Search

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 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.

In this research the results of the formation of composite materials based on magnesium for the needs of implant surgery are discussed. The synthesis of porous magnesium with the inclusion of hydroxyapatite particles was preformed by means of a powder metallurgical mechanochemical process. The resulting samples were impregnated with bioactive additives such as shilajit. To protect against premature corrosion, the samples were coated with plasma electrolytic oxidation (PEO).

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°.

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.

Corrosion activity of the aircraft Al-Mg-Sc aluminium alloy has been studied using scanning electrochemical method. Microstructure analysis and phase composition have been determined in the present work. The reason of localized corrosion of the aluminium alloy has been established. This study promotes to understand the mechanism of the corrosion destruction of the material and to design technologies of its corrosion protection.

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.

Electrochemical behaviour of MA8 magnesium alloy in minimum essential medium (MEM) and 0.83 wt. % NaCl solution is compared using SVET, local pH measurements and hydrogen evolution tests. Corrosion products formed on the alloy surfaces are characterized using XRD and SEM-EDX analysis. Potential by-products of cells and bacteria activities increase the sample activity in MEM at the initial stage of material immersion. Hydrogen evolution rate is higher for samples in NaCl solution in comparison with MEM. Formation of partially protective magnesium-substituted hydroxyapatite stabilizes the local pH of MEM below 9.0 and does not allow to increase the pH during corrosion.

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.

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 paper studies microstructure, chemical composition and corrosion activity of the tungsten inert gas welded joint of the Al-Mg-Sc alloy. An intensive corrosion attack of the heat affected zone (HAZ) was found due to precipitation of secondary phases at recrystallized grain boundaries. The ccorrosion process initiated along the boundary of α-Al grains, where a high concentration of anodic (Mg2Si and Mg2Al3) and cathodic phases ((MnFe)Al6) was observed. Increased temperatures during welding led to coalescence of the anodic phases in HAZ. Additionally, HAZ was found to be enriched with hard intermetallic compounds (Mg2Si and (MnFe)Al6). This area had a higher microhardness (930 MPa) compared to base metal (BM, 895 MPa) and fusion zone (FZ, 810 MPa). The volume fraction of secondary phases was 26% in BM, 28% in FZ and 38% in HAZ. The average grain size increased in the following order: (9 ± 3) µm (BM) &lt, (16 ± 3) µm (HAZ) &lt, (21 ± 5) µm (FZ). A plasma electrolytic oxidation (PEO) coating of aluminum-based material was applied to protect the weld from oxidation. The PEO-coating provided a high corrosion protection in the aggressive Cl−-containing environment.

Magnesium has been considered as a new biodegradable material for orthopaedic applications because of its prominent properties including superior biocompatibility, biodegradability, and proper mechanical stiffness. For the direct production of custom biomedical implants, direct laser deposition (DLD) has been applied to fabricate bulk pure magnesium and its resultant properties were studied. Surface morphology, microstructure and mechanical properties of DLD specimen were investigated. The relative porosity of DLD specimen was equal to about 6 %. The microhardness and elasticity modulus of the DLD bulk magnesium were equal to (0.49 ± 0.09) GPa and (30 ± 4) GPa, respectively.

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.

Bioactive coatings on VT1-0 commercially pure titanium were formed by the plasma electrolytic oxidation (PEO). A study of the morphological features of coatings was carried out using scanning electron microscopy. A composition of formed coatings was investigated using energy-dispersive spectroscopy and X-ray diffractometry analysis. It was shown that PEO-coatings have calcium phosphate in their composition, which increases the bioactivity of the surface layer. Electrochemical properties of the samples were studied by potentiondynamic polarization and electrochemical impedance spectroscopy in different physiological media: simulated body fluid and minimum essential medium. The data of electrochemical studies indicate more than 15 times decrease in the corrosion current density for the sample with coating (5.0 &times, 10&minus, 9 A/cm2) as compared to the bare titanium (7.7 &times, 8 A/cm2). The formed PEO-layers have elastoplastic properties close to human bone (12&ndash, 30 GPa) and a lower friction coefficient in comparison with bare metal. The wettability of PEO-layers increased. The contact angle for formed coatings reduced by more than 60&deg, in comparison with bare metal (from 73&deg, for titanium to 8&deg, for PEO-coating). Such an increase in surface hydrophilicity contributes to the greater biocompatibility of the formed coating in comparison with commercially pure titanium. PEO can be prospective as a method for improving titanium surface bioactivity.

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.

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 way of self-healing coating formation at the surface of magnesium alloys by means of plasma electrolytic oxidation method (PEO) with subsequent filling of the obtained layer with inhibitor has been suggested. The electrochemical properties of such coatings have been described in details. The obtained experimental results indicate that the protective properties of the samples with inhibitor-containing coating were increased (IC = 8.6×10–8 A/cm2) in comparison with the samples without coating (5.3×10–5 A/cm2) and the base coating obtained by plasma electrolytic oxidation method (PEO) (3.4×10–7 A/cm2). The local scanning electrochemical methods of surface investigation, notably 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 by the solution containing 8-hydroxyquinoline, which inhibits the corrosion process, enables one to increase the protective properties of the composite coating in 30 times in the corrosion-active environment in comparison with the base PEO-coating and avert the intensive destruction of the material.

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 ).

In order to improve the corrosion resistance of magnesium alloys the ways of composite protective coating formation were developed by means of plasma electrolytic oxidation (PEO) as well as electrophoretic deposition methods. Electrochemical, corrosion, tribological, and morphological properties of the MAS magnesium alloy composite coatings were studied. The composite polymer-containing coating decrease the corrosion current density values by three orders of magnitude (Ic = 2.0 · 10−10 A/cm2), in comparison with the base PEO-layer. These polymer-containing layers enable one to expand the practical usage area of Mg alloys. The application of such coatings provides the increasing the bioactivity and regulate the corrosion rate of resorbable magnesium implants.

A greater corrosion stability of the MA8 (Mg-Mn-Се) alloy as compared to that of VMD10 (Mg-Zn-Zr-Y) magnesium alloy in the chloride-containing solution has been demonstrated using the scanning vibrating probe method (SVP) as well as the methods of optical microscopy, gravimetry and volumetry. It has been established that the crucial factor of the corrosion activity of the samples under study consists in the occurrence of the micro galvanic couples at the samples surface. MA8 alloy contains less amount of the secondary phases (cathodic parts) relative to VMD10. The corrosion rate of the samples with coatings formed by the plasma electrolytic oxidation (PEO) method and composite polymer-containing coatings at the surface of various magnesium alloys has been measured. It has established, that PEO-coating decrease the values of the corrosion rate in several times (more than one order of magnitude for MA8 and more than 2 times for VMD10) in comparison with bare alloys.

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.

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.

Magnesium can be used as a new biodegradable material for orthopaedic applications due to its outstanding properties including high biocompatibility, proper mechanical stiffness and biodegradability. Direct laser deposition (DLD) as a way of biomedical implant production has been used to make bulk pure Mg. Surface morphology, microstructure and mechanical properties of DLD sample have been studied. The relative porosity of DLD Mg sample has been determined.

Plasma Electrolytic Oxidation (PEO) has been widely studied for generating a protective oxide coating on a variety of metals such as titanium and aluminum alloys. It has however not been studied in great detail for nitinol alloy that is widely used in biomedical applications. In this article, we report the formation of a protective oxide coating on nitinol by the PEO process. The PEO-treated nitinol has been posttreated with Ultradisperse polytetrafluoroethylene (UPTFE) to study its effect on the morphology and protective properties of the coating. The electrochemical and mechanical properties of composition layers obtained have been investigated.