Измерение, мониторинг, управление, контроль (Apr 2022)

STUDY OF THE INFLUENCE OF THE MEASURING SIGNAL FREQUENCY ON THE INDIRECT MEASUREMENT ERROR OF OXIDE COATINGS PROPERTIES

  • P.E. Golubkov,
  • Е.А. Pecherskaya,
  • G.V. Kozlov,
  • V.S. Alexandrov,
  • О.А. Melnikov,
  • Т.О. Zinchenko

DOI
https://doi.org/10.21685/2307-5538-2022-1-8
Journal volume & issue
no. 1

Abstract

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Backgroung. The object of the study is the method of indirect measurement of the thickness and porosity of a coating obtained by microarc oxidation based on impedance measurement. The subject of the study is the confirmation of the possibility of indirect measurement of the coating thickness and porosity by measuring the impedance. The purpose of the study is to obtain analytical expressions for indirect measurement of the thickness and porosity of coatings and their experimental verification; to study the influence of the measuring signal frequency on the measurement errors of these quantities. Materials and methods. Oxide coatings were obtained on samples of technical aluminum grade AD31T1 with a size of 23 × 15 × 1.5 mm. Microarc oxidation was carried out in an electrolyte containing 0.5 g/l NaOH and 80 g/l Na2SiO3 in the anode-cathode mode with a ratio of anode and cathode currents equal to 1 at a current density of 11 A/dm2. The processing time was varied from 60 to 600 s. The impedance of the coating was measured in the frequency range from 20 Hz to 10 kHz with an error of ±0.5 % (in resistance and capacitance) using the software – hardware complex developed by the authors. The thickness of the coating was measured using a high-precision Mitutoyo ABSOLUTE Digimatic micrometer. Results. The analytical dependence of the thickness and porosity of the coating on the impedance modulus and the measuring signal frequency is established. It is shown that the impedance argument does not depend on the coating parameters. The obtained dependence adequately describes experimental data in the frequency range from 500 Hz to 10 kHz, while the relative error of indirect measurement of the thickness by the coating impedance is minimal at a frequency of 10 kHz and is ±5 %. Conclusions. The proposed model has limitations related to the difficulty of simultaneously measuring the thickness and porosity of the coating. To eliminate this disadvantage, additional measurement information is required or the inclusion of the obtained expressions in the system of equations. Nevertheless, the proposed theoretical model can be used for measuring one of the parameters (thickness or porosity of the coating) if another parameter or its functional dependence on the parameters of the microarc oxidation process is known.

Keywords