Search

Работа посвящена исследованию устойчивости к циклическим термическим воздействиям защитного покрытия, формируемого методом плазменного электролитического оксидирования и предназначаемого для защиты судовых теплообменных аппаратов от коррозии. Проведено исследование изменений, происходящих в фазовом составе, морфологической структуре, электрохимических и механических свойствах покрытия, подверженного термоциклированию. Ключевые слова: плазменное электролитическое оксидирование, ПЭО, рентгенофазовый анализ, РФА, электрохимия, температурные исследования, твердость

The production waste involvement in processing and recycling—one of the urgent tasks in the development of environmentally oriented and resource-saving technologies. In this work, two types of silicate-containing materials of plant (silicon dioxide from rice husk) and technogenic (calcium hydrosilicate) origin are studied as sorbents for removal of heterotrophic bacteria from water and as fillers for eco-friendly marine antifouling coatings. Characterizations (morphology, chemical composition, specific surface area, zeta-potential), bacterial adsorption performance and prepared samples efficiency in antifouling coating were investigated. The results showed that the sample of calcium hydrosilicate obtained from technogenic raw materials has a macroporous needle-like structure and characterized by high removal efficiency to Escherichia coli and Bacillus subtilis in 0,05 M NaCl. Sample of biogenic silicon dioxide characterized by globular micromorphology with high value of specific surface area. Incorporation of inorganic filler particles of biogenic and technogenic samples in the coating enhanced the paint hardness. Improved antifouling performance was shown for coatings with SiO2 from rice husk coupled with bacterial antifouling extract during 9 months of field test.

The plasma electrolytic oxidation (PEO) process was used to form an oxide layer on an Al5754 aluminum alloy for subsequent application of organic coating. The effect of the oxidation time on the morphology and anticorrosion properties of PEO-coatings was investigated. The oxide layer possess low apparent porosity and provides high adhesion to the paint. The resulting composite coating (CC) is characterized by high barrier properties in chloride solution.

Plasma electrolytic oxidation (PEO) was used to form a protective layer on 5754 and 2024 aluminum alloys to improve the corrosion properties of the processed materials. The protective performances of the obtained coatings were studied by a combination of electrochemical methods and salt spray test. The absence of pitting corrosion after a 7-day test for the entire series of PEO-layers on aluminum alloys 5754 and 2024 was confirmed by scanning electron microscopy (SEM). Also, microcracks were detected only in the SEM-image for the most porous and thin PEO-coating formed on aluminum alloy 2024 at duty cycle = 0.06 and 30 min.

The paper presents the results of a study of the protective properties of composite coatings obtained on AMg3 aluminum alloy by plasma electrolytic oxidation (PEO) and subsequent modification of formed oxide layer with superdispersed polytetrafluoroethylene (SPTFE) from a suspension based on isopropyl alcohol. The incorporation of fluoropolymer decreased the porosity of base PEO-coating more than one order of magnitude. Formed composite layers increased wearproof of the samples by more than two orders of magnitude in comparison with PEO-coating. Additionally, polymer-containing coatings has higher adhesion compared to substrate. Formed composite layers possess superhydrophobic properties: contact angle attains 155°.

The results of studying the morphology, porous structure, and corrosion and diffusion properties of boehmite-containing calcium phosphate coatings formed by microarc oxidation on titanium substrates are presented. Boehmite nanoparticles obtained as a result of the AlN hydrolysis were deposited on the surface of microarc coatings with a developed relief. With an increase in the duration of the preliminary ultrasonic treatment (UST) of the AlN suspension in the interval of 20–60 min, the size of agglomerates of boehmite nanoparticles on the coating surface is decreased from 200 to 40 μm. The surface porosity of the modified coatings and the area occupied by boehmite particles are decreased from 36 to 33% and from 27 to 10%, respectively. Agglomerates with boehmite nanoparticles after 60 min of UST of an AlN powder suspension are distributed in the coating more uniformly than after 20 min of treatment. When the duration of UST of the initial suspensions is increased, the effective diffusion coefficients of the model biological fluid in porous coatings is decreased from 7.98 × 10–11 to 7.25 × 10–11 m2/s. Modification of calcium phosphate coatings with boehmite nanoparticles by varying the duration of UST of AlN powder increases the corrosion resistance of the surface layers.

