Electrochemical Reactivity of Zirconium-Based Bulk Metallic Glasses

Abstract

ABSTRACTAmorphous Zr-(Ti)-(Nb)-Al-Cu-Ni alloy samples were prepared by melt-spinning and copper mould casting in an argon atmosphere and characterized regarding their microstructure and thermal behavior. Their anodization behavior in aqueous environments with pH= 0.5 – 13 was studied by electrochemical polarization techniques in combination with surface analytical investigations, i.e. SEM/EDX, AES. In chloride-containing solutions the macroscopic corrosion resistance of bulk amorphous alloys is affected by the presence of heterogeneities, such as concentrated cluster zones of selected components or crystalline defects. Pitting phenomena are studied in neutral and acidic chloride solutions and as a result a local corrosion mechanism is proposed. The cathodic reactivity of alloy samples at different microstructural states and after pre-etching in fluoride solutions was investigated. After pre-etching melt-spun amorphous samples exhibit a significant increase in surface reactivity as expressed by a drastic increase in electrochemical capacities and in cathodic current densities as well as by a significant reduction of overpotentials for the hydrogen reduction reaction. The hydrogen sorption behavior was studied on samples galvanostatically charged at various cathodic current densities by means of XRD, DSC, TEM and thermal desorption analysis TDA. At room temperature Zr-based alloys absorb hydrogen up to H/M=1.65 mainly by interstitial solution of hydrogen atoms in the amorphous structure. The effect of absorbed hydrogen on the thermal stability and the crystallization behavior is described.