Effect Of Plasma Electrolytic Oxidation Research Articles

Effect of plasma-electrolytic oxidation on mechanical properties of titanium coatings

The process of plasma electrolytic oxidation (PEO) allows to obtain multifunctional coatings with unique properties, including wear-resistant, corrosion-resistant, heat-resistant, electrical insulating and decorative. Therefore, the field of application of these coatings is quite wide: medicine, aircraft construction, shipbuilding, instrumentation, automotive and other industries. The technology is based on the phenomenon of micro-arc discharges promoting the formation of oxide layers on metal surfaces. In this review the technologies of obtaining coatings by plasma electrolytic oxidation on titanium are considered. The experiment on PEO of VT1-0 titanium substrate under anodic treatment with the addition of TiO2 nanoparticles to the electrolyte was carried out. Dense, uniform oxide coatings that do not require additional surface grinding were obtained. The coating thickness values were 18.5-62.4 μm. The influence of PEO on the microhardness of calcium-phosphate coatings formed as a result of this treatment was studied. With a satisfactory thickness of the formed layer (62.4 μm), the surface microhardness value (4.04 GPa) was found to be the highest among all the treatment modes compared, simultaneously with a high elastic modulus value (348 GPa) and a small value of the indenter penetration depth on the coating (968.99 nm). These coatings were formed in an electrolyte containing calcium phosphate with the addition of 0.75g of titanium oxide nanoparticles. The increase of microhardness in comparison with the sample without coating is in 2,5 times. As a result of the carried out researches optimum modes and parameters of calcium-phosphate coatings receiving have been established and defined. It is shown that by changing the composition of the electrolyte of the micro-arc treatment process it is possible to influence significantly the structure, thickness and surface properties of the obtained coatings.

Effect of Plasma Electrolytic Oxidation on the Short-Term Corrosion Behaviour of AZ91 Magnesium Alloy in Aggressive Chloride Environment

In order to increase the corrosion resistance of magnesium alloy AZ91 in corrosion environments containing chlorides, the alloy surface has been modified by plasma electrolytic oxidation (PEO). The chemical composition of electrolyte in the PEO process consisted of 12 g/L Na3PO4·12 H2O and 1 g/L KOH, and a direct current was applied to the sample. The corrosion resistance of PEO coating and as-cast AZ91 (sample without PEO coating) was assessed using two different electrochemical methods: electrochemical impedance spectroscopy (EIS) and potentiodynamic polarisation (PDP) in 0.1 M NaCl at laboratory temperature. In addition to the electrochemical methods, the morphology of the oxidic coating was observed in the cross-sectional and top surface view by using the SEM technique. For better determination of the microstructure and PEO coating, chemical composition EDX analysis was used. The results of the experiments show that the formation of the PEO coating on AZ91 alloy has a more positive effect on the corrosion resistance in 0.1 M NaCl based on electrochemical methods than in the case of the formed coating on AZ31 alloy from the previous study. Based on electrochemical measurements in the selected environment, the formation of PEO coating on AZ91 was accompanied by a significant increase in polarisation resistance after short-term exposure compared to the as-cast surface. The EIS results showed a 73 times higher Rp value for PEO coated AZ91 when compared to the as-cast AZ91. Correspondingly, a 27 times lower icorr value was observed for PEO coated AZ91 than in the case of substrate AZ91 in 0.1 M NaCl. At the same time, the typically porous and inhomogeneous structure of the formed PEO coating on the magnesium alloy AZ91 was demonstrated.

Effect of plasma electrolytic oxidation on the hot salt corrosion fatigue behavior of the TC17 titanium alloy

AbstractIn this paper, the effect of plasma electrolytic oxidation (PEO) on the hot salt corrosion fatigue (HSCF) behavior of the TC17 titanium alloy at 420°C was investigated. Through microstructure characterization and fatigue fracture analysis, combined with a comparative study of its hot salt corrosion behavior, the mechanism of PEO on HSCF behavior was also investigated. The results showed that the high‐temperature fatigue resistance of the TC17 titanium alloy was significantly reduced by the deposition of 0.4 mg/cm2 of solid NaCl compared with that without a salt coating. This behavior was observed because the corrosion pits caused by hot salt corrosion promoted the initiation of fatigue cracks, and hydrogen penetration promoted the growth of fatigue cracks. However, the HSCF resistance of the TC17 alloy with the PEO ceramic coating could be effectively increased. This was because the PEO ceramic coating with high bonding strength and good compactness effectively inhibited hot salt corrosion damage and delayed the formation of the resident slip zone and hydrogen permeation, thereby inhibiting the initiation and propagation of fatigue cracks.

