PEO Coatings Research Articles

Production and Characterization of Photocatalytic PEO Coatings Containing TiO2 Powders Recovered from Wastes

In this work, the possibility of incorporating TiO2 titanium dioxide particles derived from the recycling process of photovoltaic panels into PEO coatings was investigated. These particles constitute the main filler of the polymer constituting the rear part of the panels, and are characterized by possessing photocatalytic properties. The particles were added in different quantities to the electrolyte (a basic solution containing sodium silicate). The incorporation into the PEO coating produced on an aluminum alloy 1050, and the possibility of conferring photocatalytic properties to the surface of the samples were studied. The different samples were first characterized by optical microscope analysis, SEM and XRD and from the point of view of corrosion resistance by means of potentiodynamic tests. The photocatalytic properties of the samples were evaluated by monitoring the degradation of aqueous solutions of methylene blue exposed to a UV lamp. The particles have been successfully incorporated into the coating, and their presence does not alter the corrosion properties, which are improved compared to the uncoated sample. The particles, initially composed of a mixture of rutile and anatase, are instead transformed into rutile after incorporation due to the locally very high temperatures that can occur during the PEO process. In the samples obtained with higher quantities of titanium dioxide particles (60 and 80 g/L), a significant photocatalytic effect is observed with a significant reduction of methylene blue.

The Influence of Duration of Polarization Pulses on Structure and Electrochemical Properties of PEO Coating on ML5 Magnesium Alloy

The Influence of Duration of Polarization Pulses on Structure and Electrochemical Properties of PEO Coating on ML5 Magnesium Alloy

Electrochemical and mechanical properties of the PEO coatings containing halloysite nanotubes

Electrochemical and mechanical properties of the PEO coatings containing halloysite nanotubes

Effect of carbon nanotubes incorporation on the properties of the PEO coatings formed on MgMn-Ce alloy

The properties of coatings formed on the MA8 magnesium alloy by the plasma electrolytic oxidation in electrolytes containing multi-walled carbon nanotubes in concentrations of 2, 4 and 6 g/l have been investigated. It was found that the introduction of multi-walled carbon nanotubes leads to an increase in the adhesive strength, microhardness and Young’s modulus of the obtained layers.

Preparation of black thermal control PEO coatings on TC4 with enhanced electrical conductivity by gas thermal penetration post-treatment

The black thermal control coating with enhanced conductivity was prepared by PEO and gas thermal penetration post-treatment with methanol as carbon source. The structure and composition of coatings were tested and analyzed by SEM, TEM, XRD, XPS and Raman spectroscopy. The as-prepared composite coatings (C-PEO coating) retained the typical porous characteristics and were mainly possessed polycrystalline structure. During the penetration treatment, the decomposition of methanol led to the increase of graphitization degree of amorphous carbon and the formation of a carbon conductive network in the coating, and partial high valence metal oxides were reduced to low valence in the reducing atmosphere. Gas thermal penetration post-treatment improved the conductivity of the coating was mainly attributed to the carbon conductive network. The PEO coating after penetration treatment at 700 °C for 3 h had the lowest volume resistivity of 2.63 × 103 Ω·m, which also remained high absorptivity (200–2500 nm, 0.947) and emissivity (2.5–16 μm, 0.917). After electron irradiation, the mass loss of the coating was 0.033 g·m−2, and the absorptivity and emissivity only decreased to 0.946 and 0.911, respectively, indicating excellent anti-electron irradiation ability. This work opens a new road to improve the conductivity of PEO coating.

ZnAl-LDH@MXene modified by inhibitor as a nanofiller applied on Mg alloys coating protection

Recently, MXene/Epoxy coatings have attracted attention for its outstanding corrosion and wear resistance. However, the self-restacking tendency of MXene in epoxy resins affects the mechanical properties of coatings. Herein, ZnAl-LDH-NO3- nanosheets were grown on MXene by one-step hydrothermal method to inhibit its spontaneous aggregation, and then the ZnAl-LDH-NO3-@MXene mixed with epoxy resin was spun onto the pre-prepared Mg PEO coatings. ZnAl-LDH-NO3-@MXene nanocomposite had long-term dispersibility, resulting in a satisfactory sealing of the Mg PEO coatings. The lowest wear rate and corrosion current density of the final coating demonstrated that LDH and MXene nanosheets presented a good synergistic effect. Moreover, nitrate was simultaneously intercalated into the guest layer of the ZnAl-LDH providing a self-healing function. This work proposed a new strategy to solve the self-restacking of MXene and facilitate its anticorrosion/wear applications in epoxy coatings: that is MXene-based nanocomposite.

