Analytical and electrochemical study of passive films formed on nickel—chromium alloys: Influence of the chromium bulk concentration
Article first published online: 15 SEP 2004
Copyright © 1994 John Wiley & Sons Ltd.
Surface and Interface Analysis
Volume 22, Issue 1-12, pages 462–466, July 1994
How to Cite
Boudin, S., Vignes, J.-L., Lorang, G., Da Cunha Belo, M., Blondiaux, G., Mikhailov, S. M., Jacobs, J. P. and Brongersma, H. H. (1994), Analytical and electrochemical study of passive films formed on nickel—chromium alloys: Influence of the chromium bulk concentration. Surf. Interface Anal., 22: 462–466. doi: 10.1002/sia.740220198
- Issue published online: 15 SEP 2004
- Article first published online: 15 SEP 2004
Depth composition and chemical states of elements constituting the overlayers of NixCr alloys (x = 0–30 at.%) passivated in borate buffer solutions (pH = 9.2) were determined as a function of the chromium bulk content of the alloy. Depth sputter profiling was performed using both Auger electron spectroscopy (AES) and low energy ion scattering spectroscopy (LEIS). Chemical bonding and (oxy-hydroxy) structures of alloying elements in the passive films were investigated by x-ray photoelectron spectroscopy (XPS). The electrochemical study mainly consists in establishing the cathodic reduction kinetics of the passive layers to characterize the resistance of the internal Cr2O3 barrier to reduction.
Very thin films (less than 2.5 nm) were obtained in those conditions showing duplex structures where minor external nickel oxy-hydroxide layers are depicted covering an inner protective barrier mainly composed of chromium oxide Cr2O3. Only at high bulk chromium contents (> 15 at.%) are complete Cr2O3 layers built at the interface with the metallic alloy. Beneath the film, in the underlying matrix, a metallic nickel enrichment combined with a chromium depletion is observed, which seems to confirm, as for FeCr alloys, a mechanism by which Cr oxidizes preferentially in this medium during the first steps of the film growth.