ning droplet cell [5] was successfully employed to investigate the passivation behaviour of some thin film alloys [3,6–8]. A optical screening method has been used to assess corrosion behaviour of library of thin films by image analysis of electrodes before and after exposure to the corrosion environment [4]. A multi-electrode method has been applied to evaluate corrosion behaviour before and after adding inhibitors: Pairs of identical wires embedded in an insulator are interrogated by applying potentials which activate both anodic and cathodic responses [9,10]. In the present study we have adapted the high throughput screening methodology employing multi-channel current follow- ers [11] and a silicon micro-fabricated array of independently addressable electrodes [1] to the screening of corrosion char- acteristics of thin film materials. The screening methodology is compatible with the high-throughput PVD methodology based on MBE sources [12] allowing the controllable deposition of ∗ Corresponding author. Tel.: +44 02380592776; fax: +44 02380593781. E-mail address: beh@soton.ac.uk (B.E. Hayden). compositional gradients of a large range of thin film materials. The method has been applied to the study of a library of Ni–Cr alloys in order to assess the effectiveness of this high-throughput approach. 2. Experimental Ni–Cr binary alloy thin films were prepared using a High Throughput Physical Vapour Deposition (HT-PVD) method described in detail elsewhere [12]. A compositional gradient of the alloy was synthesised by simultaneously depositing the two elements Cr (Alfa Aesar 99.99% purity) and Ni (Alfa Aesar 99.95% purity) from electron beam sources with the substrate at 300 K, allowing the complete mixing of elements (kinetically controlled), minimising surface segregation and eliminating any need for post-deposition annealing. The cryo-pumped UHV chamber had a base pressure of 1 × 10 -10 mbar. The two e-beam sources were arranged in a 120 ◦ geometry. Thin films were deposited on two substrates. A 32 mm 2 silicon/silicon nitride substrates (Nova Electronic Materials) were employed for X-ray diffraction (XRD) using a Bruker D8 powder diffractometer with a C2 area detec- tor. A (10 × 10) silicon micro-fabricated array of independently addressable working electrodes (Ilika Technologies Ltd.) was used for the high throughput combinatorial electrochemical screening of the alloys. Composition analysis by Electron Dispersive X-ray Spectroscopy (EDS) using a JEOL JSM5910 and Oxford Instruments INCA 300 was also carried out on these substrates. Details regard- ing the design and fabrication of these arrays, and the principles 0013-4686/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.electacta.2012.05.045