The corrosion behavior of amorphous and nanocrystalline Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy A. Gavrilovic ´ ⇑ , L.D. Rafailovic ´ , W. Artner, J. Wosik, A.H. Whitehead CEST Centre of Electrochemical Surface Technology, 2700 Wiener Neustadt, Austria article info Article history: Received 17 February 2011 Accepted 22 March 2011 Available online xxxx Keywords: A. Alloy B. XRD B. Raman spectroscopy B. Polarization C. Amorphous structures abstract The potentiodynamic polarization curves in 0.5 M NaCl solution before and after crystallization of Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy have been studied in relation to the microstructure and alloy composition. It was shown that the corrosion resistance of the alloy strongly depending on these two factors. The observed decrease in corrosion resistance of the alloy after the heat treatment up to 480 °C in comparison to the corrosion resistance of the alloy in the as prepared state is attributed to the increased inhomoge- neity of the alloy that coincides with the first appearance of Fe 3 Si phase. Further heating (up to 600 °C) resulted in an increase in the number of Fe 3 Si nanocrystallites and the appearance of a FeCu 4 phase. After annealing at 600 °C the lowest corrosion rate, 0.004 mm a 1 , was observed. Annealing of the samples at higher temperatures (>600 °C) induced formation of six crystalline phases which proved detrimental to the corrosion resistance of the Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy. Solid corrosion products were identified on the surface of the samples after anodic polarization. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The corrosion resistance of amorphous Fe–B–Si–Nb–Cu alloys is subjected to the specific chemical composition, stability and elemental homogeneity. It is generally known, that amorphous metallic alloys have higher corrosion resistance than crystalline counterparts with similar elemental composition, since they have no grain boundaries or crystalline defects that could act as corro- sion initiation sites. However, the best soft magnetic properties, such as high saturation magnetization and high permeability, are found not in the amorphous but rather the nanocrystalline state of these alloys, which can be obtained by controlled anneal- ing of an amorphous alloy at high temperatures [1–3]. Numerous publications describe superior soft magnetic and mechanical properties of Fe-based amorphous and nanocrystalline materials [4–11]. The corrosion of Fe-based amorphous alloys and its influ- ence on magnetic behavior was also a topic of many investiga- tions [12–18]. There are still broad areas, however, where understanding is incomplete, particularly on the corrosion behav- ior of nanocrystalline Fe-based soft magnetic alloys formed at high annealing temperatures, which exhibit specific phase com- positions and microstructures. Such studies are essential for bet- ter understanding of the corrosion mechanisms of these alloys under normal working conditions and hence improving their practical longevity. In their widespread technological applica- tions, Fe-based nanocrystalline alloys are often exposed to a wet industrial or marine atmosphere that contains chloride ions. In such environments, the corrosion resistance of nanocrystalline ferromagnetic materials generally depends on their microstruc- ture and phase compositions [14,19]. Elevated temperatures in combination with atmospheric corrosion can induce structural transformations of the alloy surface, which lead to deterioration of the physical properties. This can result in sudden, catastrophic failure. Hence, the objective of this work was a detailed investigation of the corrosion properties of a commercial Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy, with respect to the microstructure and phase composition. In 1988, Yoshizawa et al. [20] found that the partially crystal- lized Fe–Si–B amorphous alloys showed a homogeneous and stable nanocrystalline phase by adding small amounts of Cu and Nb. The primary crystallization product was an FCC, Fe–Si phase with about 10 nm crystallite size, embedded in an amorphous matrix. The role of Cu and Nb additions in crystallization and microstructural trans- formations and their further influence on mechanical properties at higher annealing temperatures were the subject of our previous work [21,22]. The appearance of nanocrystalline Fe–Si phase intro- duces heterogeneity in the alloy. It is to be expected that this will change the corrosion resistance. Subsequent phase transforma- tions at higher annealing temperatures (T > 600 °C) produce vari- ous intermetallic compounds [21]. Potentiodynamic polarization curves in 0.5 M NaCl solutions, of the alloy after annealing at given temperatures are reported in relation to the microstructural changes and phase composition. Raman spectroscopy is a powerful surface analysis technique to study different species formed on the alloy surface during corrosion [23–26]. In this work, the Raman method was used ex situ to characterize corrosion products. 0010-938X/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.corsci.2011.03.023 ⇑ Corresponding author. Tel.: +43 (0) 2622 22266 12; fax: +43 (0) 2622 222 66 50. E-mail address: aleksandra.gavrilovic@cest.at (A. Gavrilovic ´). Corrosion Science xxx (2011) xxx–xxx Contents lists available at ScienceDirect Corrosion Science journal homepage: www.elsevier.com/locate/corsci Please cite this article in press as: A. Gavrilovic ´ et al., The corrosion behavior of amorphous and nanocrystalline Fe 73.5 Cu 1 Nb 3 Si 15.5 B 7 alloy, Corros. Sci. (2011), doi:10.1016/j.corsci.2011.03.023