Plasma Electrolytic Oxidation Process Parameters Research Articles

Ceramic metal oxide coatings formation by hybrid plasma electrolytic treatment: Interaction scenarios of ceramic NPs with oxide layers

Understanding the formation of protective ceramic metal oxide (CMO) coatings (layers) on the surface of light alloys remains a pressing task in light of products operating in extreme conditions. Plasma electrolytic oxidation (PEO) of light alloy surfaces has recently been modified by introducing various ceramic nanoparticles (NPs) into the electrolyte to perform hybrid plasma electrolytic treatment (HPET). In this work, the general and distinctive features of the interaction mechanisms of TiC, SiO2 and ZrO2 nanoparticles (NPs) with the CMO coating formed by HPET of Al–Si and Mg-based alloys were summarized and theoretically substantiated. The interaction of charged ceramic NPs accelerated by an electric field with the oxide layer is determined by transformation of the NPs kinetic energy into heating and plastic deformation, into phase transformations, as well as into the creation of new surface defects. One of the controlling factors is the ratio of the particle and the oxide layer hardnesses. In the case of SiO2 in Al–Si alloys, the formed coating is harder than the ceramic NPs while in other cases, the NPs are harder than the CMO coating, which determines the different scenarios for the interaction of NPs with the coating under HPET. In summary 7 different scenarios for the interaction of ceramic NPs added to the electrolyte with the СМO layer during its formation put forward, which depending on the ratio of the hardness of the CMO layer and the added particles, temperature/pressure conditions of the phase transformations in the NP (including its melting), the particles size distribution and the base PEO process parameters.

Craniofacial reconstruction using 3D personalized implants with enhanced surface properties: Technological and clinical aspects

In this study, the modification of personalized titanium implants was developed using the plasma electrolytic oxidation process. Plasma electrolytic oxidation process parameters were initially optimized using solid samples of the Ti6Al4V alloy. Oxidation was achieved in an electrolyte containing calcium and phosphorus compounds at 250 V. The oxide layer produced was characterized by the use of human osteoblasts and fibroblasts, with high biological activity of the modified titanium alloy in relation to these cells was demonstrated. Based on tomographic examinations, models were made and then personalized implants for three patients were printed from a Ti6Al4V alloy powder. These implants were subjected to plasma electrolytic oxidation treatment within the previously developed parameters and surgically placed in the craniofacial area. On the basis of postoperative studies, surgical interventions were successful, with modification of the surface using the plasma electrolytic oxidation method producing bioactive surfaces for both bone and soft tissue.

Photoluminescent Coatings on Zinc Alloy Prepared by Plasma Electrolytic Oxidation in Aluminate Electrolyte

Thick ZnO/ZnAl2O4 coatings were synthesized on zinc alloy Z1 substrates through plasma electrolytic oxidation (PEO) for different anodization times. The prepared coatings were characterized by scanning SEM, XRD, diffuse reflectance and photoluminescence spectroscopy in order to establish the relationship between their structural and optical properties and PEO processing parameters. Under different PEO processing conditions (anodization time—1–10 min and applied voltage—370 and 450 V) ceramic coatings with a mean thickness of 2–12 μm were prepared. XRD analysis explored the coating structure composed of zinc oxide (wurtzite) and zinc aluminate spinel. The content of ZnAl2O4 in the coatings grows with increasing the applied voltage and anodization time. Photoluminescence (PL) measurements showed that the PEO coatings have several bands in the visible and near-infrared regions associated with their composite structure. The PL spectra significantly depend on the PEO processing parameters due to varying ZnO and ZnAl2O4 content in the coatings. The insight in the relationship between the ZnAl2O4 structure and the photoluminescent properties of ZnO/ZnAl2O4 coatings has been provided using the combination of XRD and luminescence spectroscopy.

Photoluminescent Plasma Electrolytic Oxidation Coatings Containing YAG: Ce Produced on 1050 Aluminum Alloy

In this work, we investigated the possible incorporation of YAG (yttrium aluminum garnet)-Ce particles into plasma electrolytic oxidation (PEO) coatings on 1050AA (aluminum alloy) in order to endow the surface with photoluminescent properties. Different treatment times and current modes (direct or pulsed) were tested as PEO process parameters using as electrolyte a silicates-containing solution. The microstructure of the samples was characterized by SEM and XRD measurements, the corrosion properties were determined by EIS tests, whereas the photoluminescence was evaluated with a proper spectrometer. The concentration of the YAG-Ce particles incorporated in the PEO coating was strongly influenced by the current mode, and in particular, it was higher with pulsed current mode. A higher content of YAG-Ce particles results in a better corrosion resistance and photoluminescent effect. PEO process in pulsed unipolar mode using an electrolyte containing YAG-Ce particles resulted an effective way to produce samples of 1050AA with a surface characterized by photoluminescent properties.