Influence of Plasma Electrolytic Oxidation on Fatigue Behaviour of ZK60A-T5 Magnesium Alloy

Magnesium alloys are used in the motorsport and aerospace fields because of their high specific strength. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating, are necessary when they are used in humid or corrosive environments. The present study aimed at evaluating the effect of plasma electrolytic oxidation (PEO), followed by the deposition of a polymeric layer by powder coating, on the rotating bending fatigue behaviour of the wrought magnesium alloy ZK60A-T5. The specimens were extracted from forged wheels of racing motorbikes and were PEO treated and powder coated. Microstructural characterization was carried out by optical (OM) and scanning electron microscopy (SEM) to analyse both the bulk material and the multilayer, consisting of the anodic oxide interlayer with the powder coating top layer (about 40 µm total thickness). Rotating bending fatigue tests were carried out to obtain the S–N curve of PEO-treated specimens. The results of the rotating bending tests evidenced fatigue strength equal to 104 MPa at 106 cycles and 90 MPa at 107 cycles. The results of the investigation pointed out that PEO led to a reduction in fatigue strength between 14% and 17% in comparison to the untreated alloy. Fracture surface analyses of the fatigue specimens, carried out by SEM and by 3D digital microscopy, highlighted multiple crack initiation sites at the interface between the PEO layer and substrate, induced by the concurrent effects of coating defects, local tensile stresses in the substrate, and increased roughness at the substrate–coating interface.

Plasma Electrolytic Oxidation of Titanium Alloys To Protect Adjacent Aluminum Alloys Element from Contact Corrosion

The plasma electrolytic oxidation of the titanium alloy OT4 was studied; the characteristics of the resulting coatings were determined–thickness, breakdown potential, corrosion current density, and X-ray phase; micro-X-ray spectral analysis was performed, and the morphology of the coatings was studied by scanning electron microscopy. We studied the effect of plasma electrolytic oxidation of OT4 and additional treatment of PEO coatings on the corrosion resistance of the aluminum alloy D16 (An.Ox.nchr, anodic treatment in chromate solutions) in contact with the titanium alloy in structurally similar samples.

On the effect of plasma electrolytic oxidation on the fatigue strength of V96Ts1 (Al-Zn-Mg-Cu) aluminum alloy

One of the tasks of modern material science is to obtain new functional high-strength resistant coatings on structural materials like aluminum alloys. This paper shows the effect of plasma electrolytic oxidation (PEO) on the fatigue strength of V96Ts1 (Al-Zn-Mg-Cu) aluminum alloy. Fatigue tests were carried out with uniaxial loading in accordance with the harmonic law with a constant stress of 205 MPa. The modification of the PEO-coated surface layer led to a 5-fold decrease in the cyclic durability of the V96Ts1 alloy. The dependencies of the temperature of dissipative heating and the accumulated strain on the amplitude of the effective load were obtained for the inelastic cyclic strain of V96Ts alloy samples, with and without a PEO-coated surface layer. These dependencies describing material degradation correlate with the data of the fatigue tests. A fractographic analysis of the destroyed samples was also performed.

Plasma Electrolytic Oxidation as a Feasible Surface Treatment for Biomedical Applications: an in vivo study

Objectives: In this in vivo animal study, we evaluated the effect of plasma electrolytic oxidation (PEO) coating on the topographic and biological parameters of implants installed in rats with induced osteoporosis and low-quality bones. Materials and methods: In total 44 Wistar rats (Rattus novergicus), 6 months old, were submitted to ovariectomy (OXV group) and dummy surgery (SHAM group). After 90 days, the ELISA test was performed and the ovariectomy effectiveness was confirmed. In each tibial metaphysis, an implant with PEO coating containing Ca2+ and P5+ molecules were installed, and the other tibia received an implant with SLA acid etching and blasting (AC) (control surface). After 42 days, 16 rats from each group were euthanized, their tibias were removed for histological and immunohistochemical analysis (OPG, RANKL, OC and TRAP), as well as reverse torque biomechanics. Data were submitted to One-way ANOVA or Kruskal-Wallis tests, followed by a Tukey post-test; P < 0.05. Histological analyses showed higher bone neoformation values among the members of the PEO group, SHAM and OVX groups. Immunohistochemical analysis demonstrated equilibrium in all groups when comparing surfaces for TRAP, OC and RANKL (P > 0.05), whereas OPG showed higher PEO labeling in the OVX group (P < 0.05). Biomechanical analysis showed higher reverse torque values (N.cm) for PEO, irrespective of whether they were OVX or SHAM groups (P < 0.05). Conclusion: The results indicated that the PEO texturing method favored bone formation and showed higher bone maturation levels during later periods in osteoporotic rats.

