Igor E. Vyaliy

Plasma Electrolytic Oxidation Coatings on Titanium Formed with Microsecond Current Pulses

The effects of shape and duration of the current pulses on the physico-chemical properties of the oxide layers on titanium formed by plasma electrolytic oxidation were examined. It was shown that in the investigated conditions transistor power source possess an advantage in comparison with thyristor one. Electrochemical properties of the heterooxide structures were examined by electrochemical impedance spectroscopy and potentiodynamic polarization methods.

Effect of polarizing signal duty cycle on the composition, morphology, and protective properties of PEO coatings on AMg3 aluminum alloy

This paper presents a study aimed at assessing the effect of polarizing signal duty cycle D in the plasma electrolytic oxidation (PEO) process on the composition, morphology, and protective properties of coatings produced on AMg3 aluminum alloy in a tartrate-containing electrolyte. It is shown that increasing the duty cycle of a short-pulse (τ = 5 μs) polarizing signal leads to a decrease in the porosity of the growing PEO layers. This, in turn, improves the protective properties and surface strength of the alloy. The pulse duty cycle influences the chemical composition and thickness of the growing oxide coatings.

Protective Properties of the Nanocomposite Coatings on Mg Alloy

Nanocomposite coatings were obtained by aggregation of nanoparticles from dispersion in decane on the surface of oxide coatings. Oxide coatings on magnesium alloy were formed by plasma electrolytic oxidation in silicate containing electrolyte in bipolar mode. Electrochemical properties and stability of nanocomposite coatings under conditions of prolonged exposure to chloride containing environment were studied by means of electrochemical impedance spectroscopy, potentiodynamic polarization and measurements of contact angles. The coatings possess superhydrophobic properties with the contact angle of 166o ± 3o and the rolling angle of 5o ± 3o. It was found that these nanocomposite coatings reduce the corrosion current of magnesium alloy by more than three orders of magnitude. High stability during immersion in aggressive media is due to a small contact area of the coatings with electrolyte and high adhesion of the hydrophobic agent molecules with the coating.

Morphological Features and Electrochemical Properties of the Hydrophobized Sealed PEO-Coatings on Al Alloy

The developed methods of formation and results of the study of the hydrophobic layers on aluminum alloy, previously subjected to plasma electrolytic oxidation (PEO), boiling in bidistilled water, and additional treatment (either in ethanol solution or under UV-radiation in the presence of ozone plasma) with subsequent deposition of the hydrophobic agent (methoxy-{3-[(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoroctyl) oxy] propyl}-silane solution in decane) have been described. It was found, that the formed composite layers possess hydrophobicity (contact angle higher 155o) and high anticorrosion properties (the impedance modulus (|Z|f = 0.01 Hz) ranges from 1.5·108 to 1.7·108 Оhm·cm2 depending on treatment procedure).

Duty Cycle of the Polarizing Signal Influence on Morphology and Properties of the PEO-Coating on Aluminium Alloy

Influence of the polarizing signal parameter used during plasma electrolytic oxidation (PEO) on the composition, morphology and properties of protective coatings formed on aluminum alloy in tartrate-containing electrolyte has been presented. It was established, that using of the short-pulse bipolar polarizing signal (τ=5 μs) facilitates the reduction of porosity and roughness of the formed PEO-layers. This, in turn, increases wearproof and protective corrosion characteristics of the treated alloy surface. Increasing the duty cycle (D) affects on the chemical composition and the thickness of the obtained coatings.

Corrosion of the Welded Aluminium Alloy in 0.5 M NaCl Solution. Part 1: Specificity of Development

This work consists of two parts. In the first part, the kinetics and mechanism of corrosion on the surface of the welded joint area of the aircraft 1579 aluminium alloy have been studied using SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique) in 0.5 M NaCl. The results have revealed the corrosion process development within the weld interface due to the presence of microdefects in the morphological structure. Features of the 1579 Al alloy corrosion have also been investigated through immersion experiments, quantitative analysis of dissolved alloying elements by means of atomic absorption spectroscopy, and corrosion products characterization using XRD (X-ray diffraction) analysis. The presence of Mg as an alloying element in the 1579 Al alloy sufficiently increases the bulk pH values as a result of the intensive dissolution of Mg. These factors accelerate the corrosion activity of the studied material in the 0.5 M NaCl solution. Corrosion evolution analysis of the 1579 Al alloy sample showed the importance of the coating formation to protect this alloy against corrosion and to increase the stability of this system in the corrosive media.

Electrochemical and Mechanical Properties of the PVDF/PEO-Coatings on Magnesium Alloy

The paper presents the results of the study of electrochemical and mechanical properties of PVDF/PEO-coatings formed on magnesium alloy MA8 by plasma electrolytic oxidation (PEO) and subsequent application of polyvinylidene fluoride (PVDF) on the PEO-layer. The oxide coatings were formed using a 300 Hz bipolar signal with duty cycle (D) 0.50. The analysis of electrochemical data has showed a decrease of corrosion currents by 3 orders of magnitude (down to 6.0·10-9 А·сm-2) and an increase of the polarization resistance by 3 orders of magnitude (up to 5.3·106 Оhm·сm2) for the coatings formed by triple dipping (x3) of the PEO-layers into PVDF solution. Evaluation of the tribological properties of the (x3) PVDF/PEO-coatings has showed a significant increase of the wear resistance (the number of abrasion cycles resulting in complete destruction of the coating increased in 25 times) as compared to the base PEO-layer.

Evaluation of Electrochemical Properties of the PEO-Coatings Treated with Hydrophobic Agent Solution on Aluminium Alloy

The developed methods of formation and results of the study of the hydrophobic layers on aluminum alloy, previously subjected to plasma electrolytic oxidation (PEO) and additional treatment (either in ethanol solution or under UV-radiation in the presence of ozone plasma) with subsequent deposition of the hydrophobic agent (methoxy-{3-[(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluoroctyl) oxy] propyl}-silane solution in decane) have been described. It was found, that the formed composite layers possess a hydrophobicity (contact angle higher 157o) and high anticorrosion properties (the impedance modulus, |Z|f=0.01Hz, ranges from 9.2·109 to 4.0·1010 Оhm·cm2 depending on the treatment procedure).

Formation and Properties of the PVDF/PEO-Coatings on Commercially Pure Titanium

Plasma electrolytic oxidation (PEO) of commercially pure titanium VT1-0 was performed in phosphate electrolyte. High-frequency 200 kHz bipolar signal at a duty cycle D=0.1 was used to form the oxide coatings. Polymer-containing anticorrosion coatings were formed by applying polyvinylidene fluoride (PVDF) on the base PEO-coating. The results of electrochemical tests have showed a decrease of corrosion current density by 2 orders of magnitude (down to 1.5∙10-10 А∙сm-2) and the corresponding increase of the polarization resistance (up to 1.9∙108 Оhm∙сm2) in comparison with the metallic substrate.