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

The corrosion behaviour of eutectic Zr(50)Cu(40)Al(10) and hypoeutectic Zr(70)Cu(6)Al(8)Ni(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(50)Cu(40)Al(10) BMG was highly susceptible to pitting corrosion in naturally aerated 0.5 M NaCl solution at 30 degrees C. In contrast, Zr(70)Cu(6)Al(8)Ni(16) BMG passivated spontaneously under the same condition. EDX results for Zr(50)Cu(40)Al(10) indicated that enrichment of Cu, Cl and O occurred in the pitted region, while for Zr(70)Cu(6)Al(8)Ni(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(70)Cu(6)Al(8)Ni(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(70)Cu(6)Al(8)Ni(16) BMG was attributed to the formation of homogeneous and stable passive film enriched with zirconium. (C) 2011 Elsevier Ltd. All rights reserved.