Anodic polarization behaviour of Ni60Nb40 and Ni55Cr5Nb40 glasses

Abstract

The corrosion behaviour of Ni60Nb40 and Ni55Cr5Nb40 metallic glass alloys in a 0.1 M H2SO4 solution has been investigated. Anodic polarization curves of these alloys suggest that a protective film is always present on the surface of the alloys. The thickness of this passive film was found to increase with increasing time. The open-circuit potential shifts in the noble direction on the replacement of 5 at.% Ni in the Ni60Nb40 glass by chromium and the transpassive stage is reached at +1500 mV with respect to a saturated calomel electrode for both the metallic glasses. This transpassivity of amorphous NiNb alloys was not expected in view of the stable nature of the niobium film. Auger electron spectroscopy of the passive film on these metallic glasses was carried out to obtain information about the thickness and composition of the passive film at various polarization potentials. The improved corrosion resistance of Ni55Cr5Nb40 glass is due to the formation of hydrated chromium oxyhydroxide film, which contains chromium in excess of the alloy chromium content. © 1987.