Unipolar plasma electrolytic oxidation: Waveform optimisation for corrosion resistance of commercially pure titanium. Issue 6 (8th December 2020)

• Record Type: Journal Article
• Authors: Casanova, Luca; Vicentini, Livio; Pedeferri, MariaPia; Ormellese, Marco
• Is Part Of: Materials and corrosion. Volume 72:Issue 6(2021)
• Page Start: 1091
• Page End: 1104
• Publication Date: 2020-12-08
• Subjects: corrosion -- plasma electrolytic oxidation -- spark -- sulphuric acid -- titanium; Materials -- Periodicals; Metals -- Periodicals; Corrosion and anti-corrosives -- Periodicals; 620.1122305
• DOI: 10.1002/maco.202012198
• Languages: English
• ISSNs: 0947-5117

Abstract

Abstract: 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. Abstract : This study describes recent advances in unipolar plasma electrolytic oxidation applied on commercially pure titanium in a solution of 0.5‐M H2 SO4, highlighting the effect of voltage, duty cycle and frequency. It was verified that using 220 V with a duty cycle containing 90% of anodic polarisation at 1000 Hz favours the development of an orange‐like plasma, enhancing the oxide growth rate and ruling corrosion resistance.