This paper presents the results of an evaluation of anti-icing properties of samples obtained by plasma electrolytic oxidation (PEO) with a subsequent application of superdispersed polytetrafluoroethylene (SPTFE) and polyvinylidenefluoride (PVDF). A combined treatment of the samples with SPTFE and PVDF is also presented. It is revealed that impregnation of a PEO layer with fluoropolymer materials leads to a significant increase in surface relief uniformity. Combined PVDF–SPFTE layers with a ratio of PVDF to SPTFE of 1:4 reveal the best electrochemical characteristics, hydrophobicity and icephobic properties among all of the studied samples. It is shown that the decrease in corrosion current density Ic for PVDF–SPFTE coatings is higher by more than five orders of magnitude in comparison with uncoated aluminum alloy. The contact angle for PVDF–SPFTE coatings attain 160.5°, which allows us to classify the coating as superhydrophobic with promising anti-icing performance. A treatment of a PEO layer with PVDF–SPFTE leads to a decrease in ice adhesion strength by 22.1 times compared to an untreated PEO coating.

In this paper, the morphological features of textures with non-uniform wettability created using femtosecond laser ablation of polytetrafluoroethylene substrates have been studied. Covering the surface of polytetrafluoroethylene with microcraters in accordance with a proper design a texture in the form of periodically located microcollets could be created. The period of the location of the columns is the same over the entire surface and is selected in the range from 15 to 100 microns. In the case when the period lies within 30–100 µm, the diameter of the bars is ~ 20 µm. If in the range of 15–20 µm, then this diameter decreases accordingly to ~ 10 µm. Depending on the pulse energy, the height of the pillars could be smoothly changed from 0 to 60 μm. However, to create a superhydrophobic concentrator, textures with the greatest depth were used so that the height of the columns does not limit the stability of the superhydrophobic state by the sagging mechanism. It was established that on the surface of each pillar during the process of laser ablation, a relief with a two-modal roughness in the form of short drop-shaped projections of the material covered with spherical globules is additionally formed. Thus, in one stage of laser micromachining, it is possible to create a surface with a three-modal roughness – microcolumns, drop-shaped projections and spherical globules. The process of droplet evaporation is represented by two main modes of constant contact angle and constant contact diameter, when the latter ceases to decrease and remains constant until the complete evaporation of the drop. As a result, a precipitate of the substance dissolved in a drop is formed on the substrate. It has been established that in the interval 0

Biodegradable materials are currently attracting the attention of scientists as materials for implants in reconstructive medicine. At the same time, ceramics based on calcium silicates are promising materials for bone recovery, because Ca2+ and Si2+ ions are necessary for the mineralization process, and they take an active part in the formation of apatite. In the presented research, the protective silicate biocoatings on a Mg0.8Ca alloy were formed by means of the micro-arc oxidation method, and the study of their morphology, structure, phase composition, corrosion, and biological properties was carried out. Elongated crystals and pores were uniformly distributed over the surface of the coatings. The coated samples exhibited remarkable anti-corrosion properties in comparison with bare magnesium alloy because their corrosion current decreased 10 times, and their corrosion resistance increased almost 100 times. The coatings did not significantly affect the viability of the cells, even without the additional dilution of the extract, and were non-toxic according to ISO 10993-5: 2009. In this case, there was a significant difference in toxicity of the pure Mg0.8Ca alloy and the coated samples. Thus, the results demonstrated that the applied coatings significantly reduced the toxicity of the alloy.

The composite calcium-phosphate coating on MA8 Mg alloy consisting of the inorganic porous basis sealed with polymer is suggested. To control the alloy resorption kinetics, the coating obtained by plasma electrolytic oxidation is modified with superdispersed polytetrafluoroethylene using electrophoretic deposition (EPD). Protective properties and morphology evolution as a result of surface treatment and corrosion propagation are examined by EIS, PDP, hydrogen evolution tests, SEM, EDX and XRD analysis. The obtained coatings are investigated at mechanistic level using SVET and local pH measurements. EPD composite coating decreases electrochemical activity of the sample in minimum essential medium and ensures the material biocompatibility.

