Institute of Сhemistry of Far Eastern Branch of Russian Academy of Sciences, Vladivostok, Russia:

S. V. Gnedenkov, Professor, Deputy Director for Science, Head of Department of Electrochemical Systems and Surface Modification Processes
S. L. Sinebryukhov, Assistant Professor, Head of Laboratory of Non-stationary Surface Processes
D. V. Mashtalyar, Senior Researcher, Laboratory of Biomedical Composite Coatings
I. M. Imshinetskiy, Junior Researcher, Laboratory of Biomedical Composite Coatings, e-mail: igorimshin@gmail.com

For the purpose of corrosion resistance improvement and wear reduction of protective composite coatings, methods of their formation on magnesium alloys were developed using plasma electrolytic oxidation and electrophoresis precipitation of superdispersed polytetrafluoroethylene (SPTFE). There was carried out a complex investigation of electrochemical and tribological characteristics and morphological peculiarities of obtained composite coatings on the MA8 alloy (Mg – Mn – Ce system). There was made a conclusion, that polymer-containing coatings, obtained in suspension with SPTFE concentration of 30 g/l lead to decrease of corrosion current density by three orders of magnitude (I_с = 2,0·10–10 A/сm²), and increase of polarization resistance value by three orders of magnitude (RP = 2,7·108 Om·cm²), as compared to the base PEO-coating. The trend of change of phase angle maximum values to bigger values with increasing polymer concentration points to increasing of coating protection characteristics. According to the result analysis, increasing of polymeric powder concentration in solution up to 30 g/l leads to increasing resistance of both porous and non-porous coating parts. This is explained by incorporation of bigger more amount of polymer in coating surface porous layer, which allows making the polymer surface layer more homogeneous at applied thermal treatment conditions. However, introduction of more than 30 g/l of SPTFE in electrolyte composition leads to degradation of protective characteristics of composite layer. Presence of superdispersed polytetrafluoroethylene in composite coating influences positively on antifriction properties of samples. Polytetrafluoroethylene layer is used as a dry lubricant. At the same time, the best composite polymer-containing coatings decreases the wear by two orders of magnitude (1,2·10–6 mm³/N·m) in comparison with the base coating applied by plasma electrolytic oxidation.

This work was carried out with the support of Russian Scientific fund (No. 14-33-00009) and the Government of Russian Federation (Federal agency of scientific organizations).

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