PEO Treatment Research Articles

Production of Porous ZrO2–TiO2 Ceramic Coatings on the Biomedical Ti-6Al-4V Alloy via AC PEO Treatment and Their Effects on the Corrosion Behavior in 0.9% NaCl

Production of Porous ZrO2–TiO2 Ceramic Coatings on the Biomedical Ti-6Al-4V Alloy via AC PEO Treatment and Their Effects on the Corrosion Behavior in 0.9% NaCl

Influence of non-valve metal phase on growth behavior and performance of PEO coating on Mg–Zn–Mn alloys with high Mn content

The influence of pure metal phases (precipitation or reinforcement phases) on the PEO discharge and coating growth in Mg alloys remains underexplored. This study investigated the effects of the α-Mn phase on voltage evolution, coating morphology, phase composition, and corrosion resistance by subjecting Mg–4Zn-xMn (x = 0, 0.6, 1.2, 2.4 wt%) alloys to PEO treatment in alkaline silicate-based electrolyte. Results indicate that the presence of α-Mn does not prevent spark discharge. However, an increase in α-Mn content leads to a downward shift in the voltage-time curve. The α-Mn phase significantly slows down the voltage ascent rate and prolongs the duration of Stages I to III of PEO process. Electrochemical oxidation of the surrounding Mg matrix by the α-Mn phase induces the formation of pits and porous local morphologies, exacerbating coating unevenness. With the increasing in Mn content, the thickness and porosity of PEO coatings gradually decrease for the same treatment time. The coated Mg–4Zn-1.2Mn alloy exhibits the highest corrosion resistance. The differences in oxidizability between the α-Mn phase and the Mg matrix, as well as the stability and dielectric properties of the oxide products may be the underlying reasons for these effects. Despite Mn oxides' instability under alkaline conditions at high potentials, reaction products with the electrolyte offset this drawback. This study enhances understanding of pure metal phases' influence on Mg alloy PEO and contributes to research on PEO processes for Mg-based materials containing pure metal phases.

The Effect of Self-Healing Microcapsules in Corrosion Testing on Magnesium AZ31 Alloy and Fibre Metal Laminates

Fibre metal laminates (FMLs) are the most interesting composite materials of the past decade. They possess the properties of both polymer composites and metallic alloys. However, there is a problem with corrosion when the outer layers are made of aluminium or magnesium. The electrochemical changes that occur during the corrosion process and the mechanisms associated with the corrosion phenomenon are still being investigated. Recently, self-healing phenomena have emerged as a useful approach to prevent corrosion. However, there is limited research on the combination of FMLs and self-healing layers. Therefore, the main purpose of this article is to evaluate the self-healing ability of a magnesium/PEO layer based on microcapsules in a corrosion environment. It was observed that the corrosion mechanism in magnesium alloys is very complex. However, the use of a barrier layer with PEO treatment and microcapsules yielded positive anti-corrosion results. The FML samples were subjected to a 6-week corrosion test, and the addition of microcapsules to the layers showed positive results. In contrast, the samples without microcapsules exhibited intergranular corrosion. In the future, comprehensive tests using self-healing microcapsules in FMLs could greatly enhance their anti-corrosion properties and improve the integrity of the structure.

Exploiting the effect of PEO parameters on the surface of AISI 1020 low-carbon steel treated in a TaOH-rich electrolyte

This study used PEO treatment and a TaOH-rich electrolyte to coat AISI 1020 low-carbon steel to enhance its anti-corrosion and wear properties, targeting its usage as a medical device. The effect of time, duty cycle, frequency, and Ta(OH)5 concentration on the chemical and phase composition, topography, wettability, and roughness of the obtained coatings were addressed. The results indicated that the Fe-based oxide coatings had a rough and super-hydrophilic surface. The phase composition of the coatings was formed mainly of Ta2O5, hematite (Fe2O3), and a minor amount of rust (Fe(OH)2), with the chemical analyses also indicating the presence of some absorbed molecules. Once the best PEO parameters were established (200 V, 5 min, 60 %, 1000 Hz, and 40 g/L Ta(OH)5), the previous mechanical, corrosion, and wear tests evidenced the positive effect of the chemical species deposited in the surface when compared to the substrate. In this way, PEO treatment applied on AISI 1020 low-carbon steel in a TaOH-rich electrolyte can be an adequate alternative to produce low-cost materials for medical devices, especially as a potential substitute for stainless steel and titanium-based alloys in surgical instruments.