The effects of plasma electrolytically oxidized layers containing Sr and Ca on the osteogenic behavior of selective laser melted Ti6Al4V porous implants

Surface biofunctionalization is frequently applied to enhance the functionality and longevity of orthopedic implants. Here, we investigated the osteogenic effects of additively manufactured porous Ti6Al4V implants whose surfaces were biofunctionalized using plasma electrolytic oxidation (PEO) in Ca/P-based electrolytes with or without strontium. Various levels of Sr and Ca were incorporated in the oxide layers by using different current densities and oxidation times. Increasing the current density and oxidation time resulted in thicker titanium oxide layers and enhanced the release of Ca2+ and Sr2+. Biofunctionalization with strontium resulted in enhanced pore density, a thinner TiO2 layer, four-fold reduced release of Ca2+, and mainly anatase phases as compared to implants biofunctionalized in electrolytes containing solely Ca/P species under otherwise similar conditions. Different current densities and oxidation times significantly increased the osteogenic differentiation of MC3T3-E1 cells on implants biofunctionalized with strontium, when the PEO treatment was performed with a current density of 20 A/dm2 for 5 and 10 min as well as for a current density of 40 A/dm2 for 5 min. Therefore, addition of Sr in the PEO electrolyte and control of the PEO processing parameters represent a promising way to optimize the surface morphology and osteogenic activity of future porous AM implants.

Effects of processing parameters on the adhesion and corrosion resistance of oxide coatings grown by plasma electrolytic oxidation on AZ31 magnesium alloys

In this work, the plasma electrolytic oxidation (PEO) process using a pulsed bipolar direct current (DC) power supply and sodium aluminate-based electrolyte was employed to grow the oxide layer on the AZ31 Mg alloy. For achieving a higher adhesion or a better corrosion resistance of oxide layer, the Taguchi L9 orthogonal array was adopted to determine the optimal PEO parameters, including anode on-time, anode current setting, cathode current setting, and cathode on-time. According to the signal-to-noise ratio and analysis of variance, the anode on-time was the most important control factor for improving adhesion and corrosion resistance properties of oxide coatings. The surface morphologies of all oxide coatings were typical crater-like microstructures. The oxide layer thickness can be increased by longer anode on-time and higher anode current. The hardness of the oxide layer was between 12.7 and 17.7 GPa due to the formation of MgAl2O4 phase. Through the confirmation experiments using the optimized PEO processing parameters, the maximum adhesion critical load of 41.8 N can be obtained. On the other hand, the highest polarization resistance of 6.68 × 103 kΩ˙cm2 was achieved, which was 6485 times better than the bare AZ31 substrate due to its compact microstructure, and a dense and continuous inner barrier layer at the coating/substrate interface.

Effect of plasma electrolytic oxidation process on surface characteristics and tribological behavior

Plasma electrolytic oxidation (PEO) produces oxide ceramic coatings on lightweight Al alloys with high hardness, low thermal conductivity and dimple-like surface morphology. By changing PEO process parameters, coating surface morphology can be manipulated for friction reduction. This study uses both unipolar and bipolar current modes to prepare oxide coatings on Al-Si alloy samples with different durations in order to obtain surface textures with different dimple sizes and densities. The results indicate that decreasing actual contact areas of the coating surfaces and their counterparts lowers the coefficient of friction. The real contact areas, which can be observed in the frequency density distribution histograms and curves of the surface profile data, were different initially and then varied during the sliding tests in progress. More negatively and downwardly shifted maximum values on the probability density distribution function curve of a coating surface profile indicate less real contact area and thus a smaller coefficient of friction. Hardness also plays a factor in frictional behavior.

The Influence of the Electrolyte Nature and PEO Process Parameters on Properties of Anodized Ti-15Mo Alloy Intended for Biomedical Applications

Plasma electrolytic oxidation (PEO) of Ti-15Mo alloys conducted in electrolytes containing Ca and P compounds can be an efficient process with which to obtain bioactive coatings. This paper reports on the influence of the nature of the electrolyte, its concentration, and PEO process parameters on the properties of anodized layers on Ti-15Mo. A wide range of Ca- and P-containing alkaline and acidic solutions was employed to incorporate Ca and P ions into the anodized layer. The efficiency of the incorporation was evaluated by the Ca/P ratio in the coating as compared to that in the electrolyte. It was found that alkaline solutions are not suitable electrolytes for the formation of good quality, uniform PEO coatings. Only acidic electrolytes are appropriate for obtaining well-adherent homogeneous layers on Ti-15Mo. However, the maximum Ca/P ratios reached in the coatings were rather low (close to 1). The variation of electrical signal (negative-to-positive current ratio, frequency) and time of electrolysis do not result in a substantial change of this value. The processing time, however, did influence the coating thickness. Despite their low Ca/P ratio, the anodized layers demonstrate good biological activity, comparable to pure microrough titanium.