Anticorrosive lanthanum embedded PEO/GPTMS coating on magnesium alloy by plasma electrolytic oxidation with silanization

The different amount of lanthanum doped PEO coatings with and without 3-glycidyloxypropyltrimethoxysilane (GPTMS) layer were prepared on the AZ31 magnesium alloy to investigate the corrosion resistance of the resulting coatings. The SEM results revealed that the porosity of the PEO coating structure decreased with increase in La(NO 3 ) 3 content. The corrosion analysis of prepared coatings was performed using potentiodynamic polarization (PDS) and electrochemical impedance spectroscopy (EIS) methods. As a result of the PDS test, an anti-corrosion property of the coatings was sufficiently improved with the presence of La nanoparticle. The concentration of 0.7 g/l La(NO 3 ) 3 in PEO electrolyte produced coatings with lower porosity and higher anticorrosion property. The corrosion resistance of the coatings further improved with GPTMS layer. Corrosion current density for the PEO/GPTMS coating decreased by eight orders of magnitude compared to bare alloy. In addition, the noble potential of -0.25 V/Ag/AgCl was observed in the PEO/GPTMS coating. 0.7 g/l lanthanum contained and silane sealed P7LaS coating exhibited the highest corrosion resistance, which was 1.79×10 10 Ω.cm 2 . According to the EIS test, P7LaS coating showed higher resistance after 7 days of immersion in the corrosive solution compared to other coatings. Moreover, PEO/GPTMS coatings presented better resistance during the immersion due to their proper GPTMS barrier layer in compared to GPTMS-free PEO coatings. Adding a higher concentration of La in PEO electrolyte and consequent GPTMS sealing was an efficient approach for enhancing the corrosion protection properties of PEO coating.

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.

Systematic Investigation of Silicon Content Effects on the PEO Coatings’ Properties on Al–Si Binary Alloys in Silicate-Based and Tungstate-Containing Electrolytes

The present study evaluates the effect of a substrate’s silicon content on the coatings’ morphology, structure, and properties in an electrolyte containing sodium tungstate on Al–xSi alloys. The PEO-coated samples demonstrated the structure of the pancake and crater with irregular micro-cracks and micro-pores. The incorporation of the element W in the coatings decreased the surface roughness and porosity due to increasing the electrolyte conductivity and, hence, decreasing the breakdown voltage and intensity of micro-discharges. The friction coefficient of all the coatings stayed constant during the wear test due to the contact of the ball with the inner layer with less porosity and higher micro-hardness. The track depth to the thickness ratio of the coatings was found to be 0.60–0.75 for those without additive coatings and 0.55–0.65 for those with additive coatings. As a result, the higher wear rates, volume losses, track widths, and depths in the specimens with a lower silicon content of the substrate were found due to the greater thickness of the coating and the outer sublayer for both specimens with and without Na2WO4. The coatings formed using the W-containing electrolyte showed a higher micro-hardness and a lower wear rate in comparison with the coatings produced in the silicate-based electrolyte.

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.

Dissolution Behavior of Different Alumina Phases within Plasma Electrolytic Oxidation Coatings

The influence of chemical redissolution in the PEO layer-growth equilibrium on aluminum is evaluated differently in literature. In order to estimate whether and to what extent various alumina modifications could be affected by redissolution processes during PEO, immersion experiments were carried out on PEO coatings in model electrolytes of different alkalinity and silicate concentration. Their composition was determined spectroscopically before and after the experiments. The layers were characterized by XRD before and after the tests and examined at affected and unaffected zones using SEM, EDX, and EBSD. The results show that chemical oxide dissolution can only be observed at the layer/substrate interface and that primarily amorphous alumina is affected. This process is intensified by higher alkalinity and inhibited by silicate additives. The crystalline Al2O3 modifications show no significant attack by the electrolytes used. Transferring these observations to plasma electrolytic oxidation, they allow the conclusion that the electrochemically active zone in the pore ground of discharge channels interacts with the electrolytic and electrical process parameters throughout the entire PEO procedure. Influences of bath alkalinity and silicate content on layer growth rates are to be understood as impact on the passivation processes at the layer/substrate interface rather than chemical redissolution.

Corrosion and tribocorrosion protection of novel PEO coatings on a secondary cast Al-Si alloy: Influence of polishing and sol-gel sealing

PEO coatings have been developed on a secondary cast Al-Si alloy, using a novel aluminate-based electrolyte, containing Na4P2O7, Na2WO4 and K2TiF6. The protective performance of the PEO coatings has been improved throughout the application of two post-treatments: polishing of the outermost coating layer and sealing with a sol-gel layer. While the sol-gel has notably improved the corrosion resistance and dielectric properties, due to the sealing of surface pores, the decrease in surface roughness achieved by polishing have enhanced the tribocorrosion performance. The post-treatments studied would enable the future application of PEO coatings on components with high requirements in corrosive environments.