Formation process and characteristics of an amorphous SiO2 ceramic coating on 6061 aluminum alloy by plasma electrolytic oxidation in organosilicon electrolyte

An amorphous silica ceramic coating with thicknesses exceeding 100 μm (adjustable thickness) was prepared on 6061 aluminum alloy by plasma electrolytic oxidation in organosilicon electrolyte. To investigate its formation process and structural characteristics, the digital microscope system, SEM, X-ray diffractometer and microhardness tester were used to characterize morphology, structure and hardness at different voltages and times. The results show that it thickens rapidly after the voltage is raised to 480–500 V, and its surface begins to roughen and the micropores appear to enlarge. In organosilicon electrolyte, unlike conventional electrolytes, the coarse Al–Fe–Si second phase particles in the matrix do not negatively affect the PEO treatment. The produced coatings increase the surface hardness of 6061 aluminum alloy by more than 6 times and are stable in common acid solutions such as HCl and HNO3. Furthermore, the energy consumption rate of PEO treatment can be significantly reduced to 0.24–0.31 kJ cm−2 μm−1. The potentiodynamic polarization curves measured in 1 mol L−1 HCl solution show that the ceramic coating can reduce the corrosion current density of 6061 aluminum alloy from 3.74 × 10−2 A cm−2 to 2.24 × 10−6 A cm−2. And its corrosion resistance can be further improved by adding a 2nd low-voltage PEO treatment.

Role of anodic precursor layer thickness on PEO coatings: Energy consumption and long-term corrosion performance

PEO coatings with different thickness of anodic precursor films (5, 10, 20 and 40 μm) were successfully developed on AA2024 with the aim of determining how the thickness of anodic films affects the development of PEO film, structural growth, surface morphology, phase composition, and associated long term corrosion resistance properties. Compared to direct PEO treatment, reductions in the energy consumption (kW.h.m2.μm−1) of 71 %, 41 %, and 17 % are obtained at similar PEO processing conditions for the pre-anodized specimens of 40 μm, 20 μm, and 10 μm film thickness, respectively, while the time to current drop for above specimens reduced to 86.2 %, 63.3 % and 33.3 %, associated to the early formation of the “soft sparking” regime. The results suggest the effectiveness of pre-anodization on the PEO coatings for minimum energy consumption, developed explicitly on 20 and 40 μm anodic film, whereas overall PEO on anodic precursors exhibited a thicker oxide layer, homogenous pore size distribution, and long-term corrosion protection comparable to the original PEO layer. Based on the energy consumption and corrosion resistance of PEO on anodic precursor, a model of PEO coating growth is proposed, which can be considered a thorough insight towards highly developing energy-efficient PEO for practical applications.

Microstructure and corrosion resistance of Ti and Ti-40Nb alloy modified by plasma electrolytic oxidation in tricalcium phosphate suspension

Commercially available, modification of the surface of the modification of the surface of the Ti CP and Ti-40Nb alloys by plasma electrolytic oxidation in a tricalcium phosphate suspension with silver nitrate has been reported. The determined characteristics of the obtained coatings were related to microstructural studies, chemical composition, wettability, and corrosion tests. The proposed treatment ensured the effective incorporation of bioactive compounds into the oxide coatings. Electrochemical corrosion tests showed superior corrosion resistance for both substrates, with higher corrosion resistance obtained for Ti-40Nb samples in baths containing silver nitrate. The presented research highlighted the potential application of PEO treatment of Ti alloys for the purpose of hard tissue implants.

Plasma Electrolytic Oxidation for Dental Implant Surface Treatment.

