Effects of alumina nanoparticles concentration on microstructure and corrosion behavior of coatings formed on titanium substrate via PEO process

Plasma electrolytic oxidation (PEO) process was employed to create ceramic coatings on titanium substrate by using silicate-based electrolytes containing different concentrations of alumina nanoparticles (0, 3, 6, and 10 g/lit). The effect of alumina nanoparticles concentration on the morphology, chemical and phase composition of the PEO coatings was investigated by scanning electron microscope, energy dispersive spectrometer, and X-ray diffractometer, respectively. The corrosion behavior of samples was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests. SEM, EDS, and XRD analyses illustrated that alumina nanoparticles incorporated into the coatings and reduced the density and size of the pores. Furthermore, according to the voltage-time responses, presence of alumina nanoparticles in the electrolyte increased the starting time of sparking due to hindrance effect of these particles on the barrier layer formation. It was found that the corrosion resistance rose by increasing the concentration of alumina nanoparticles. The coating which was formed in electrolyte containing 10 g/l alumina nanoparticles possessed the lowest porosity (11.2%) which boosted the corrosion resistance of the substrate from 2.33×104 to 1.26×106 Ω cm2.