Development and screening of (Ca-P-Si-F)-PEO coatings for biodegradability control of Mg-Zn-Ca alloys

• Transparent electrolytes containing bioactive agents were developed for PEO of MgZn x Ca y alloys. • AC PEO on MgZnCa and Mg3Zn0.4Ca cast alloys showed a linear coating growth kinetics. • Permeability and insufficient stability of the barrier layer allows undercoating corrosion. • No influence of organic components of α-MEM on Mg alloy/PEO corrosion resistance. PEO coatings were developed on MgZn x Ca y alloys for biomedical applications using different treatment times and a novel transparent electrolyte containing Ca, P, Si and F. Surface characteristics and chemical composition of studied materials were evaluated using scanning electron microscopy, X-ray diffraction and optical metrology. Corrosion investigations were performed for uncoated and coated materials using potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements in three media (0.9wt.% NaCl, α-MEM and inorganic part of α-MEM). Findings revealed that Zn-rich intermetallics favour the formation of large voids in the coatings. Ca, P, F and Si are successfully incorporated into the coatings. Coatings consist of crystalline phases (MgO, MgF 2 and Ca,Si-rich compounds) and amorphous material. Aminoacids and organic components of α-MEM solution accelerate corrosion of the bare substrates but have no significant influence on the corrosion resistance of coated specimens. Therefore, inorganic α-MEM can be considered as an appropriate medium for fast screening of PEO coatings. The relatively small amount of F content in the barrier layer facilitates early failure of the coatings, which show undercoating corrosion. Zn-rich intermetallic particles in the undercoating crevice induce a more aggressive corrosive environment and enhanced micro-galvanic couple effect with the Mg matrix. This leads to faster degradation of the coated alloys compared to the bare substrates.

Single Dense Layer of PEO Coating on Aluminum Fabricated by "Chain-like" Discharges.

Reducing the loose-layer-to-dense-layer ratio in PEO coatings on aluminum and its alloys is the key to improving their corrosion resistance and expanding their applications in the aerospace industry and other fields. In this paper, we describe the discharge evolution during the PEO process in exhaustive detail and report the appearance of a novel “chain-like” discharge for the first time. We investigated the microstructure and composition of PEO coatings using a scanning electron microscope (SEM) equipped with an energy-dispersive spectrometer (EDS) and an X-ray diffractometer (XRD). The results reflected that the coating composition changed from amorphous Al2O3 to crystalline γ-Al2O3 and α-Al2O3 phases with the evolution of the plasma spark discharge state. We evaluated the electrochemical behavior of the coatings using a potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. Under “chain-like” discharge, the icorr of the coating on Al was 8.564 × 10–9 A∙cm−2, which was five orders of magnitude lower than that of the sample without the PEO coating. Moreover, we evaluated the adhesion strength of the coatings at different stages using a pull-off test. The adhesion strength of the PEO coatings at stage V reached 70 MPa. Furthermore, the high content of α-Al2O3 increased the hardness of the coating to 2000 HV. Therefore, the “chain-like” discharge promoted the formation of a single dense layer with 2.8% porosity and that demonstrated excellent properties. We also propose a mechanism to explain the influence of the plasma spark discharge state on the microstructure and composition of the PEO coatings.

Effect of AZ31 PEO Coating Layer Formation According to Alginic Acid Concentration in Electrolyte Solution

Effect of AZ31 PEO Coating Layer Formation According to Alginic Acid Concentration in Electrolyte Solution

Role of phosphate, silicate and aluminate in the electrolytes on PEO coating formation and properties of coated Ti6Al4V alloy

A comparison of PEO layers on Ti6Al4V alloy formed in phosphate, aluminate and silicate-based electrolytes respectively, has been made to reveal the influence of the electrolyte composition on the formation process. The phosphate-based electrolyte has been identified as the most promising one as it has the best coating formation efficiency and the lowest breakdown voltage. On the bases of the microstructure and elemental/phase analysis of the different PEO coatings, it could be observed that the PEO coating formed in phosphate-based electrolyte is mainly composed of anatase and rutile. An amorphous phase is dominant in the coating produced in silicate-based electrolyte. Moreover, there are mainly γ-Al2O3, Na2Al2xO3x+1 and TiAl2O5 present in the coating formed in the aluminate-based electrolyte. The coating formation process in silicate- and aluminate-based electrolytes is more dependent on the deposition originating from the electrolytes. All of the coatings have shown noticeable corrosion resistance and good performance in the photocatalytic test as the degradation rates of methyl orange higher than 45 %. Thus, multifunctional PEO coatings on Ti6Al4V alloy are obtained.

