Corrosion Behavior of Plasma-Sprayed Al2O3-3%TiO2 Coatings Doped with CeO2

Coatings of Al2O3-3%TiO2 (AT3) and CeO2-doped Al2O3-3%TiO2 (1 wt% and 5 wt%) were prepared by plasma spraying. Scanning electron microscopy revealed that CeO2 was mainly distributed in the crevices and between the splat layers of the coating, filling the voids or spaces, and reducing the porosity of the coating. The coating phase was predominantly α-Al2O3, and the addition of rare earth oxide reduced the formation of γ-Al2O3 in the coating. Cyclic polarization measurements showed that the pitting loop did not appear in the cyclic polarization curve of the coating when the rare earth oxide CeO2 content increased to 5 wt%, and the current density of the backward scanning was lower than that of the forward scanning. The results confirmed the higher compactness of the AT3 + 5%CeO2 structure, which can prevent the penetration of chloride ions, thus avoiding pitting. The electrochemical impedance spectroscopy results showed that the amplitude of the low-frequency impedance of Al2O3-3%TiO2-5%CeO2 was the highest compared to other coatings, which confirms that its corrosion resistance is the best in solution. The results of Mott–Schottky measurements showed that the number of gaps in the passive film of the coating decreased with CeO2 doping. With the increase of the doped rare earth content, the capacitance of the ceramic coating increases, which reduces the corrosion rate and improves the corrosion resistance of the coating.