Synergistic Effect Mechanism of Different Ions on the Electrochemical Corrosion Behavior of TC4 Titanium Alloy

Due to the compact passive film, titanium alloys exhibit excellent corrosion resistance. However, during practical applications, the passive film is inevitably damaged by aggressive ions. Among the common ions, F- is the most harmful to the passive film because of its high complexation with Ti. However, the destructiveness of F- varies with pH. Moreover, there are inhibitory ions that reduce the aggressiveness of F-. The acceleration effects of H+ and F- as well as the inhibition effect of Fe3+ on the corrosion behavior of TC4 alloy were examined in this work using electrochemical polarization curves measurements and electrochemical impedance spectroscopy (EIS). The results reveal that whereas H+ has slight destructive effect on the passive film, F- has a considerable aggressive effect. In particular, F- and H+ work synergistically to accelerate the corrosion of the TC4 alloy. The addition of Fe3+ can somewhat reduce corrosion of the TC4 alloy. This can be attributable to the fact that the faster cathodic reduction caused by Fe3+ moves the anodic curves from active-passive region to passive region. Meanwhile, F- is consumed by forming a compound with Fe3+, which mitigates the corrosive effect of F- on passive film.

Automated summary

Due to its compact passive film, titanium alloys show excellent corrosion resistance. However, the passive film is often damaged by aggressive ions during practical applications. Among these ions, F- is the most harmful due to its strong complexation with Ti. The corrosive effect of F- varies with pH and can be mitigated by inhibitory ions. In this study, the acceleration effect of H+ and F- as well as the inhibition effect of Fe3+ on the corrosion behavior of TC4 alloy were investigated through electrochemical measurements. The findings demonstrate that F- has a considerable aggressive effect while H+ has only a slight destructive effect. Additionally, Fe3+ can reduce the corrosion of TC4 alloy by shifting the anodic curves and consuming F- through compound formation.