Investigation on the effect of frequency and duty cycle on nano-crystalline TiO2 coatings produced by plasma electrolytic oxidation

Nano crystaline TiO2 coating was produced on commercial pure titanium surface by plasma electrolytic oxidation (PEO) process under constant current condition with 1000 and 1500 Hz frequency, 10 and 15 % duty cycle in 10 min. Surface structure and chemical composition analysis for coatings were conducted by scanning electron microscope and x-ray difracrometer. Corrosion behavior of base metal and coatings was investigated by potantiodynamic polarization in 3.5% NaCl solution. Phase analyses of coatings indicated the presence of titanium oxide in the form of anatase and rutile. Surface of all coated samples had a Pancake porous structure with different pore diameters due to the difference in applied frequencies and duty cycles. Microscopic images of coatings in large magnifications showed the existence of nano-size crystalline (less than 50nm). Investigation on corrosion behavior showed that using high frequency in this process results in increase in corrosion resistance, decrease in current density and increasing the protection efficiency up to 95%.