Influence of the crystallographic orientation on the electrochemical reactivity measured by Scanning Electrochemical Microscopy on nickel-based alloy 600

The electrochemical reactivity of Alloy 600 in the passive state was examined at the microstructural scale using a local-probe technique, the Scanning Electrochemical Microscopy (SECM). The complementarity of two modes of recording, the current maps and the approach curves, was demonstrated. This study allowed the qualitative determination of high-reactivity zones, but also the quantitative definition of kinetic and thermodynamic parameters, namely the intrinsic kinetic constant and the charge-transfer coefficient. Furthermore, the crystallographic orientation of the studied grains was determined by Electron Backscatter Diffraction (EBSD). The quantitative parameters obtained by SECM were thus assigned to specific crystallographic planes, revealing a relation between the crystallographic orientation of the grains and the reactivity measured on the passive film. The intrinsic kinetic constant increased with the misorientation angle between the grain normal and the < 111 > direction, which reveals the passive film anisotropy. These results show that the coupling of these two techniques is promising for the development of quantitative kinetic or corrosion models. (C) 2019 Elsevier Ltd. All rights reserved.