Abstract
The electrochemical behavior of the oxide layers on two metal-metal glassy alloys, Fe78Co9Cr10Mo2Al1 (VX9)and Fe49Co49V2 (VX50) (at.%), were studied using electrochemical techniques including electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and cyclic polarization (CP) measurements. The morphology and composition of the alloy surfaces were investigated using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion rate and surface roughness of both alloys increased as the concentration of NaOH in aqueous solution was raised. The presence of some protective elements in the composition of the alloys led to the formation of a spontaneous passive layer on the alloy surface. The higher resistance values of both alloys were associated with the magnitude of the dielectric properties of the passive films formed on their surfaces. Both alloys are classified as having outstanding resistance to corrosion, which results from the formation of a passive film that acts as an efficient barrier to corrosion in alkaline solution.
Highlights
The glassy alloys are considered to be particuarly interesting metallic materials because of exceptional properties, or combinations of physical and chemical properties, that distinguish metallic glassy alloys from conventional crystalline materials [1]
The passive film formed on the VX50 alloy surface consisted of two layers (Fig 1(b’))
Fe ions are able to migrate faster through the inner film from the alloy at high NaOH concentration and Fe oxides are preferentially dissolved at the outer film, while Cr remains enriched in the passive film on the side of the alloy surface [16]
Summary
The glassy alloys are considered to be particuarly interesting metallic materials because of exceptional properties, or combinations of physical and chemical properties, that distinguish metallic glassy alloys from conventional crystalline materials [1]. Resistance and passivation behaviour of new Fe-Co metal-metal glassy alloys engineering properties such as good ductility, high toughness and the inherent brittleness of the BMGs. Fe-based BMGs are amorphous structures with unique physical and chemical properties. Gong et al [12] investigated the corrosion behavior of Fe65.5Cr4Mo4Ga4P12C5B5.5 (at.%)bulk metallic glass in 3.0M NaOH solution They found that the corrosion resistance of this alloy was better than its structural relaxation/crystallization counterparts. The (Fe44.3Cr5Co5Mo12.8Mn11.2C15.8B5.9)98.5Y1.5 bulk glassy alloy was studied in very basic solution (1.0M NaOH) by Gostin et al [13] This alloy exhibited a lower corrosion rate at higher pH. Alloy resistivity can be explained according to the composition of the protective film formed in alkaline media, and the properties of these alloys make them very attractive for industrial application
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