Journal
MATERIALS AND CORROSION-WERKSTOFFE UND KORROSION
Volume 72, Issue 6, Pages 1091-1104Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/maco.202012198
Keywords
corrosion; plasma electrolytic oxidation; spark; sulphuric acid; titanium
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The study showed that anodisation of titanium grade 2 at high voltage (220 V), high frequency (1000 Hz) and high level of anodic polarisation (90%) can promote the formation of thicker oxides with rough architecture. Additionally, it was verified that this approach is particularly advantageous for localized and uniform corrosion.
This study deals with the anodisation of titanium grade 2 in 0.5-M sulphuric acid using a pulsed signal in a unipolar regime. The electrical parameters investigated are voltage, frequency and duty cycle. The use of duty cycles with a high percentage of anodic polarisation (90%), combined with high frequencies (1000 Hz) and the higher voltage tested (220 V), favoured the establishment of a plasma regime involving strong dielectric discharges, allowing the growth of thicker oxides but with rough architecture. The corrosion resistance of the formed film has been characterised by potentiodynamic tests in 0.5-M NaBr for localised corrosion resistance and by immersion tests in 10% v/v sulphuric acid solution for a uniform corrosion assessment. Current-time curves, visual observations and electron microscope analysis (scanning electron microscopy, energy-dispersive X-ray spectroscopy) were the tools selected to provide a correlation between technological parameters and oxide growth mechanism. For localised and uniform corrosion, anodisation at 220 V with a high level of anodic polarisation (90%) and frequency (1000 Hz) was verified to be particularly advantageous.
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