Resistivity and Passivity Characterization of Ni-Base Glassy Alloys in NaOH Media

Abstract

Resistivity and passivation behavior of two Ni-base bulk metallic glasses, with the nominal composition of Ni 70 Cr 21 Si 0.5 B 0.5 P 8 C ≤ 0.1Co ≤ 1Fe ≤ 1 (VZ1) and Ni 72.65 Cr 7.3 -Si 6.7 B 2.15 C ≤ 0.06Fe 8.2 Mo 3 (VZ2), in various concentrations of NaOH solutions were studied. The investigations involved cyclic polarization (CP), electrochemical impedance spectroscopy (EIS), and electrochemical frequency modulation (EFM) methods. Cyclic polarization measurements showed spontaneous passivation for both Ni-base glassy alloys at all alkaline concentrations, due to the presence of chromium as an alloying element that formed an oxide film on the alloy surface. The EIS analysis showed that the passive layers grown on the two Ni-base glassy alloy surfaces are formed by a double oxide layer structure. Scanning electron microscope (SEM) examinations of the electrode surface showed Cr, Ni, Fe, and O rich corrosion products that reduced the extent of corrosion damage. Atomic force microscopy (AFM) imaging technique was used to evaluate the topographic and morphologic features of surface layers formed on the surface of the alloys.