Electrochemical characteristics of Ti-6Al-4V after plasma electrolytic oxidation in solutions containing Ca, P, and Zn ions

Abstract

The electrochemical characteristics of Ti-6Al-4V after plasma electrolytic oxidation (PEO) in solutions containing Ca, P, and Zn ions were studied using various experimental techniques. A Ti-6Al-4V ELI disk was used as a substrate for plasma electrolytic oxidation. A pulsed DC power supply was used to apply a potential of 280V in the electrolyte for 3min. To analyze the electrochemical properties of the PEO film as a function of the Zn content, potentiodynamic and AC impedance tests were carried out with a potentiostat (Model 2273, EG&G Co., USA) using a 0.9% NaCl solution. To examine the bioactivity, the PEO films formed on the specimens and the untreated Ti-6Al-4V specimens were immersed in a simulated body fluid (SBF) for 12h. The PEO-treated and SBF-immersed surfaces were observed by X-ray diffraction, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, and attenuated total reflectance Fourier transform infrared spectroscopy.The number of pores in the PEO films increased, whereas the pore size decreased slightly, as the Zn ion concentration increased. The corrosion potential of the PEO-treated films decreased, while the corrosion current density increased slightly, as the Zn content increased. As shown by the Nyquist plots, the semicircular region in the profile of the Ti-6Al-4V specimens increased compared to that of the other specimens. The films obtained after PEO treatment in the solution containing Zn showed Warburg impedance characteristics. Bone-like apatite was well-formed in specimens of PEO films treated in solutions containing Zn ions at concentrations of 0, 5, and 10mM%. However, formation of the bone-like apatite decreased in specimens of the PEO films treated in a solution containing Zn ions at a concentration of 20mM%.