50 IRIS dental implants (Scientific Production Company LICOSTOM, Russia), 10-mm long and 4 mm in diameter, were manufactured from the VT1-0 alloy. The implant surface was treated by two PEO methods: 1) in the aqueous solution of alkaline electrolyte without any additional modifiers (PEO-Ti); 2) in the aqueous solution of orthophosphoric acid-based electrolyte containing calcium carbonate (PEO-Ca). Implants made of VT1-0 alloy after milling and without additional treatment served as control samples. The implant surfaces were studied by electron microscopy and energy dispersive X-ray spectrometry. Some of the implants were installed in sheep, samples were obtained at 2, 4, and 8 weeks and studied by microcomputer tomography. Regardless of the electrolyte composition, a highly developed porous surface was formed in the samples with PEO-modified surfaces. The surface of the PEO-Ti samples in a simple unmodified electrolyte was characterized by a large number of open pores with a wide range of size distribution from 200 nm to 3 μm. The pore size distribution was of a monomodal character, with a maximum near 0.23 μm. The PEO samples in the Ca-containing electrolyte had pores also in a wide range from ~80 nm to ~7 μm. The pore distribution, in contrast to PEO-Ti, was bimodal in nature, with the main maximum in the region of 1.05 μm and the concomitant maximum near 2.45 μm.The obtained surfaces of both types (PEO with Ca and Ti) possessed high purity and optimal microroughness for osseointegration. Both types of PEO treatment (PEO with Ca and Ti) have demonstrated a similar osseointegrative potential, nevertheless, the surface of the PEO-Ca showed a better contact with the implant surface (49.8%) than PEO-Ti (42.4%) obviously due to the presence of calcium in its composition. The PEO-formed implant surfaces demonstrate high osseointegrative properties after any variants of treatment and show the potential for application in osteoporosis.

Perovskite interface defect passivation with poly(ethylene oxide) for improving power conversion efficiency of the inverted solar cells.

Inverted perovskite solar cells (PSCs) attract researchers' attention for their potential application due to the low-temperature fabrication, negligible hysteresis and compatibility with multi-junction cells. However, the low-temperature fabricated perovskite films containing excessive undesired defects are not benefit for improving the performance of the inverted PSCs. In this work, we used a simple and effective passivation strategy that Poly(ethylene oxide) (PEO) polymer as an antisolvent additive to modify the perovskite films. The experiments and simulations have shown that the PEO polymer can effectively passivate the interface defects of the perovskite films. The defect passivation by PEO polymers suppressed non-radiative recombination, resulting in an increase in power conversion efficiency (PCE) of the inverted devices from 16.07% to 19.35%. In addition, the PCE of unencapsulated PSCs after PEO treatment maintains 97% of its original stored in a nitrogen atmosphere for 1000 h.

The Effect of PEO Treatment in a Ta-Rich Electrolyte on the Surface and Corrosion Properties of Low-Carbon Steel for Potential Use as a Biomedical Material

Fe-based materials have extensive applications in the building and automobile industries due to their excellent mechanical properties and low cost. However, their biomedical employment is restricted by the corrosion propensity when in contact with bodily fluids. In this study, single-step Plasma Electrolytic Oxidation, PEO, treatment in Ta-rich electrolyte was used, for the first time, to improve the corrosion resistance of low-carbon steel SAE 1020 for possible use as device implants. The effect of the applied voltage on the chemical and phase composition, topography, wettability, roughness, and corrosion properties were addressed. The results indicated that the Fe-based oxide coatings had a rough and hydrophilic surface, increasing the Ta content with the applied potential. The phase composition of the coatings was mainly composed of hematite (Fe2O3), with the Fourier-transform Infrared Spectroscopy, FTIR, spectrums indicating the presence of some absorbed water and organic molecules. The corrosion resistance of the PEO-treated samples was better than the substrate against saline solution (0.9% NaCl) due to the Fe2O3 growth decorated with Ta particles, especially the sample treated at 200 V. The results state that Ta-enriched Fe-based oxide coatings could significantly improve the applicability of low-carbon steel SAE 1020 as a low-cost biomaterial, particularly for medical devices.

