Characterization of Al2O3/ZrO2 composite coatings deposited on Zr-2.5Nb alloy by plasma electrolytic oxidation.

Plasma electrolytic oxidation (PEO) process was employed in a galvanostatic regime on Zr-2.5Nb alloy in NaAlO 2 aqueous electrolyte solutions within a concentration gradient of 5–30 g/L in order to produce Al 2 O 3 /ZrO 2 composite coatings. The composition and microstructure of the oxide layers were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). Vickers microhardness, scratch adhesion and potentiodynamic polarization measurements were used to assess the mechanical and electrochemical properties of the PEO coatings. The experimental findings suggest a strong correlation between the electrolyte concentration and the coating layers. By increasing the concentration of NaAlO 2 in the electrolyte solution, significantly increased tetragonal crystal structure, particle size, hardness, adhesion strength and corrosion resistance occur with pore size decrease. Best values for the hard and adherent coating were ∼1500 HV and ∼60 N critical load. The corrosion current densities for the plasma electrolytic oxidized samples are lower than the black oxide coated Zr alloy. [ABSTRACT FROM AUTHOR]