Study of Coatings Formed on Zirconium Alloy by Plasma Electrolytic Oxidation in Electrolyte with Submicron Yttria Powder Additives

Abstract

Coatings with thickness 40 to 150 μm were formed by plasma electrolytic oxidation (PEO) on the zirconium alloy Zr-1Nb (Zr-1% Nb) in the slurry electrolyte containing 9 g/L Na2SiO3 5H2O, 5 g/L Na(PH2O2) and 6 g/L submicron Y2O3 yttria powder during 60 min under the AC electrical mode at current densities 20; 30 and 40 A/dm2. The surface morphology, structure, composition, and corrosion-protective ability of the formed coatings have been analyzed. At PEO current density 30 A/dm2, a predominantly tetragonal phase of zirconia was formed in coatings. Increasing the PEO current density up to 40 A/dm2 promoted the formation of the coating surface layer containing submicron yttria particles. Electrochemical polarization studies in 0.5% LiOH solution showed that PEO coatings demonstrated high corrosion-protective ability. The dependence of the polarization currents on the PEO current density was found to be inconsequential.

Plasma Electrolytic Oxidation (PEO) Coating on γ-TiAl Alloy: Investigation of Bioactivity and Corrosion Behavior in Simulated Body Fluid

“…Thus, the trend in the Rct of the samples was: uncoated TiAl (49.6 kΩ m 2 ) < 400 V (280.1 kΩ m 2 ) < 450 V (380.2 kΩ m 2 ) < 500 V (456.7 kΩ m 2 ). In this regard, some researchers [80][81][82][83][84][85][86][87][88][89][90][91] have suggested that the substantial corrosion resistance in PEO coatings stems from the thickness of the oxide layer. Therefore, as the voltage rose, a thicker PEO film formed, which causes the penetration rate of the corrosive solution into the substrate to decrease; hence the chemical reactions culminating in the coating formation deaccelerated kinetically and thermodynamically.…”