Analyses of electrochemical behavior of plasma electrolytic oxidation film on Zirlo alloy in lithium borate buffer solution at 25–300 °C

Abstract

The electrochemical behavior of plasma electrolytic oxidation (PEO) film on Zirlo alloy in 25–300 °C lithium borate buffer solution was evaluated by in-situ electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. As the solution temperature rose to a critical value (150 °C), a new relaxation process related to the distinguishable maximum in phase angle vs. frequency curves was observed at medium frequency and became more pronounced with increasing temperature. This relaxation process almost disappeared after a short exposure time under 300 °C. The transition of the relaxation process was closely related to the impedance of PEO film. The new relaxation process was ascribed to the diffusion of corrosion product through the PEO film. In addition, the degradation of the protective properties of PEO film was observed with increasing temperature, which resulted from the enhanced ionic conductivity of doped zirconia under high temperature. Finally, the PEO film hardly changed in morphology and microstructure after in-situ EIS tests at 25–300 °C. • Electrochemical behavior of PEO film was evaluated by in-situ electrochemical impedance spectroscopy. • A new relaxation process was observed at medium frequency. • The new relaxation process was ascribed to the diffusion of corrosion product. • The conduction mechanism of corrosion species through PEO film was analyzed based on a mix-conduction model.