Role of glycerine on formation & corrosion characteristic of PEO layer formed over Mg alloy in a high-concentrated mixed silicate-phosphate-based electrolyte

PEO coatings on AM50 magnesium alloy were synthesized under constant current mode exploiting high-concentrated mixed silicate-phosphate-based alkaline electrolyte with and without glycerine as an additive, i.e., gmix-PEO and bmix-PEO respectively. The development of PEO coatings was studied as a function of PEO treatment time for their microstructures, element compositions, phase compositions, and corrosion behaviour. For all the treatment times, gmix-PEO exhibited relatively smaller pores and lower coating thickness than bmix-PEO. The elemental composition of PEO coatings was independent of PEO processing time for both bmix-PEO and gmix-PEO. Throughout PEO processing the incorporation of Si was considerably higher than P into the synthesized coatings. MgO and Mg2SiO4 crystalline phase content was higher for gmix-PEO compared to bmix-PEO for all the treatment times studied. A complex amorphous oxide phase was observed from 4 min PEO treatment time for bmix-PEO while glycerine addition delayed the formation of the same. The study of electrochemical behaviour revealed improved corrosion performance of gmix-PEO particularly during initial immersion (up to 25 h) time for up to 4 min PEO treatment time than for bmix-PEO as glycerine addition leads to higher MgO and Mg2SiO4 phase content and thicker/compact inner barrier layer. For the final 8 min PEO processing time, bmix-PEO offered enhanced corrosion performance particularly due to its thicker coating compared to gmix-PEO.

Effect of cathode pulse square-wave on the microstructure and corrosion resistance of PEO coatings of AZ91D magnesium alloy prepared in the Na2C4H4O6–KF–Na2SiO3 system

ABSTRACT Plasma electrolytic oxidation coatings were formed in Na2C4H4O6–KF–Na2SiO3 system on AZ91D magnesium alloy by controlling the single-pulse square-wave and bipolar pulse square-wave, respectively. Potentiodynamic polarisation (PD), electrochemical impedance spectroscopy (EIS) and electrochemical noise measurement (EN) were employed to investigate their corrosion behaviour in 3.5% NaCl solution. The results show that with bipolar pulse mode for PEO process, the growth rate of PEO coating on magnesium alloy first decreased and some micropores were present inside the PEO coating. With the increasing oxidation time, the PEO coating became much homogeneous and the porosity of the coating decreased largely, and the corrosion resistance of PEO coating was enhanced. The use of the bipolar pulse mode is beneficial to the improvement of the compactness and corrision performance of magnesium alloy with PEO treatment for the higher voltage stage and longer oxidation time.

Stabilizing and improving elastic bioengineered scaffolds mimicking extracellular matrix for use in wound repair and regeneration

AbstractElastic composite scaffolds are used to mimic extracellular matrix in tissue regeneration. They are composed of synthetic elastomers in favor of natural elastin. Many elastomers require thermal polymerization for fiber stabilization. If the scaffold contains protein, additional treatments are required for stabilization. These treatments may modify the structure and function of the scaffold. In the present study a protein‐elastomeric polymer composite of poly (glycerol sebacate), (PGS), silk fibroin, and type I collagen (termed PFC) was used as a model material to investigate a new method to improve stabilization of electrospun fibers. The purpose of this study was to optimize conditions in order to reduce internal flow of an elastomeric prepolymer during fiber fabrication. Co‐electrospun sacrificial poly (ethylene oxide) (PEO) was used to provide scaffold fiber stabilization during fiber formation in order to test different protocols to prevent fiber fusion. Using PEO at a 1:1 ratio with PFC followed by glutaraldehyde treatment, removal of PEO and heat treatment to polymerize PGS resulted in the most stable and consistent fiber morphology. Functionally, scaffolds had increased porosity and improved cell infiltration. The study provides an improved procedure for fabrication of composite electrospun scaffolds requiring stabilization by both chemical and thermal methods.

