Formation of zirconia tetragonal phase by plasma electrolytic oxidation of zirconium alloy in electrolyte comprising additives of yttria nanopowder

The structure and composition of ceramic coatings formed by plasma electrolytic oxidation (PEO) of Zr-1% Nb alloy under AC conditions in silicate-hypophosphite electrolyte with additives of yttria nanopowder have been analyzed by scanning electron microscopy, X-ray microanalysis and XRD analysis. The yttria nanopowder in electrolyte leads to formation of additional thin superficial layer enriched in conglomerates of Y2O3 nanoparticles. The yttria leads to inhibition of low-temperature m-ZrO2 phase in PEO coating. After addition of 6 g/L yttria nanopowder in the electrolyte only t-ZrO2 phase was found in the coating surface layer. The excess part of Y2O3 nanoparticles is not involved in the PEO process of zirconia formation and remains in the PEO coatings in the form of inclusions.