Abstract
Resistivity and passivation behavior of two Ni-base bulk metallic glasses, with the nominal composition of Ni70Cr21Si0.5B0.5P8C ≤ 0.1Co ≤ 1Fe ≤ 1 (VZ1) and Ni72.65Cr7.3-Si6.7B2.15C ≤ 0.06Fe8.2Mo3 (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.
Highlights
Bulk metallic glasses (BMGs) or glassy metals are considered to be the materials of the future [1].This is attributed to their chemically and structurally homogeneous nature, providing a lack of local electrochemically active sites [2]
The complex plane, and Bode phase plots for the VZ1 and VZ2 alloys were recorded at the open circuit potential (OCP) in 1.0, 3.0, 6.0, 9.0, and 12.0 M NaOH concentrations at 27 ◦ C, in order to estimate the passivation and resistance of studied alloys
The first time constant was recorded at high frequencies (HF), where the properties of electrode/electrolyte interfaces were reflected, and it was displayed as a depressed incomplete semi-circle
Summary
Bulk metallic glasses (BMGs) or glassy metals are considered to be the materials of the future [1]. Ni-base BMG alloy was studied in a different type of aqueous, i.e., boiling of 6 M HNO3 and 6 M HNO3 + 5 g·L−1 Cr6+ solutions [5] They have been intensively studied, especially to further improve their corrosion resistivity property, e.g., the passive films formed on Ni82.3 Cr7 Fe3 Si4.5 B3.2 and Ni75.5 Cr13 Fe4.2 Si4.5 B2.8 in 1.0, 3.0, 6.0, 9.0, 12.0 M HCl, and in 1.0, 3.0, 6.0, 9.0, 12.0 M H3 PO4 [6,7]. The corrosion resistance of the alloys was studied by EIS (electrochemical impedance spectroscopy) measurements, followed by cyclic polarization, in order to study the disruption of surface. The specimens of BMG alloys were evaluated under the same side of the sample was exposed to the corrosive environment (the bright face) as the working electrode. The surface condition and chemical composition of the alloys’ surfaces were examined using a JEOL JSM-6000 scanning electron microscope A digital instrument CP-II (Veeco Instruments), was used for the measurements of the VZ1 and VZ2 alloys
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