Effect of treatment time on a PEO‐coated AZ31 magnesium alloy

AbstractPlasma electrolytic oxidation (PEO) coatings were formed in a phosphate–silicate‐based electrolyte containing K2ZrF6 on an AZ31 Mg alloy. The physical and chemical properties of the coatings were investigated using scanning electron microscopy, atomic force microscopy, X‐ray diffraction (XRD), potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS). The results showed that the thickness of the PEO coatings increased linearly with increased treatment times. Additionally, the micropores on the coating surfaces increased in size, but decreased in porosity with increased PEO treatment time. The XRD results showed that the coatings were mainly composed of MgO, MgF2, MgSiO3, and ZrO2, and the electrochemical tests revealed that the corrosion resistance of the coatings increased with increased treatment time. Besides, the EIS results correlated well with the potentiodynamic polarization test results.

Effect of microstructure and porosity of AlSi10Mg alloy produced by selective laser melting on the corrosion properties of plasma electrolytic oxidation coatings

In this work, PEO process was carried out on SLM samples of AlSi10Mg, characterized by different grades of porosity, in direct-current mode using high current densities and short time in a basic silicate electrolyte. For comparison, the PEO process was also performed on samples of conventional cast AlSi10Mg alloy. The microstructure and the composition of the coatings was evaluated with SEM and XPS, whereas the phase analysis was performed with XRD. The corrosion resistance was analyzed by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) tests.The parameters used for PEO process allowed to obtain a continuous coating on all SLM samples, but its morphology resulted strongly influenced by the initial microstructure of the substrate. The coatings more homogeneous and less porous were produced on the samples with initial lower porosity. The corrosion performances of all SLM samples improved after PEO treatment and the PEO coatings with lower porosity resulted the more corrosion resistant.

Corrosion Behaviors of Zn, Si, and Mn-Doped Hydroxyapatite Coatings Formed on the Ti-6Al-4V Alloy by Plasma Electrolytic Oxidation.

Ti alloy for implant materials is not good biocompatibility between metal implants and natural bone without surface modification. In order to improve the bone attachment ability, implant surface modification is required, and corrosion resistance is also important when a surface modified implant is inserted into the body. In this study, corrosion behaviors of anodic oxide film formed on Ti-6Al-4V alloy with concentration of Mn and Zn ions were studied using various experimental techniques. Ti-6Al-4V ELI disk were used as the substrate for PEO treatment. The sample was used a anodic electrode and PEO treatment was carried out by varying the content of each of the electrolytic solutions containing Zn, Mn, Si, Ca and P, using a Pt bar as a cathodic electrode. Pulsed DC power was used at 280 V for 3 min. For the corrosion behaviors of the specimens, the potentiodynamic polarization and AC impedance test were carried out in 0.9% NaCl solution. From the result of experiments, as Zn ion content increases, the number of pores and the pore size increase. As the Mn ion increases, the number of pores decreases, while the pore size increases. As the ions of Mn increase, the corrosion potential decreases. As Zn ion content increased, the polarization resistance increased.

Plasma electrolytic oxidation of AZ31 and AZ91 magnesium alloys: Comparison of coatings formation mechanism

Abstract The growth kinetics of PEO coatings on AZ31 and AZ91 magnesium alloys were studied and correlated with their structure, compositions (phase and elemental) and corrosion resistance. It was established that the coatings have a two- (outer and anodic) or three-layer structure (outer, inner and anodic) depending on the treatment time. Briefly, at short treatment time only an anodic layer and outer layer exists. Growth of the outer PEO layer takes place due to the micro discharges, which occur in vertical pores and voids with spherical cross-section. If the time is increasing, and electrolyte inside of the pores is heating-up, etching of the Mg substrate and oxide film becomes more dominant and horizontal pores in the interface between coating and metal are formed. In the pores new anodic layer will form and at this time the formation of the third inner layer starts. The growth of the inner layer happens via the anodic film as a result of micro discharge ignition in the horizontal pores, accompanied by formation of plasma in numerous micro-voids of this layer. The coatings formed on AZ91 alloy are denser, than those on AZ31, which is related to the difference in the rates of inner layer growth and dissolving of oxides which are located at the bottom of the horizontal pores. Because of the lower Al content, the AZ31 substrate itself and the also the oxide films are less stable and tend to dissolve at a higher rate compared to AZ91. Thus, it was demonstrated that a good corrosion resistance of the coatings was only obtained on AZ91 and if the average thickness of the coating is around 50 µm, correlating with the formation of a sufficiently dense inner layer. Knowing this mechanism, a new two-step treatment was suggested, combining the standard PEO treatment with a subsequent PEO process in an electrolyte supporting the inner film formation. The concept was successfully applied and a further improved corrosion resistance was obtained compared to the single stage PEO process. This improvement of corrosion resistance was related to the better sealing of porosity and formation of a denser inner layer.