Improved Electrochemical Performance of Plasma Electrolytic Oxidation Coating on Titanium in Simulated Body Fluid

The effect of plasma electrolytic oxidation (PEO) pre-treatments on corrosion behavior of titanium in simulated body fluid (SBF) is investigated. Three pre-treatments are compared, using silicate, calcium phosphate and mixed silicate and calcium phosphate (1:1) electrolytes, respectively. The resultant coatings in different compositions and morphologies were examined by high-resolution field emission scanning electron microscopy equipped with energy-dispersive spectrometer and x-ray diffraction. The PEO-treated specimens revealed distribution of coating species, mainly the titanium-rich inner coating region. However, findings show highly localized variations in composition within their crystalline structures, due to the melting and rapid solidification of the coating material in three different electrolytes. Corrosion behavior of the coatings was also examined in SBF at 37 °C by potentiodynamic polarization, revealing an improvement in corrosion resistance for mixed electrolyte compared to silicate and calcium phosphate electrolytes.

Influence of PEO and mechanical keying on the strength of AA 5052 alloy/polypropylene friction stir spot welded joints

A study has been carried out of the effect of plasma electrolytic oxidation (PEO) on the strength of AA 5052 alloy/polypropylene joints prepared using friction stir spot welding (FSSW). The joint strengths were determined using lap-shear tests and failure modes were investigated using scanning electron microscopy. Comparisons were made between control joints prepared with the alloy in the as-rolled condition or the as-rolled condition with a mechanical key and with PEO-treated alloy, with or without a mechanical key. Mechanical keying alone, provided by infiltration of polymer into holes of either 3 or 4.5 mm diameter drilled in the alloy, yielded enhancements of the joint strength by a factor of 1.8 and 3.8, respectively, compared with the as-rolled alloy. In contrast, PEO pre-treatment provided a much greater improvement in strength, by a factor of 21.3, with no significant influence of the presence of a mechanical key. The fracture of PEO-treated joints involved a mixture of de-bonding at the polymer/coating interface, cohesive failure within the coating and ductile failure of the polymer. The last resulted from formation of gas bubbles within the polypropylene due to thermal degradation of the polymer during FSSW. In contrast, in the absence of PEO, the fracture path of the as-rolled and also the as-rolled and mechanically keyed joints passed along the alloy/polypropylene interface and through gas bubbles within the polymer. The enhanced strength of the PEO-treated joints resulted from the strong polypropylene/coating bond resulting from flow of molten polymer into the coating porosity.

Fatigue Behavior of the Rare Earth Rich EV31A Mg Alloy: Influence of Plasma Electrolytic Oxidation

Rare earth rich magnesium alloys are used in aerospace and automotive fields because of their high specific strength and good castability. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating are necessary, when they have to be used in humid or corrosive environments. The present study was aimed at evaluating the effect of plasma electrolytic oxidation (PEO) and different surface roughness (Ra ≈ 0.8 μm and Ra ≈ 0.3 μm) on the rotating bending fatigue of an innovative Mg alloy, with a high content of Nd (up to 3.1 wt %) and Gd (up to 1.7 wt %). Fatigue tests revealed a 15% decrease in the fatigue strength of the PEO-treated alloy (fatigue strength = 88 MPa) with respect to the bare alloy (fatigue strength = 103 MPa). The reduction of fatigue strength was mainly due to the residual tensile stresses induced by the PEO treatment. The effect of surface roughness on the bare alloy was, instead, negligible. The mechanisms of crack initiation were similar in the untreated and PEO-treated alloy, with crack nucleation sites located in correspondence to large facets of the cleavage planes.