The plasma electrolytic oxidation is an innovative method for the surface treatment of titanium and its alloys. This review provides an overview of the historical development of the process and summarizes the current state of the art. The chemical as well as the electro- and plasma-chemical basics of the layer forming mechanisms, which comprises the substrate/electrolyte interface before discharge initiation and the different types and stages of plasma electrolytic discharge phenomena are explained within the context of titanium-based materials. How these phenomena can be influenced by the use of suitable electrolytes and controlled by the electrical regime is described. Subsequently, the microstructures and composition of the layers are described in detail, and the properties for specific applications are then discussed. The resistance of a PEO coating to corrosive environments, tribological factors, and alternating mechanical stress is viewed critically, and the extensive functional properties such as physiological compatibility, photocatalytic activity, and decorative properties are revealed. Finally, examples of various practical applications in the medical engineering, aviation, automotive, and environmental technology fields, as well as other branches of industry, are presented., M. Aliofkhazraei acknowledges comments received from Prof. A. Yerokhin during intial steps of preparation of this review paper. D.D. Macdonald gratefully acknowledges the support of the FUTURE (Fundamental Understanding of Transport Under Reactor Extremes), an Energy Frontier Research Center funded by the U.S. Department of En- ergy (DOE), Office of Science, Basic Energy Sciences (BES). E. Matykina would like to thank the support of the RTI2018-096391-B-C33 (MCIU/ AEI/FEDER, UE) and S2018/NMT-4411 (Regional Government of Madrid and EU Structural and Social Funds). S.V. Gnedenkov ac- knowledges the support of the Russian Science Foundation (No. 20-13- 00130).

A comparative analysis of the structure, properties and the corrosion behavior of the micro-arc coatings based on Sr-substituted hydroxyapatite (Sr-HA) and Sr-substituted tricalcium phosphate (Sr-TCP) deposited on Mg0.8Ca alloy substrates was performed. The current density during the formation of the Sr-HA coatings was higher than that for the Sr-TCP coatings. As a result, the Sr-HA coatings were thicker and had a greater surface roughness Ra than the Sr-TCP coatings. In addition, pore sizes of the Sr-HA were almost two times larger. The ratio (Ca + Sr + Mg)/P were equal 1.64 and 1.47 for Sr-HA and Sr-TCP coatings, respectively. Thus, it can be assumed that the composition of Sr-HA and Sr-TCP coatings was predominantly presented by (Sr,Mg)-substituted hydroxyapatite and (Sr,Mg)-substituted tricalcium phosphate. However, the average content of Sr was approximately the same for both types of the coatings and was equal to 1.8 at.%. The Sr-HA coatings were less soluble and had higher corrosion resistance than the Sr-TCP coatings. Cytotoxic tests in vitro demonstrated a higher cell viability after cultivation with extracts of the Sr-HA coatings.

The difference of the protective properties of the corrosion film formed on the MA8 Mg alloy in the mammalian cell culture medium (MEM) and 0.83 wt. % NaCl solution is established using OCP, PDP and EIS tests. The impedance modulus in the frequency range from 105 Hz down to 10−1 Hz for the sample immersed in MEM is higher than that for the sample immersed in NaCl solution. Ca and P rich deposits are formed in the corrosion layer on the Mg alloy in MEM. The model of the corrosion mechanism for MA8 Mg alloy in the MEM is proposed.

Plasma electrolytic oxidation (PEO) of 5754 aluminum alloy in a tartrate electrolyte was carried out to form a base layer. Composite fluoropolymer coatings were obtained on the base layers in two ways allowing the formation of two different types of morphological structure: a continuous polymer film and a multimodal islet relief. The resulted coatings exhibit substantially different wettability along with high level of barrier properties.

Plasma electrolytic oxidation (PEO) of aluminum alloy 5754 was carried out in a multicomponent electrolyte variating the concentration of sodium silicate. The research has allowed to establish the characteristic features of the plasma electrolytic oxidation process, and also morphological structure of the formed oxide layers. It is established that the applied electrolytic systems can significantly increase the thickness of the formed layers (up to 152 μm), and control their porosity, bringing it up to 30 %.

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.

Comparative corrosion tests are performed of doped stainless steels: conventional stainless steel 12Kh18N10T and new high-tension austenitic steel 05Kh22AG15N8M2F with 0.47 wt % N with its flow limit being 2.5 times higher than that of the 12Kh18N10T steel. The resistance of steels to electrochemical corrosion in 3% NaCl solution is studied and field marine and atmospheric corrosion tests are performed. It is shown that the 05Kh22AG15N8M2F steel is characterized by higher corrosion stability than the 12Kh18N10T steel in both laboratory and field tests.

