Preparation ZrO2 ceramic coating by electrolytic plasma oxidation and study of the effect of monoclinic/tetragonal phases on the corrosion resistance of the coating

In this paper, zirconium oxide ceramics coating (ZrO2) were produced on Zircaloy-4 alloy using plasma electrolytic oxidation (PEO). Sodium silicate and Sodium aluminate based electrolyte was selected in PEO process and the effects of the concentration of Sodium aluminate (0, 2.5, 5, 7.5, and 10 g/L) on the microstructure, phase structure and the behavior of corrosion of formed coatings. In order to examine the morphology and phase structure of coatings, scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used respectively. The corrosion behavior of the coated samples was evaluated by potentiodynamic polarization in 0.5 M LiOH solution. All oxide ceramics showed improved corrosion resistance. The results show that it's the NaAlO2 leads to inhibition of monoclinic ZrO2 phase in PEO coatings and stabilization of the t-ZrO2 phase in the electrolyte of 10g/L NaAlO2 (A10) leads to decrease corrosion current density its up to 1.10*10-7A/Cm2 . After the addition of 10 g/L Sodium aluminate (A10) in the electrolyte %20 tetragonal zirconia was formed on the surface. The improvement in corrosion properties mainly depends on the phase composition of the produced coatings, so that in the electrolyte of 10g/L NaAlO2 (A10) showed the best corrosion resistance in comparison to other coatings.