Frequency-dependent microstructural characteristics and corrosion behavior of oxide coatings on Ti-6Al-4V alloy fabricated by plasma electrolytic oxidation

This study investigated the influence of three different frequencies (100, 1000, and 2000 Hz) during the PEO process on the characteristics of ceramic coatings fabricated on Ti-6Al-4V alloys in the presence of 12 g/L Na3PO4.12H2O and 3 g/L ZrO2 nanoparticles. The microstructure, surface roughness, wettability, chemical composition, and corrosion performance of the coatings were thoroughly examined to assess their performance. The microstructural results revealed that increasing frequencies led to a reduction in the porosity size, as well as a decrease in coating thickness, wettability, and surface roughness. Additionally, the corrosion performance of the coatings was evaluated in Hank's solution using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) methods. As the frequency rose from 100 to 2000 Hz, the corrosion current density dropped significantly from 47.35 to 13.75 nA/cm2 and the corrosion potential increased from 218 to 684 mV versus Ag/AgCl electrode. These findings indicated that the coating produced at a frequency of 2000 Hz exhibited the lowest corrosion density, thereby demonstrating superior corrosion resistance compared to the coatings produced at lower frequencies. The corrosion resistance of the optimum coating (coating formed at a frequency of 2000 Hz) was found to be approximately 0.8 times higher compared to the uncoated metal.