Effects of plasma electrolytic oxidation process on the mechanical properties of additively manufactured porous biomaterials

Metallic porous biomaterials are recently attracting more attention thanks to the additive manufacturing techniques which help produce more complex structures as compared to conventional techniques. On the other hand, bio-functional surfaces on metallic biomaterials such as titanium and its alloys are necessary to enhance the biological interactions with the host tissue. This study discusses the effect of plasma electrolytic oxidation (PEO), as a surface modification technique to produce bio-functional layers, on the mechanical properties of additively manufactured Ti6Al4V scaffolds based on the cubic unit cell. For this purpose, the PEO process with two different oxidation times was applied on scaffolds with four different values of relative density. The effects of the PEO process were studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), optical microscopy as well as static and dynamic (fatigue) mechanical testing under compression. SEM results indicated pore formation on the surface of the scaffolds after oxidation with a thickness of 4.85±0.36μm of the oxide layer after 2min and 9.04±2.27μm after 5min oxidation (based on optical images). The static test results showed the high effect of relative density of porous structure on its mechanical properties. However, oxidation did not influence most of the mechanical properties such as maximum stress, yield stress, plateau stress, and energy absorption, although its effect on the elastic modulus was considerable. Under fatigue loading, none of the scaffolds failed even after 106 loading cycles at 70% of their yield stress.

Surface modification of severe plastically deformed ultrafine grained pure titanium by plasma electrolytic oxidation

Severe plastic deformation is the best method for processing ultrafine grained (UFG) high strength commercially pure titanium (CP Ti) without any toxic and harmful elements for biomedical implants. Besides, because of the vital importance of the surface bioactivity of a medical implant, this paper studies the effect of Plasma electrolytic oxidation (PEO) process of UFG CP Ti processed by equal channel angular pressing (ECAP). The aqueous electrolyte chosen for PEO process was prepared by mixing 0.15M calcium acetate hydrate and 0.075M sodium hypophosphite hydrate at a ratio of 1:1wt%. The results showed that in PEO-coated coarse-grained (CG) CP Ti, the dominant components are oxygen and titanium, while the two principal elements in the coating of UFG CP Ti are oxygen and calcium. It was revealed from EDS and X-ray diffractometry analysis that the more HA and higher content of Ca and P is formed on the UFG Ti coated sample in comparison with those on coarse-grained Ti coated. The overall Ca/P ratio in the layer was determined as 1.65 and 1.70 for the cases of CG CP Ti and UFG CP Ti, respectively. Also, a few numbers of microcracks were obtained on the PEO-coated UFG CP Ti sample compared to those in PEO-coated CG CP Ti. The microhardness of PEO-coated UFG CP Ti was 3275MPa which was noticeably higher than the microhardness of UFG CP Ti. The electrochemical impedance spectroscopy (EIS) tests were carried out at room temperature using Ringer's solution. EIS test results indicated that the corrosion resistance of PEO-coated UFG CP Ti was greater than non-coated CP Ti and UFG CP Ti. Furthermore, the PEO-coated UFG CP Ti showed more protection against corrosion compared to PEO-coated CG CP Ti. Finally, it is very promising that UFG Ti with PEO surface modification would be a suitable candidate for replacement of Ti-6Al-4V alloy implants containing toxic elements of Al and V.

Evaluation of La containing PEO pretreatment on protective performance of epoxy coating on magnesium

Abstract The effect of plasma electrolytic oxidation (PEO) process was studied on magnesium surface preparation for epoxy coating implementation. In addition, the effect of lanthanum nitrate, current density, and process time was studied on the microstructure of the prepared oxide coating surface. Epoxy coating was applied on the substrate prepared by PEO using the electrostatic method. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to study the composition and morphology of PEO coatings, as well as the cross-section of the double-layer coatings. The protective performance of the coatings was evaluated using an electrochemical impedance spectroscopy (EIS) test for 28 days in a 3.5% NaCl solution. Finally, the Pull-off adhesion test was carried out to examine the impact of surface preparation in the improvement of the adhesion strength of the organic coatings. Based on the SEM micrographs, the density of PEO coating increases by adding lanthanum nitrate. Furthermore, the results indicate that preparation of magnesium surface by PEO process contributes to protecting organic coating placed 28 days in the corrosive solution without causing any localized corrosion at the interface of organic coating with PEO coatings.

