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

The corrosion behaviour of eutectic Zr50Cu40Al10 and hypoeutectic Zr70Cu6Al8Ni16 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). Zr50Cu40Al10 BMG was highly susceptible to pitting corrosion in naturally aerated 0.5 M NaCl solution at 30 °C. In contrast, Zr70Cu6Al8Ni16 BMG passivated spontaneously under the same condition. EDX results for Zr50Cu40Al10 indicated that enrichment of Cu, Cl and O occurred in the pitted region, while for Zr70Cu6Al8Ni16 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 Zr70Cu6Al8Ni16 BMG revealed that zirconium cation (Zr4+) was highly concentrated in both air-formed and passive films. Furthermore, the concentration of Zr4+ 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 Zr70Cu6Al8Ni16 BMG was attributed to the formation of homogeneous and stable passive film enriched with zirconium.

► EDX results for Zr50Cu40Al10 indicate that enrichment of Cu, Cl and O occurs in pit. ► XPS analysis for Zr70Cu6Al8Ni16 reveals that Zr is concentrated in passive film. ► The exterior part of the passive film consists exclusively of Zr oxyhydroxide. ► High corrosion resistance of 70Zr is due to the stable film enriched with Zr.