Effect of pH and NaF addition on corrosion of Zr-based bulk metallic glass in Na2SO4-containing solution

In order to expand the application of Zr-based bulk metallic glasses (BMGs) in the field of biomaterials, it is vital to investigate their corrosion behaviour in different solution environments. However, until now, the corrosion behaviour of Zr-based BMGs in F--containing solution has been rarely studied, and the corrosion mechanism is not fully understood. In this study, the effect of pH and NaF addition on the corrosion behaviour of Zr52Al10Ni6Cu32 BMG in Na2SO4-containing solution has been investigated by employing the standard electrochemical methods. The relationship between the critical pF value and pH has been subsequently obtained, which provides a criterion for judging the state of corrosion of Zr-based BMGs in F--containing solution. The cathodic reaction mainly involves the reduction of the dissolved oxygen in the solution, and the kinetic mechanism is similar to that of pure Zr. An oxidation peak appearing during the upward polarization scanning is attributed to the active dissolution of Cu caused by SO42- and F-. During upward polarization, different pH values and addition of NaF are observed to result in consequent film breakdown behaviour. For 0.1 M NaF and pH = 8.0, the protective ZrO2 passive film is noted to be replaced by the corrosion product of the Zr-F compound. However, at pH = 4.0 with 0.001 M NaF, the F- concentration is not sufficient to form the Zr-F corrosion products, and the dissolution rate of the passive film is enhanced due to the reduced pH. This study provides a deeper understanding of the corrosion mechanism of Zr-based BMGs alloys in F--containing solution.