Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci Effect of anodic potential on the electrochemical response of passive layers formed on the surface of coarse- and fine-grained pure nickel in borate buffer solutions Arash Fattah-alhosseini a , Majid Naseri b, ⁎ , Seyed Omid Gashti a , Saeed Vafaeian a , Mohsen K. Keshavarz c a Department of Materials Engineering, Bu-Ali Sina University, Hamedan 65178-38695, Iran b Department of Materials Science and Engineering, Faculty of Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran c Department of Mining & Materials Engineering, McGill University, Montreal, Quebec (QC), H3A 0C5, Canada ARTICLE INFO Keywords: Grain refinement Cold deformation Passive layer Electrochemical impedance spectroscopy Mott–Schottky analysis ABSTRACT In the present work, the role of cold deformation and anodic potential on the electrochemical response of pure nickel in borate buffer solutions were investigated. The application of cold deformation gave rise to a more localized microstructure that contained a greater number of fine grains. In order to investigation of the elec- trochemical response of specimens, potentiodynamic polarization (PDP), electrochemical impedance spectro- scopy (EIS), and Mott–Schottky (M–S) analysis were performed. As a result, with increasing of applied potential, the polarization resistance and passive film thickness decreased. Also, density of electron acceptor at passive layer decreased by increasing of applied potential. 1. Introduction Various methods for enhancement of the corrosion resistance of metals and alloys have been developed within the past three decades. Some of the most interesting and important of them, involve the pas- sivity phenomenon and with so called passive metals. Such widespread interest was provoked by the complexity and practical importance of passivity for increasing the corrosion resistance of metals and alloys [1]. The general opinion expressed in the scientific literature clearly indicates that not all cases of improved corrosion behavior can be considered as being caused by passivity. Analysis of numerous examples of passivity shows that in all cases of improved corrosion resistance, there is a sharp increase in inhibition of the anodic process. Therefore, it is logical to define passivity on the basis of the controlling factor in the corrosion system [2]. The most fundamental and generally accepted theories of passivity at present are those explaining the passive state on the basis of a film or an adsorption mechanism accounting for inhibi- tion of anodic dissolution [3,4]. They describe improved corrosion behavior through the formation of a protective oxide layer on the surface of a metal. This layer is usually thin, transparent, and consists of the metal oxide compound. It is well known that a reduction in the grain size of a pure metal or alloy will influence the mechanical properties of the bulk material. The work of Hall [5] and Petch [6] resulted in the relation of the yield strength of a polycrystalline material to its grain size. In other words, significant gains in strength can be generated simply by re- ducing grain size. This increase in the strength is attributed to dis- location pile-ups. In fact, the greater number of grain boundaries resulting from grain refinement act as extra barriers to dislocation motion and causes dislocations to pile up against the grain bound- aries [7,8]. Other mechanical properties, including hardness, coeffi- cient of friction, and wear resistance, also benefit from grain re- finement. Despite the positive role of grain refinement operation on the mechanical behavior of metals and alloys has been confirmed, yet, its effect on the electrochemical response is not straightforward and rather a complex relation. Nickel is one of the main building blocks of several commercial alloys, which are mostly used in applications that corrosion re- sistance is essential. Therefore, the anodic dissolution of nickel and its passive response has received a certain amount of attention [9,10]. The typical anodic potentiostatic curve in aqueous electro- lytes shows that nickel dissolution occurs in an active of region but is https://doi.org/10.1016/j.corsci.2017.11.016 Received 8 February 2017; Received in revised form 28 October 2017; Accepted 10 November 2017 ⁎ Corresponding author. E-mail addresses: majid_na3ri@yahoo.com, m-naseri@phdstu.scu.ac.ir (M. Naseri). Corrosion Science xxx (xxxx) xxx–xxx 0010-938X/ © 2017 Elsevier Ltd. All rights reserved. Please cite this article as: Fattah-alhosseini, A., Corrosion Science (2017), http://dx.doi.org/10.1016/j.corsci.2017.11.016