The corrosion behaviour of Zr-based bulk metallic glasses in 0.5 M NaCl solution

Abstract

The corrosion behaviour of eutectic Zr 50Cu 40Al 10 and hypoeutectic Zr 70Cu 6Al 8Ni 16 bulk metallic glasses (BMGs) was studied by electrochemical measurements, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). Zr 50Cu 40Al 10 BMG was highly susceptible to pitting corrosion in naturally aerated 0.5 M NaCl solution at 30 °C. In contrast, Zr 70Cu 6Al 8Ni 16 BMG passivated spontaneously under the same condition. EDX results for Zr 50Cu 40Al 10 indicated that enrichment of Cu, Cl and O occurred in the pitted region, while for Zr 70Cu 6Al 8Ni 16 BMG, no significant difference was found in the surface composition from the specimens before and after immersion in the solution. XPS analysis including angle-resolved measurements for Zr 70Cu 6Al 8Ni 16 BMG revealed that zirconium cation (Zr 4+) was highly concentrated in both air-formed and passive films. Furthermore, the concentration of Zr 4+ ions after immersion for 24 h or more showed tendency to increase with decreasing take-off angle, indicating that the exterior part of the passive film consisted exclusively of zirconium oxyhydroxide. The high corrosion resistance of Zr 70Cu 6Al 8Ni 16 BMG was attributed to the formation of homogeneous and stable passive film enriched with zirconium.