Corrosion Behavior Of Zr-based Bulk Amorphous Alloys

Zr-based bulk amorphous alloys Zr₆₀Al₁₅Ni₂₅, Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 and Zr₆₅Al₁₀Ni₁₀Cu₁₅ were prepared by copper suction casting. The corrosion behavior of three alloys in NaCl and HCl solutions was investigated by immersion experiment, electrochemical corrosion test system,scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) . Effect factors and corrosion mechanism of bulk amorphous alloys were discussed.The results of immersion experiment showed that the corrosion rates of three alloys were very small. The corrosion rates of Zr₆₀Al₁₅Ni₂₅, Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 and Zr₆₅Al₁₀Ni₁₀Cu₁₅ in 10%NaCl solution were 0.0205 g/m2h, 0.028 g/m2h and 0.0338 g/m2h, respectively. The alloy Zr₆₀Al₁₅Ni₂₅ showed the best corrosion resistance due to the smallest corrosion rate. The corrosion rates of Zr₆₀Al₁₅Ni₂₅, Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 and Zr₆₅Al₁₀Ni₁₀Cu₁₅ in 1.0mol/L HCl solution were 0.0251 g/m2h, 0.0066 g/m2h and 0.0144 g/m2h, suggesting that the alloy Zr_52.5Al₁₀Ni₁₀Cu₁₅Be_12.5 exhibits better corrosion resistance in 1.0mol/L HCl solution.The results of polarization curves showed that Zr₆₀Al₁₅Ni₂₅ passived obviously in NaCl solutions. The alloy Zr₆₀Al₁₅Ni₂₅ exhibited lower susceptive to pitting and better pitting corrosion resistance due to more positive pitting potential. The stable passive film formed on surface of the alloy Zr₆₀Al₁₅Ni₂₅, which decreased corrosion rate. The pitting corrosion susceptive and corrosion rates of three alloys increased with increasing the Cl- concentration. According to the SEM micrographs and EDS analysis Zr, Al, Ni dissolved selectively and Cu enriched under passive film in pitting process which decreased the corrosion resistance.Electrochemical impedance spectroscopy (EIS) data measured were fitted by software Zview, the corresponding equivalent circuits were applied to simulate the corrosion process and mechanism of the bulk amorphous in NaCl and HCl solution. Due to the resistance effect of passive film formed on the surface of the alloy Zr₆₀Al₁₅Ni₂₅, the dissolution of the alloy was prevented. More anions were adsorbed on the surfaces of alloys with increasing the potential, which resulted in fast thinning of passive film and pitting at the defect place of the passive film. EIS of Zr₆₅Al₁₀Ni₁₀Cu₁₅ was double capacitance loops in 1.0mol/L HCl solution at potentials -0.397V and -0.297V. The thickness of passive film was enhanced with increasing the potential, which decreased corrosion rate.