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The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing mechanical mixture of zirconia and silica nanoparticles in concentrations of 2, 4 and 6 g/l have been investigated. It has been established by SEM, EDS, and XPS that ZrO2/SiO2 nanoparticles successfully were incorporated into the coatings. Micro-Raman spectroscopy showed the presence of ZrO2 in tetragonal and monoclinic forms in the PEO-coating composition as well as Mg2SiO4 in tetrahedral configuration uniformly distributed in the outer part of coatings. Obtained coatings significantly reduce corrosion current density in comparison with bare Mg alloy and base PEO-layer (from 2.4 × 10–7 A/cm2 for base PEO layer to 0.7 × 10–7 A/cm2 for coatings with nanoparticles). It has been found that the presence of solid nanoparticles in the composition of coating has a positive effect on their hardness (this parameter was increased from 2.1 ± 0.3 GPa to 3.1 ± 0.4 GPa) and wearproof (the wear was reduced from (4.3 ± 0.4)×10–5 mm3/(N × m) to (3.5 ± 0.2)×10–5 mm3/(N × m)).

The morphology, electrochemical and mechanical properties of the protective composite coatings, formed on the magnesium alloy surface by means of plasma electrolytic oxidation (PEO) and fluorocarbon materials have been established. After the treatment of the PEO-coating by fluoroparaffins the impedance modulus and polarization resistance have increased by two orders of magnitude and wear resistance in more than 10 times as compared to the base PEO-layer. Hydrophobic properties of the composite coatings have been established: values of the contact angle changed in the range from 122° up to 137°, depending on the flouroparaffin type.

The paper presents results of the study aimed at assessing the effect of duty cycle (D) during plasma electrolytic oxidation (PEO) on morphology, composition, and protective properties of the coatings produced on 5754 aluminum alloy in a mixed electrolyte. It is shown that increasing the duty cycle of a microsecond current pulses leads to a decrease of porosity and an increase of thickness of the PEO-layers, which are composed of γ-Al2O3, β-Al2O3, AlPO4, and Al2Mo3C. This improved the barrier properties and microhardness of the coating. The Young's modulus increased with an increase of the quantity of electricity due to the changes of morphological and chemical structure of the coatings. The PEO-coatings produced at a higher duty cycle and longer oxidation time are more wearproof as compared to ones formed at a shorter oxidation time and lower D values. The obtained data allowed confirming the hypothesis on phase formation mechanism.

The methods to form protective coatings by the plasma electrolytic oxidation method (PEO) using the superdispersed polytetrafluoroethylene (SPTFE) suspension have been developed. Electrochemical, salt spray corrosion testing, hydrogen evolution, and tribological studies of the composite polymer-containing coatings have been carried out. Models of the coatings structure have been suggested. The obtained results corroborated the increase of the corrosion protection and wear-resistance parameters by more than 4 orders of magnitude for the composite coating in comparison with the base PEO-coating. The fabricated composite coatings are characterised with high antifriction properties due to the presence of polytetrafluoroethylene in the surface layer pores.

The method of the inhibitor-containing coatings formation with self-healing properties on the surface of magnesium alloys has been developed. The obtained experimental results indicate that the protective properties of the samples with inhibitor-containing coating were increased in comparison with the samples without coating and the base coating obtained by plasma electrolytic oxidation method (PEO). Electrochemical parameters of the porous and poreless layers on the surface of the samples have been calculated before and after polarization due to experimental impedance data modeling by means of the equivalent electrical circuits.

The way of self-healing coating formation at the surface of magnesium alloys on the base of plasma electrolytic oxidation method (PEO) has been suggested. Scanning Vibrating Electrode Technique (SVET) and Scanning Ion-Selective Electrode Technique (SIET) were used for determining the kinetics and mechanism of the self-healing process. The treatment of the PEO-layer by the solution containing 8-hydroxyquinoline enables one to decrease the current density of the composite coating in 30 times (3.2 μA cm −2 ) in the corrosion-active environment in comparison with the base PEO-coating (100 μA cm −2 ) and avert the intensive destruction of the material.