A study was made into the morphology, composition, and electrochemical and mechanical properties of protective composite coatings on various aluminum alloys, including those doped with Sc, Cu, and Ni. It was established that protective coatings significantly increase the corrosion resistance of the alloys in a 3% NaCl solution. Composite coatings produced by triple dip coating in an superdispersed polytetrafluoroethylene suspension have unique corrosion-resistance properties, reducing the corrosion current density for all the protected alloys to 3.1 × 10–11–4.0 × 10–12 A/cm2, which is more than three orders of magnitude lower than that for coatings formed by plasma electrolytic oxidation and five orders of magnitude lower than that for alloys without coating.

Morphology, composition, and barrier properties of superhydrophobic (SHP) coatings on the surface of AMg3 aluminum alloy pretreated by plasma electrolytic oxidation (PEO) have been investigated. Results of the study of hydrophobic layers on aluminum alloy, which underwent plasma electrolytic oxidation (PEO) and additional treatment 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. Coatings formed by deposition of dispersion of the hydrophobic agent containing SiO 2 nanoparticles on the surface of the PEO-layer are characterized by high contact angles and inhibitive properties. The formed composite layers were found to be characterized with hydrophobicity (contact angle higher than 157°) and high barrier properties (the impedance modulus, | Z | f = 0.01 Hz , ranges from 9.2 × 10 9 to 1.1 × 10 11 Ω cm 2 depending on the treatment procedure).

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.

Recent results of plasma electrolytic oxidation modification of the surfaces of Ti as well as NiTi alloy obtained by a joint effort of Institute of Chemistry FEB RAS, Institute of Strength Physics and Materials Science SB RAS, and Russian Ilizarov Scientific Center for Restorative Traumatology and Orthopedics are demonstrated in comparison with the literature ones. Conditions of coating synthesis determine their functional designation. It is presented that purposeful selection of the electrolyte composition used for coating formation has allowed to obtain layers containing Ca and P, whose bioactivity is confirmed both in vitro and in vivo. Prospects for the application of the plasma electrolytic oxidation method for the formation of the composite bioinert coatings at the titanium nickelide surface improving its morphological structure and electrochemical properties and significantly reducing the quantity of nickel ions releasing into the organism are demonstrated.

The high electrochemical activity of the aircraft 1579 aluminium alloy with a welded joint and the necessity of the coating formation to protect this material against corrosion as well as to increase the stability of the weld interface in the corrosive medium has been previously established. In this work, two suggested methods of protective coating formation based on plasma electrolytic oxidation (PEO) in tartrate-fluoride electrolyte significantly increased the protective properties of the welded joint area of the 1579 Al alloy. The electrochemical properties of the formed surface layers have been investigated using SVET (scanning vibrating electrode technique) and SIET (scanning ion-selective electrode technique), EIS (electrochemical impedance spectroscopy), OCP (open circuit potential), and PDP (potentiodynamic polarization) in 0.5 M NaCl. The less expressed character of the local electrochemical processes on the welded 1579 Al alloy with the composite coating in comparison with the base PEO-layer has been established. Polymer-containing coatings obtained using superdispersed polytetrafluoroethylene (SPTFE) treatment are characterized by the best possible protective properties and prevent the material from corrosion destruction. Single SPTFE treatment enables one to increase PEO-layer protection by 5.5 times. The results of this study indicate that SVET and SIET are promising to characterize and to compare corrosion behaviour of coated and uncoated samples with a welded joint in chloride-containing media.

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.

The characterization of the microstructure, morphology, topography, composition, and physical and chemical properties of the coatings containing β-tricalcium phosphate (β-TCP) particles deposited by the micro-arc oxidation (MAO) method on biodegradable Mg-0.8Ca alloy has been performed. The electrolyte for the MAO process included the following components: Na2HPO4·12H2O, NaOH, NaF, and β-Ca3(PO4)2 (β-TCP). The coating morphology, microstructure, and compositions have been studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). With increasing of the MAO voltage from 350 to 500 V, the coating thickness and surface average roughness of the coatings increased linearly from 6 to 150 µm and from 2 to 8 µm, respectively. The coating deposited at 350 V had more homogeneous porous morphology with numerous pores similar by sizes (2–3 µm) than the coatings formed at 450–500 V. The β-TCP isometric particles were included in the coating surface. The XRD recognized the amorphous-crystalline structure in the coatings with incorporation of the following phases: β-TCP, α-TCP, MgO (periclase) and hydroxyapatite (HA). The corrosion experiments showed that the biodegradation rate of the Mg-0.8Ca alloy coated by calcium phosphates is almost 10 times less than that of uncoated alloy.