Effect of Process Parameters on the Corrosion Resistance Properties of PEO Coatings Produced on AZ31B Magnesium Alloy

Plasma electrolytic oxidation (PEO) can reduce the corrosion susceptibility of Mg alloys by producing a protective oxide layer. The present investigation examined the influence of PEO processing parameters on the corrosion resistance of the resulting coatings. Changes in the oxidation time, applied current density, and electrolyte temperature were shown to alter the thickness of the coating as well as its phase composition. Increasing the coating time was found to increase the thickness and uniformity of the coating. Application of a greater current density was found to increase the thickness of the outer layer, resulting in a more porous structure with reduced corrosion resistance. Elevating the temperature of the electrolyte resulted in partial dissolution of the coating, producing a thinner coating than that produced in an electrolyte at a lower temperature. The resistance to corrosion initiation was considered to be related to through-film pores in the coating, via electrochemical impedance modelling.

Incorporation of Ca, P, and Si on bioactive coatings produced by plasma electrolytic oxidation: The role of electrolyte concentration and treatment duration.

The objectives of the present study were to produce bioactive coatings in solutions containing Ca, P, and Si by plasma electrolytic oxidation (PEO) on commercially pure titanium, to investigate the influence of different electrolytes concentration and treatment duration on the produced anodic films and to evaluate biocompatibility properties. The anodic films were characterized using scanning electron microscopy, energy-dispersive spectroscopy, atomic force microscopy, and x-ray diffraction and x-ray photoelectron spectroscopies. The surface energy and roughness were also evaluated. PEO process parameters influenced the crystalline structure formation and surface topography of the anodic films. Higher Ca content produced larger porous (volcanolike appearance) and thicker oxide layers when compared to the lower content. Treatment duration did not produce any topography difference. The treatment modified the surface chemistry, producing an enriched oxide layer with bioactive elements in the form of phosphate compounds, which may be responsible for mimicking bone surface. In addition, a rough surface with increased surface energy was generated. Optimal spreading and proliferation of human mesenchymal stem cells was achieved by PEO treatment, demonstrating excellent biocompatibility of the surface. The main finding is that the biofunctionalization with higher Ca/P on Ti-surface can improve surface features, potentially considered as a candidate for dental implants.

Application of porous oxide layer in plastic/metal direct adhesion by injection molding

In this study, porous oxide layers were coated on aluminum sheets by plasma electrolytic oxidation (PEO) treatment. The PEO-treated aluminum sheets were then inserted and direct heated in the injection mold. The melting plastic penetrated and solidified in the micropores during the injection molding process, consequently achieving plastic/metal direct adhesion through micro-mechanical interlocking. The effects of the different surface morphologies of PEO coatings on plastic/metal adhesion were studied by shear test and microscopic characterizations. The microstructures were varied by changing PEO process parameters. The bonding strength was affected by the surface morphology changes, and the experimental results show that the surface porosity is a major factor in the direct adhesion. Reliable joints can be achieved on the porous coating, and the strength was proportional to the surface porosity. The shear strength in this study was in a range of approximately 3–8 MPa with 7–20% surface porosity.

Bioactivity of coatings formed on Ti-13Nb-13Zr alloy using plasma electrolytic oxidation.

In this work, we investigated the bioactivity of anodic oxide coatings on Ti-13Nb-13Zr alloy by plasma electrolytic oxidation (PEO) in solutions containing Ca and P. The bioactive properties of the films were determined by immersion in simulated body fluid (SBF), and their biocompatibility was examined using adult human bone marrow derived mesenchymal stem cells (hBMSCs). The oxide layers were characterised based on their surface morphology (SEM, AFM, profilometry) as well as on their chemical and phase compositions (EDX, XRF, XRD, XPS). We report that anodic oxidation of Ti-13Nb-13Zr led to the development of relatively thick anodic oxide films that were enriched in Ca and P in the form of phosphate compounds. Furthermore, the treatment generated rough surfaces with a significant amount of open pores. The surfaces were essentially amorphous, with small amounts of crystalline phases (anatase and rutile) being observed, depending on the PEO process parameters. SBF soaking led to the precipitation of small crystals after one week of experiment. During culturing of hBMSCs on the bioactive Ti-13Nb-13Zr surfaces the differentiation of human mesenchymal stem cells toward osteoblasts was promoted, which indicated a potential of the modified materials to improve implant osseointegration.

