The study of plasma electrolytic oxidation coatings on Zr and Zr-1% Nb alloy at thermal cycling

The coatings with a thickness more than 100 μm were formed on Zr-1% Nb alloy and technical pure Zr by plasma electrolytic oxidation (PEO) in silicate-hypophosphite electrolyte at asymmetric electrical mode. It was found that the PEO coating thickness on Zr-1% Nb alloy is about 30% more than that on zirconium. The barrier layer for Zr-1% Nb alloy is not regular and has metallic inclusions. For zirconium, barrier layer is uniform and dense. The plasmatron high-temperature cycling (up to 2000 K) has shown that the coatings surface keeps original microstructure but its morphology becomes some rougher. The thermal conductivity of PEO coatings is several times less than the one of reference sample of yttria-stabilized zirconia.