The influence of the boehmite nanoparticles on the properties of the calcium phosphate biocoatings obtained by the micro-arc oxidation (MAO) was investigated. Boehmite nanoparticles were precipitated on the porous CaP coatings using hydrolysis reaction carried out in suspension with distilled water and AlN powder. It was shown that boehmite nanoparticles were detected on the surface of CaP coatings and inside the pores of coating surface. It was established that coatings modified with boehmite nanoparticles have high corrosion resistance properties.

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).

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.

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).

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.

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.

The method of formation of bioactive calcium-phosphate coating on medical titanium alloy Ti-6Al-4V (3.5-5.3% V; 5.3-6.8% Al; balance -Ti) by plasma electrolytic oxidation (PEO) has been developed. Evaluation of osteogenerating properties of the coating at fractures of the shaft of the femur on Wistar line laboratory rats has been performed. It has been established that the calcium-phosphate PEO coating accelerates osteogenesis and promotes the formation of a pronounced periosteal callus in the fracture area. The presence of calcium phosphates in the PEO coating surface layer significantly accelerates the growth of bone tissue on the titanium surface.

The results of the study aimed at assessing the effect of the duty cycle (D) during plasma electrolytic oxidation (PEO) on morphology, chemical composition, and barrier properties of the coatings produced on 5754 aluminum alloy are presented. It is shown that increasing the duty cycle of a microsecond current pulses leads to increased thickness and decreased porosity along with improved electrochemical parameters.

Bioactive calcium-phosphate coating on Ti–6Al–4V titanium alloy was formed by plasma electrolytic oxidation (PEO). The osteogenerating properties of the obtained coating were assessed in vivo at fractures of the shaft of the femur of laboratory rats. The obtained PEO-coating accelerates osteogenesis and promotes the formation of a pronounced periosteal callus in the fracture area. The bone tissue growth on the surface of the implant was significantly accelerated by the presence of calcium phosphates in the chemical composition of the PEO-coating.

We present results of the study aimed at assessing the effect of duty cycle (D) during plasma electrolytic oxidation (PEO) on protective properties of the coatings produced on 5754 aluminum alloy. It is shown that increasing the duty cycle of a microsecond current pulses leads to increased hardness and reduced abrasive wear of the PEO-layers, improving mechanical properties. The obtained data allowed confirming, that increasing the amount of energy consumed for coating growth leads to the formation of thicker PEO-layers with improved tribological properties. The effect of duty cycle during plasma electrolytic oxidation on protective properties of the produced coatings was assessed.

Multifunctional corrosion resistant and bioactive coatings containing hydroxyapatite Ca10(PO4)6(OH)2 and magnesium oxide MgO were obtained on Mg–Mn–Ce alloy by plasma electrolytic oxidation. The phase and elemental composition, morphology and anticorrosion properties of the coatings were investigated. The PEO layers were post-treated using Forum® superdispersed polytetrafluoroethylene powder, which caused a considerable reduction of the magnesium alloy corrosion rate (>4 orders of magnitude). In particular, the polarisation resistance has increased, as a result of such duplex treatment, by five orders of magnitude. The composite coatings are considered promising to induce bioactivity and control corrosion degradation of resorbable Mg implants.

Superhydrophobic layers were prepared by means of nanoparticle dispersions deposition on PEO (plasma electrolytic oxidation)-pretreated metal/alloy (titanium, low-carbon steel, and magnesium) substrates. The contact angles on the surface of the fabricated coatings were higher than 160°. The comprehensive analysis of the data obtained by electrochemical method provides the possibility to study variations in the surface conditions due to the electrochemical reaction associated with the corrosion process. It was found that the combined effect of PEO treatment and textured hydrophobic layer deposition results in inhibition of the corrosion reactions and ensures the anticorrosive behavior of the coatings. As follows from the electrochemical data analysis, the corrosion protection for nanocomposite superhydrophobic coatings formed on the PEO-layer is provided by small area of real contact with the electrolyte solution and higher ohmic barrier for corrosion reactions. In case of superhydrophobic layers, the mass transfer of electrolyte solution through the coating to the metal surface is substantially hindered.

The 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. A unique method for the formation of a composite polymer-containing coating 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 solid lubrication effect of SPTFE particles. Such multifunctional coatings have high corrosion resistance (Rp = 3.0 × 107 Ω cm2) and low friction coefficient (0.04) under dry wear conditions.

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.