The effect of processing parameters and substrate composition on the corrosion resistance of plasma electrolytic oxidation (PEO) coated magnesium alloys

Magnesium alloys are considered one of the more promising materials for future use in many engineering applications. However, due to their high chemical and electrochemical reactivity, magnesium alloys have poor corrosion resistance in aqueous environments. Improving their corrosion resistance by coating can greatly extend their application. One promising coating method is plasma electrolytic oxidation (PEO). The nature of the coating formed, and the ultimate corrosion performance depends on the both the processing parameters (electrolyte, current density, current mode, processing time) and specific Mg-alloy substrate. In the present study, PEO coatings were produced on three different Mg-alloys (AJ62, AM60B and AZ91D) using different processing parameters. Scanning electron microscopy was used to characterize the coatings. The corrosion resistance was evaluated using electrochemical impedance spectroscopy (EIS) in an aqueous 3.5% NaCl solution. Relationships are drawn between PEO processing parameters, substrate composition and corrosion performance. Electrochemical impedance spectroscopy data indicate that the bipolar PEO coated AZ91D Mg alloy demonstrates a higher corrosion resistance when compared to coated AM60B, AJ62 and pure Mg.

Tribocorrosion behaviour of anodic titanium oxide films produced by plasma electrolytic oxidation for dental implants

ABSTRACTCommercially pure Titanium (cp‐Ti) and its alloys are the materials most widely used for dental implant applications. In the present work, anodic oxide films have been produced on cp‐Ti surfaces by plasma electrolytic oxidation (PEO) technique. After PEO treatments, oxide films with different surface features (e.g. surface roughness, morphology and film thickness) were obtained according with anodising parameters. The tribocorrosion behaviour of untreated and PEO‐treated Ti samples was investigated by reciprocating sliding tests performed in artificial saliva. PEO treatments significantly improved the performance of cp‐Ti substrates when they were submitted simultaneously to electrochemical and mechanical effects, and it was influenced by PEO processing parameters. PEO seems to be a very attractive technique for the development of bio‐tribocorrosion resistant Ti surfaces with potential for biomedical applications namely, for dental implants. Copyright © 2013 John Wiley & Sons, Ltd.

TEM analysis and tribological properties of Plasma Electrolytic Oxidation (PEO) coatings on a magnesium engine AJ62 alloy

In order to reduce the fuel consumption and pollution, automotive companies are developing magnesium-intensive components. However, due to the low wear resistance of the magnesium (Mg) alloys, Mg cylinder bores are vulnerable to the sliding wear attack. In this paper, a Plasma Electrolytic Oxidation (PEO) process was used to produce oxide coatings on a Mg alloy AJ62 (MgAl6Mn0.34Sr2), developed for Mg engine block, to battle against the wear attack. The surface morphology, coating thickness and tribological properties were tailored by adjusting the PEO process parameters. TEM analysis demonstrated that the PEO coatings had a nanocrystalline structure in the inner dense layer next to the substrate. The PEO coatings exhibited a much better wear resistance and a smaller friction coefficient than the uncoated AJ62 substrate. The tribological performance of the PEO-coated Mg alloy was even better than that of a hypereutectic Al–Si alloy currently used for engine applications under a high contact load.

The effect of substrate composition on the electrochemical and mechanical properties of PEO coatings on Mg alloys

Abstract Plasma electrolytic oxidation (PEO) is a unique surface treatment technology which is based on anodic oxidation forming ceramic oxide coatings on the surface of light alloys such as Mg, Al and Ti. In the present study, PEO coatings prepared on AZ91D, AZ31B, AM60B and AM50B Mg alloys have been investigated. Surface morphology and elemental composition of coatings were determined using scanning electron microscope (SEM) equipped with energy dispersive spectrometer (EDS). SEM results showed that the coating exhibited a porous top surface layer and a subsequent dense layer with micro-pores and shrinkage cracks. Phase analysis of coatings was carried out by X-ray diffraction (XRD). XRD analyses indicated that PEO coatings on AZ alloys had higher amount of Periclase (MgO) followed by the presence of Spinel (MgAl 2 O 4 ) e.g. on the AZ91D alloy compared to that on AM series alloys. In order to examine the effect of substrate composition on adhesion strength of PEO coating scratch tests were carried out. Electrochemical corrosion tests were undertaken by means of potentiodynamic polarization technique in 3.5% NaCl solution at room temperature (20 ± 2 °C). Corrosion test results indicated that the corrosion rates of coated Mg alloys decreased by nearly two orders of magnitude as compared to bare Mg alloys. PEO coatings on AZ series alloys showed better corrosion resistance and higher adhesion properties than AM series alloys. In addition to the PEO processing parameters, such are mainly attributes of the compositional variations of the substrate alloys which are responsible for the formation, phase contents and structural properties of the PEO coatings.