The plasma electrolytic oxidation (PEO) coatings to enhance in-vitro corrosion resistance of Ti–29Nb–13Ta–4.6Zr alloys: The combined effect of duty cycle and the deposition frequency

In this study, the TiO2-matrix coatings including hydroxyapatite (HA) and tricalcium phosphate (TCP) were successfully deposited on the β-type Ti–29Nb–13Ta–4.6Zr alloys by plasma electrolytic oxidation (PEO) process to enhance the in-vitro corrosion resistance of the alloys. An electrolyte containing calcium hydroxide (CaOH) and sodium phosphate dodecahydrate (Na3PO4·12H2O) were used to prepare micro-arc oxidized samples. The effect of duty cycle, deposition frequency, coating thickness, and surface morphologies have been discussed in the view of corrosion phenomena. The coated morphologies were characterized with scanning electron microscopy (SEM) equipped with energy dispersive spectroscopy (EDS). The corrosion behaviors of the coatings were investigated using potentiodynamic polarization scanning (PDS) technique in Ringer's solutions at body temperature. In addition, the immersion tests on the coated and uncoated samples were performed to observe the apatite phase formation on the surface. X-ray diffraction technique (XRD) has been used in order to determination Ca- and P-based phases on the surfaces. It was found that the corrosion rates of the all coated samples were approximately 4–14 times lower than the uncoated TNTZ sample. The highest resistant coating to corrosion was obtained in the oxidized TNTZ samples deposited at 500 Hz with 30% duty cycle by PEO.