Effect of Nb substitution for Cu on glass formation and corrosion behavior of ZrCuAgAlBe bulk metallic glass

• The addition of Nb deteriorates glass-forming ability.
• Substitution of Nb for Cu improves corrosion resistance in various solutions.
• Dissolve of Cu is the main contribution to corrosion in Cl−-contained solution.
• Substitution of Nb for Cu decreases the pitting nucleation site.
• Nb2O5 is stable in Cl−-contained solution restraining Cu dissolve.

The influence of Nb substitution for Cu on glass forming ability and corrosion behavior in ZrCuAgAlBe alloy was systematically studied. It was found that although Nb addition deteriorated glass forming ability and thermal stability, corrosion resistance, which was evaluated by both potentiodynamic polarization and immersion tests, was improved in 0.5 M NaCl, 0.1 M HCl and 0.5 M H2SO4 solutions. X-ray photoelectron spectroscopy depth profiles on the polished specimens revealed that Nb addition promoted the oxidation of Zr and resulted in thicker oxide film with high valence. Meanwhile, composition analyses before and after immersion in 0.5 M NaCl demonstrated that Cu had a strong affinity for reacting with chloride ions, causing the pitting susceptibility, and the substitution of Nb for Cu not only decreased the pitting nucleation site but also restrained the dissolve of Cu significantly through the passive film. As the immersion time was further prolonged, oxygen content in surface film increased remarkably, and only the fraction of Nb among all metallic elements rose, suggesting that the stability of Nb2O5 in chloride-containing solutions is crucial to improving corrosion resistance.

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