An insight into the evolution of corrosion resistant coatings on titanium during bipolar plasma electrolytic oxidation in sulfuric acid. (20th May 2021)

• Record Type: Journal Article
• Authors: Casanova, Luca; La Padula, Marcello; Pedeferri, MariaPia; Diamanti, Maria Vittoria; Ormellese, Marco
• Is Part Of: Electrochimica acta. Volume 379(2021)
• Publication Date: 2021-05-20
• Subjects: Titanium -- Sulfuric acid -- Eis -- Acid corrosion -- PEO; Electrochemistry -- Periodicals; Electrochemistry, Industrial -- Periodicals; 541.37
• DOI: 10.1016/j.electacta.2021.138190
• Languages: English
• ISSNs: 0013-4686

Abstract

Highlights: Anodization of Ti was performed using a pulsed bipolar waveform in 0.5 M H2 SO4 . Morphology and thickness were controlled by frequency and cathodic polarization. Thickness and compactness favor resistance towards localized corrosion. Thickness and rutile content influence resistance in acidic environments. A novel coating outperforming Ti grade 7 corrosion resistance in H2 SO4 is proposed. Abstract: This work describes recent progress related to bipolar pulsed plasma electrolytic oxidation (PEO) applied to grade 2 titanium in 0.5 M H2 SO4 . Corrosion resistance of oxide coatings was characterized by anodic polarization, immersion tests in acidic environment and electrochemical impedance spectroscopy (EIS). Scanning electron microscope (SEM), X-ray diffraction (XRD), glow discharge optical emission spectroscopy (GD-OES) and visual observation were employed to describe oxide microstructure and composition. The influence of frequency and amount of cathodic polarization were rationalized in terms of modification of the electrical double layer (edl) formed at the oxide-electrolyte interface. Depending on its characteristics, different plasma regimes are established, leading to the growth of oxides optimized for corrosion resistance in different environments. It is here shown how the selection of high frequency (1000 Hz) and a negative-to-positive charge ratio (R) of 0.78 favors the establishment of a strong plasma regime, promoting the growth of a coating optimized for corrosion resistance in concentrated H2 SO4 . It is also reported that low frequency (20 Hz) and cathodic polarization ( R = 0.07) should be used to enhance localized corrosion resistance. Graphical abstract: Image, graphical abstract