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SM ISO690:2012 RUDNEV, V., MALYSHEV, I., YAROVAYA, T., NEDOZOROV, P.. On anti-corrosion properties of plasma electrolytic coatings on valve metals. In: Materials Science and Condensed Matter Physics, Ed. 9, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, Ediția 9, p. 258. |
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Materials Science and Condensed Matter Physics Ediția 9, 2018 |
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Conferința "International Conference on Materials Science and Condensed Matter Physics" 9, Chișinău, Moldova, 25-28 septembrie 2018 | |||||
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CZU: 544.6+620.19+66 | |||||
Pag. 258-258 | |||||
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Anodic oxide coatings on valve metals and alloys (Al, Ti, Mg, Zr, Nb, etc.) formed by spark or microarc discharges in the near-anode region (plasma electrolytic oxidation, PEO) are used for anti-corrosion protection of articles [1]. Nevertheless, even now, the search for conditions of forming the PEO-coatings with improved anticorrosion characteristics remains relevant. We investigated the effect of the duration t of the galvanostatic formation on the anticorrosive properties of PEO coatings on the magnesium alloy in the Na2SiO3 + NaOH + NaF electrolyte and on the aluminum alloy in the ZrSO4 electrolyte. The composition and structure of the coatings were studied by X-ray microprobe analysis, X-ray diffraction, and scanning electron microscopy of high resolution. The anticorrosive properties of the coatings were evaluated using a laboratory apparatus described in [2]. The plus of the current source was connected to the bare sample metal across an ammeter, and the minus - to the counter electrode. A drop of 3% solution of NaCl was placed in the gap between the electrodes. Potential difference of 1.5 or 50 V was applied to the electrodes for coatings on magnesium and titanium, respectively. The pitting formation time τp was measured as the interval between the drop touching the surface and the sharp increase of current through the sample. The dependences τp=f(t) obtained in both cases have a pronounced maxima, Figs. 1 and 2. We did not find any correlations between the behavior of the τp = f (t) dependence and the change in composition, thickness and surface porosity of the coatings with the formation time t. A comparison in the behavior of the U = f(t) on electrodes when forming coatings and τp = f(t) curves shows that the peaks of the electric-induced pitting formation on both magnesium and titanium coincide with the region of the PEO process transition from the spark stage to the microarc one. One can assume a similar behavior of the anticorrosion resistance of PEO coatings galvanostatically formed on different valve metals and alloys in electrolytes of different composition. |
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