Effect of carbon nanotubes on the microstructure and properties of plasma electrolytic oxidized ceramic coatings on high silicon aluminum alloy

Ceramic coatings with carbon nanotubes were prepared on high silicon aluminum alloy by plasma electrolytic oxidation. The microstructure, phase, and elemental compositions of the matrix and ceramic coatings were characterized by metallographic microscope, X-ray diffraction, field emission scanning electron microscope, micro confocal Raman spectrometer and energy dispersive spectrometer. The functional groups contained in the coating were characterized using Fourier infrared spectrometer and X-ray photoelectron spectroscopy. The electrochemical workstation and thermal conductivity meter were employed to study the corrosion resistance and thermal conductivity of ceramic coatings. The effect of CNTs on the morphology, microstructure, coating formation and growth, corrosion resistance and thermal conductivity of PEO coatings on ADC12 Al alloy was investigated. The results showed that the micropores on the surface of the PEO coating can be used as discharge channels for various migrating ions and particle groups in the electrolyte to participate in the formation and inward and outward growth of the coatings. CNTs participated in the formation and growth of ceramic coating by surface adsorption, melt wrapping and fusion reaction during the plasma electrolytic oxidation process. The coating contains mainly α-Al2O3, γ-Al2O3, SiO2 and small amount of SiC phases. The changes of electrochemical corrosion and thermal conductivity of the PEO coatings are related to the regulation of the coating microstructure by CNTs.

Improving the Corrosion Properties of AZ91 Magnesium Alloy by Coating CrN/NbN with PEO and PVD Duplex Coating Methods

Otomobil, havacılık ve havacılık endüstrilerinde geleneksel mühendislik malzemelerinin geliştirilmesi ve uygulanması teknolojik altyapıyı desteklemiştir. Yüksek özgül mukavemete sahip magnezyum alaşımlarının kullanılması, özellikle ileri mühendislik uygulamalarında düşük ağırlıklı tasarımlar üretmek için çok önemlidir. Ancak magnezyum alaşımlarının korozyona karşı yüksek afinitesi kullanım alanını sınırlar. Son zamanlarda, fiziksel buhar biriktirme (PVD) ve plazma elektrolitik oksidasyon (PEO) kaplama sistemleri, metalik malzemelerin korozyon özelliklerini iyileştirmiştir. Bu çalışmada AZ91 magnezyum alaşımı önce PEO yöntemi ile kaplandıktan sonra PVD sisteminde iki farklı magnetron (Niobium ve Chromium) ile kaplanmıştır. AZ91 magnezyum alaşımının korozyon direncini artırmak için PEO ve CrN / NbN kaplamaların korozyon davranışına etkisi% 3,5 NaCl çözeltisinde araştırılmıştır. CrN / NbN çok katmanlı kaplamanın PEO üzerindeki korozyon direncinin AZ91 magnezyum alaşımındakinden daha iyi olduğu belirlendi.

Influence of Cr2O3 particles on corrosion, mechanical and thermal control properties of green PEO coatings on Mg alloy

The influence of micro-sized Cr 2 O 3 particles on the corrosion, mechanical and thermal control performance of plasma electrolytic oxidation coated Mg was studied. More contents of Cr 2 O 3 particles were embedded into phosphate containing PEO coatings compared with coatings produced from silicate based electrolytes, resulting in green coatings with enhanced thermal control and mechanical property. The existence of particles has slightly improved the corrosion resistance and hardness of the coating. It was found that the absorptance of the coating was increased if higher concentration of Cr 2 O 3 particles is incorporated into the layer, which is probably ascribed to low band gap of Cr 2 O 3 .

Influence of sodium pentaborate (B5H10NaO13) additive in plasma electrolytic oxidation process on WE43 magnesium alloys

In recent years, the effects of adding various nanoparticles and chemicals dissolved in electrolytes to these chemicals have been investigated. In this paper, the idea of the effect of the sodium pentaborate (B5H10NaO13) in the NaAlO2 + KOH electrolyte PEO coating on the WE43 magnesium alloy was proposed. The tribological and corrosion properties of the grown coatings were investigated. Coating morphology, tribological properties, adhesion, and corrosion properties of the grown coatings were investigated by using SEM-EDS, ball-on-disc wear testing, scratch testing, and potentiodynamic corrosion testing. The results evidence that B5H10NaO13 additive, grown on magnesium substrate, supports the formation of hard oxide compounds such as MgAl2O4·BxOy. These structures grown on the WE43 alloy were determined to provide similar corrosion protection with non-additive PEO coatings and approximately 30 times lower wear rate than non-additive PEO coatings. Experimental results evidence the B5H10NaO13 can be used as an electrolyte additive to the PEO process in the field of advanced functional coating materials for tribological applications.