The effects of cathodic and anodic voltages on the characteristics of porous nanocrystalline titania coatings fabricated by microarc oxidation

Porous nanocrystalline titania films were prepared by microarc oxidation (MAO) of a titanium alloy keeping anodic voltage at 230-410 V and cathodic voltage at 20-45 V in a Na2CO3 and Na2SiO3 electrolytic solutions using an asymmetric pulse alternating current power supply. XRD, EDS and SEM were employed to characterize the phase, composition and microstructure of the films. It is found that the films consist of dominant rutile and little anatase phases. The phase, pore size and thickness of the coatings strongly depend on the applied voltage, consistent with the previous reports, and the cathodic voltage has an intense effect on the films' pitting corrosion performance in sodium chloride solution. The films prepared by keeping the anodic and cathodic voltages at 320 and 45 V, respectively, for 30 min were porous, with 200 nm to 4 μm pores and the pore walls composed of 100-300 nm rutile crystallites.