Abstract

Plasma electrolytic oxidation (PEO) film was fabricated on Zr3Al based alloy. In-situ 768 h electrochemical impedance spectroscopy tests of bare and PEO coated Zr3Al based alloys were performed in 300°C/14 MPa lithium borate buffer solution. The results indicated that the impedance of PEO film was higher than that of bare Zr3Al based alloy in high temperature and high pressure lithium borate solution. Due to the partial chemical dissolution of outer layer, the impedance of outer layer of PEO film decreased while the impedance of inner layer increased until the end of 768 h exposure time. The uniform compact inner layer played a key role in improving the corrosion resistance of Zr3Al based alloy. Mott-Schottky analysis revealed that both passive film and PEO film on bare Zr3Al based alloy had n-type semiconductor feature, corresponding to oxygen vacancies or zirconium/aluminum interstitials. The high defect density in film reduced impedance after a critical exposure time. In addition, the PEO film with high flat-band potential had lower electron transfer capability, which was also beneficial to improving the corrosion resistance of Zr3Al based alloy.

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