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COMPARISON OF THE CORROSION BEHAVIOR OF A BULK AMORPHOUS METAL, Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 , WITH ITS CRYSTALLIZED FORM

- Nov 30, 2018 -

In both aqueous solutions, the anodic and cathodic potentiodynamic polarizations do not reflect the

growth or reduction of oxidized species on the surface of the alloys. However, considering the Pourbaix

diagrams for the pure constituent metals (20), and the behavior of titanium (21) and zirconium (22) in

other alloys, an oxide film is most likely formed on the alloy surface. In addition, preliminary Auger

electron spectroscopy results suggest that all components of the Zr-Ti-Cu-Ni-Be alloy are present in the

air-formed oxide.

While an oxide film is most likely present during anodic polarizations, the amorphous phase (with

a pitting potential of DF pit ; 12 mV) is only slightly more resistant to pitting corrosion than the

crystalline alloy (DF pit ; 2227 mV); in addition, it does not exhibit the superior corrosion resistance

observed in other amorphous alloys (4–7). The pitting potential of the amorphous alloy may also be

compared to that of zirconium and titanium, which have the largest elemental weight fractions in the

alloy. For example, pure titanium has superior pitting resistance in air-saturated, 1N NaCl, in which

corrosion pits nucleate between 11.2 V and 11.6 V (SCE) (23). On the other hand, pure zirconium in

aerated 0.5 M NaCl has a pit nucleation potential (obtained galvanostatically) of ;160 mV (SCE) (24,

25), which is only slightly more resistant to pitting than the amorphous metal. Comparing the pitting

potential of the amorphous metal to the crystalline metal of the same composition, to pure zirconium,

and to pure titanium, it is clear that the amorphous metal does not have superior resistance to pitting

corrosion in sodium chloride. In addition, the similar values of anodic current in the sodium perchlorate

solution suggest that the amorphous alloy is no more resistant to general corrosion in sodium

perchlorate than the crystalline material. From the values of pitting potential and anodic current, it can

be inferred that the oxide films formed in sodium perchlorate and sodium chloride solutions do not give

amorphous Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 superior corrosion properties; the corrosion properties of the

amorphous metal more likely result from slow repassivation at sites of film damage (14,15).

Conclusions

Based on the results of the potentiodynamic polarizations of crystalline and amorphous electrodes of the

bulk amorphous metal alloy, Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 , in 0.5 M NaCl and 0.5 M NaClO 4 solutions,

it can be concluded that the amorphous structure is only slightly more resistant to pitting corrosion than

the corresponding crystalline structure in NaCl, and is no more resistant to general corrosion in NaClO 4 .

Thus, the homogeneity of the surface of the amorphous phase per se does not significantly improve the

resistance of the Zr 41.2 Ti 13.8 Cu 12.5 Ni 10 Be 22.5 (at%) alloy to general or localized corrosion.