Development of Electrochemical Surface Treatment to Visualize Critical Corrosion-Inducing Inclusions of Zr in Chloride Environments

Abstract

An electrochemical surface treatment was developed to visualize the corrosion-inducing inclusions of Zr in chloride environments. Pure Zr and Zr alloy (Zr–0.5O–0.5C) were evaluated in this study. The electrochemical surface treatment consisted of repeated galvanostatic anodic polarization and potentiostatic cathodic polarization. After the electrochemical surface treatment, only one brittle and non-conductive shell of Zr oxide was observed at the corrosion initiation site on the tested surface. The corrosion-inducing inclusions were found inside the corrosion pit under the optimum polarization conditions. At the corrosion initiation site on pure Zr, the area inside the corrosion pit contained larger amounts of O, C, and Si than the surrounding matrix. In the case of the Zr-0.5O–0.5C alloy, relatively larger inclusions were observed after the treatment. Extremely large amounts of Si, together with O and C, were present in the inclusions. The inclusions that induced localized corrosion on the pure Zr and Zr-0.5O–0.5C specimens were found to be precipitated, involving the specific aggregation of Si. The surface treatment developed in this study is expected to be utilized as a powerful tool to elucidate the localized corrosion mechanism of Zr in chloride environments.