Effect of Structural Defects, Surface Irregularities, and Quenched-In Defects on Corrosion of Zr-Based Metallic Glasses

Abstract

X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed a fully amorphous structure for as-cast bulk metallic glass (BMG) and melt-spun ribbons of Zr 52 Ti 6 Al 10 Cu 18 Ni 14 prepared by copper mold casting and the melt-spinning technique, respectively. For melt-spun ribbons, the wheel-side surface contained a higher concentration of quenched-in defects (air pockets), whereas surface irregularities were noticed in the air side. Fluctuation microscopy indicated more medium-range order for the as-cast structure of BMG than for the melt-spun ribbon, whereas in the BMG, the medium-range order was located more in the central region than in the periphery. Macro-and microcell electrochemical experiments of the BMG along the cross section and macrocell experiments of each side of the ribbons in dilute acidic chloride environments indicated that the corrosion resistance of the BMG decreased with the increase in the medium-range order; the medium-range order, however, was less deleterious than either the surface irregularities or the quenched-in defects from the viewpoint of corrosion. A surface film formed on the metallic glasses in a dilute acidic chloride environment mainly consisted of oxide of zirconium, in which zirconium was present in the Zr +3 , Zr +2 , and Zr + 1 state in the BMG and in the air-side and wheel-side surfaces, respectively.

Comparing the pitting corrosion behavior of prominent Zr-based bulk metallic glasses

“…Previous surface analytical studies revealed that surface films on Zr-based metallic glasses formed naturally in air or under electrolyte exposure consist mostly of Zr oxides and contain additionally small amounts of other valve metals (in their oxide states), e.g., Al, Nb, and Ti. 4,[17][18][19]21,37 Accordingly, the similar E corr values of the glassy alloys studied here are attributed to their similar surface chemistry, i.e., consisting mostly of Zr oxides. Upon further increase in the potential (see Fig.…”

Correlation between corrosion performance and surface wettability in ZrTiCuNiBe bulk metallic glasses

“…In addition, most MGs possess a natural passive oxide layer that gives them an additional good corrosion resistance. A recent work by Vishwanadh et al 5 on Zr-based BMG also pointed out a strong influence of the sample surface morphology or irregularities on corrosion. However, several recent investigations on bulk metallic glasses ͑BMGs͒ made of Zr-based metals demonstrated prevalent pitting corrosion, which is most notorious in limiting applications.…”

Dissolved-Oxygen-Induced Intensive Pitting Corrosion of Amorphous ZrCu Alloys in Thin NaCl Solutions

“…It was suggested that surface topological defects like air pockets played an important role on the corrosion. 7) Not immersion in solution but keeping in air, the formation of ZrO 2 layers at the surface was reported for a-Zr 40 Cu 60 . 8) As mentioned above, the corrosion resistance of ZrCubase amorphous alloys is not so high in the solutions containing the halogen ions more than $10 mM.…”