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Analytical and electrochemical study of passive films formed on nickel—chromium alloys: Influence of the chromium bulk concentration
Author(s) -
Boudin S.,
Vignes JL.,
Lorang G.,
Da Cunha Belo M.,
Blondiaux G.,
Mikhailov S. M.,
Jacobs J. P.,
Brongersma H. H.
Publication year - 1994
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740220198
Subject(s) - chromium , x ray photoelectron spectroscopy , nickel , alloy , auger electron spectroscopy , materials science , hydroxide , analytical chemistry (journal) , low energy ion scattering , oxide , metal , metallurgy , inorganic chemistry , chemistry , chemical engineering , physics , chromatography , nuclear physics , engineering
Depth composition and chemical states of elements constituting the overlayers of Ni x Cr 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 Cr 2 O 3 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 Cr 2 O 3 . Only at high bulk chromium contents (> 15 at.%) are complete Cr 2 O 3 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.