Investigation of zirconia plasma electrolytic oxidation coatings by nuclear backscattering spectrometry

Abstract

Zirconia coatings of a thickness up to 110 μm were obtained by plasma electrolytic oxidation (PEO) in silicate-alkaline and silicate-hypophosphite electrolytes. Layer-by-layer structure and total porosity of the coatings were investigated using proton nuclear backscattering spectrometry (NBS). The PEO coating obtained in the first electrolyte has a thick transition layer with decreasing oxygen content with the depth increasing. The coating formed in the second electrolyte has a thick layer of zirconia and a thin transition layer. When analyzing the NBS spectra, the thickness is determined without taking porosity into account (so called mass thickness). The total porosity of the coatings was evaluated by determining the difference between their geometric and mass thicknesses: 15 and 22%, respectively. The critical load of disruption is higher for the PEO coating formed in the silicate-hypophosphite electrolyte.