On the Stability of ZrO2 + TiO2 Coatings on Titanium Formed by Plasma Electrolytic Oxidation in a Chlorine-Containing Medium

The regularities of the effect of the duration of coatings' galvanostatic formation in Zr(SO4)2 electrolyte on their composition, structure, surface contact angle with water, and the time of emergence of electrostimulated pitting when samples are in contact with an aqueous NaCl solution have been studied. It has been shown that coatings formed on titanium in the range of transition from the sparkling stage to that of more powerful microarc electric discharges are relevant for anticorrosive properties. The interrelation between the anticorrosive properties of PEO coatings and the stages of their growth may be of general character in PEO treatment of valve metals and alloys of different nature in electrolytes with varying compositions.

Plasma electrolytic oxidation of Ti-6Al-4V alloy in electrolytes containing bone formation ions

In this study, plasma electrolytic oxidation of Ti-6Al-4V alloy in electrolytes containing bone formation ions was examined using various instruments. Here, a Ti-6Al-4V ELI disk is used for PEO treatment. A pulsed DC power of 280 V was applied to all specimens for 3 min. The electrolytes used for PEO were prepared by mixing of calcium, prosperous, silicon, strontium, zinc, magnesium, and manganese ions. Additionally, MC3T3-E1 mouse osteoblasts were cultured on the specimens for the cell proliferation assay. The morphology of the attached cells was observed using field-emission scanning electron microscopy (FE-SEM). The surface characterization of the PEO-treated surface was performed by FE-SEM and energy dispersive X-ray spectroscopy. The surface area of the pores was measured using an image analyzer. Furthermore, the phase of the specimen was analyzed with a thin film X-ray diffractometer (XRD).The PEO films, except the specimen containing manganese element, exhibit a uniform porous surface. The porous structure displays a very rough surface, and Mn easily precipitates around pores in the process of original and new pore formation. A high amount of Mn was detected in the precipitate inside the pores, whereas high amounts of calcium, phosphorus, strontium, titanium, and oxygen were detected around the pores. The XRD peak of HA on PEO-treated surface in the electrolyte containing the ions of five elements is lower, broader and shifted toward the left side. The pores were covered with MC3T3-E1 cells and extended well. Cells exhibit a spinning form of filopodia in lamellipodia and grow in association with the cells on PEO-treated surface in an electrolyte containing five ions. The cell differentiation and bone formation ability of ions of five elements doped surface were significantly increased compared to bulk surface.

Antimicrobial activity and mechanism of action of Perilla essential oil against Staphylococcus aureus

Staphylococcus aureus (S. aureus) is an important cause of foodborne illness in humans and animals. In some Asian countries, Perilla (Perilla frutescens) is widely used for cooking and medicinal purposes. The current study reports its antibacterial activity against S. aureus. PEO exhibited significant antibacterial activity against S. aureus with MIC values ranged from 1 to 2 mg/ml. Growth curve illustrated that PEO had time and concentration-dependent antibacterial effects against S. aureus. The results of this study showed that PEO exerted the inhibitory effect on S. aureus through cell membrane permeabilization which was associated with generalized membrane-disrupting effects, and this corresponded to a simultaneous loss of 260-nm absorbing materials. FCM assay also demonstrated that PEO treatment markedly damaged the membrane of S. aureus. Moreover, the SEM and TEM observations also support the above hypothesis, and strongly indicated the membrane-destructing activity of PEO. This study may contribute to the effective application of PEO as a natural antibacterial agent to control foodborne pathogens in food industries.