In order to increase the hardness and wearproof of magnesium alloy parts it is necessary to use protective coatings. These surface layers were formed by plasma electrolytic oxidation (PEO) in the electrolyte containing nanosized particles of titanium nitride. X-ray photoelectron spectroscopy and Raman spectroscopy showed the presence of TiN, TiOxNy, and TiO2 compounds in the composition of the PEO-layer. Oxidation of TiN in TiOxNy and TiO2 was realized during the PEO treatment. It has been shown that the best protective mechanical properties are attributed to the coatings formed in electrolytes with TiN concentrations of 2–3 g/l. Mechanical properties of the obtained layers have been studied. It has been established that the hardness of nanoparticles-containing coatings is twofold higher in comparison with the PEO-coating formed in the base electrolyte; its wear resistance increases in 2.2 times. Thus, the incorporation of TiN nanoparticles into the composition of the PEO-coating improves significantly mechanical properties of the surface of magnesium alloys. This, in turn, makes it possible to expand the field of application of these materials in such industries as aviation, automotive, development of high-tech products and devices.

Earlier developed approaches to the formation of composite polymer-containing coatings by plasma electrolytic oxidation (PEO) using various low-molecular fractions of superdispersed polytetrafluoroethylene (SPTFE) have been summarized and a unique method for the formation of composite polymer-containing coatings at the surface of magnesium alloy MA8 has been suggested. The improvement in the corrosion and tribological behavior of the polymer-containing coating can be attributed to the morphology and insulating properties of surface layers and the solid lubrication effect of SPTFE particles. Such multifunctional coatings have high corrosion resistance ( R p = 3.0 × 10 7 Ω cm 2 ) and low friction coefficient (0.13) under dry wear conditions. The effect of dispersion and ξ -potential of the nanoparticles (ZrO 2 and SiO 2 ) used as an electrolyte component for PEO on the composition and properties of the coatings has been investigated. Improvement of the protective properties for coatings with the incorporated nanoparticles has been explained by the greater thickness of the protective layer, relatively low porosity and the presence of narrow non-through pores. The layer with zirconia has an impedance modulus measured at low frequency ( |Z| f →0Hz = 1.8 × 10 6 Ω cm 2 ) more than one order of magnitude higher than the PEO-coating formed in the electrolyte without nanoparticles ( |Z| f →0Hz = 5.4 × 10 4 Ω cm 2 ).

Direct laser deposition (DLD) technology was used to obtain magnesium (Mg) samples in this work. The morphology, composition, electrochemical and mechanical properties of the Mg specimens with and without protective layers were investigated using microhardness and scratch tests, SEM-EDX and XRD analysis, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), and immersion tests. The localized corrosion processes on the DLD Mg sample surface were studied using scanning vibrating electrode technique (SVET) and scanning ion-selective electrode technique (SIET). Plasma electrolytic oxidation (PEO) method was applied to modify the DLD Mg material intended to be used as bioresorbable implants for bone repair applications. Composite polymer-containing layers were designed to increase the corrosion resistance of the protected material. It was established that the use of additive technology for the formation of the material does not require correction of the electrical modes of PEO, developed for wrought magnesium alloys. The formed coatings possess high adhesive strength and sufficiently increase the protective properties of the DLD samples in a 3 wt% NaCl solution.

The features of the corrosion process in the artificial defect on the coating obtained by plasma electrolytic oxidation (PEO) method on an MA8 magnesium alloy were investigated using the localised electrochemical impedance spectroscopy (LEIS) technique. The analysis of the experimental data enabled us to suggest that the corrosion process in the defect zone develops predominantly at the magnesium/coating interface. The LEIS technique allows detecting the precision alterations result from corrosion process, which can not be found by optical image.