Effect of plasma electrolytic oxidation on joining of AA 5052 aluminium alloy to polypropylene using friction stir spot welding

The effect of a plasma electrolytic oxidation (PEO) pre-treatment on joining of AA 5052 aluminium alloy and polypropylene by friction stir spot welding (FSSW) is investigated using lap tensile shear tests. Two surface conditions of the AA 5052 alloy are compared, one with a PEO pre-treatment in a silicate-based electrolyte, another without any pre-treatment. The resultant specimens are examined by high resolution scanning electron microscopy, thermogravimetric analysis and attenuated total reflectance-infrared spectroscopy. The PEO treatment generated a thermally-insulating, porous ceramic coating, which has a highly porous, rough surface that is favourable for incorporating polypropylene melted by FSSW. The pre-treatment significantly increased the lap tensile shear strength, by about a factor of three, in comparison with the untreated alloy, suggesting that open pores in the coating filled by polypropylene provide strong micromechanical interlocking and covalent bonding between the coated alloy and the polymer.

Role of PEO coatings in long-term biodegradation of a Mg alloy

Long-term effect of plasma electrolytic oxidation (PEO) coatings on in vitro corrosion of 3D Mg implant specimens has been investigated in simulated body fluid (SBF). Hydrogen evolution rate in PEO-coated specimens was 35 times lower compared to the non-coated alloy during first 2 weeks of immersion (0.04–0.07mLcm−2d−1) and reached a steady-state rate of 0.3mLcm−2d−1 by week 6 of immersion. Studies of the tribocorrosion behaviour of the PEO-coated alloy disclosed that the coatings rapidly lose their tribocorrosion resistance due to hydration of the coating material and associated drastic decrease of microhardness but exhibit a better tirbocorrosion performance than the non-coated material.

Effect of plasma electrolytic oxidation treatment on the mechanical properties of a Zr–Cu–Ni–Ti–Al bulk metallic glass

In this study, the effect of plasma electrolytic oxidation (PEO) treatment on the mechanical properties of a Zr52.5Cu25Ni9.5Ti6Al7 BMG was investigated by compression test. It was found that the PEO treatment can improve the room-temperature plasticity. After 30min treatment, the plastic strain of BMG increases from 2.5% to 6.2%. The results indicated that the in-situ formed PEO coating can not only act as physical constraint to consume the kinetic energy of the propagating shear band, but also can introduce nucleation sites for shear bands due to stress concentration and compositional inhomogeneity. The present results provide a promising method to enhance the plasticity of BMGs through surface PEO treatment.

The effect of plasma electrolytic oxidation on the mean stress sensitivity of the fatigue life of the 6082 aluminum alloy

In this work the mean stress influence on the high cycle fatigue behavior of the plasma electrolytic oxidized (PEO) 6082 aluminum alloy (AlSi1MgMn) is investigated. The present study is focused on the fatigue life time and the susceptibility of fatigue-induced cracking of the oxide coating and their dependence on the applied mean stress. Systematic work is done comparing conditions with and without PEO treatment, which have been tested using three different load ratios. For the uncoated substrate the cycles to failure show a significant dependence on the mean stress, which is typical for aluminum alloys. With increased load ratio and therefore increased mean stress, the fatigue strength decreases. The investigation confirms the well-known effect of PEO treatment on the fatigue life: The fatigue strength is significantly reduced by the PEO process, compared to the uncoated substrate. However, also the mean stress sensitivity of the fatigue performance is reduced. The fatigue limit is not influenced by an increasing mean stress for the PEO treated conditions. This effect is firstly shown in these findings and no explanation for this effect can be found in literature. Supposedly the internal compressive stresses and the micro-cracks in the oxide film have a direct influence on the crack initiation and growth from the oxide film through the interface and in the substrate. Contrary to these findings, the susceptibility of fatigue-induced cracking of the oxide coating is influenced by the load ratio. At tension-tension loading a large number of cracks, which grow partially just in the aluminum substrate, are present. With decreasing load ratio to alternating tension-compression stresses, the crack number and length increases and shattering of the oxide film is more pronounced due to the additional effective compressive part of the load cycle.

Influence of coating morphology on adhesive bonding of titanium pre-treated by plasma electrolytic oxidation

Abstract The effect of plasma electrolytic oxidation (PEO) pre-treatments on the adhesive bonding of titanium is investigated using lap-shear tests. Two pre-treatments are compared, using aluminate-phosphate and silicate-phosphate electrolytes respectively, which result in different compositions and morphologies of coatings. Specimens were joined with an epoxy adhesive. The PEO-treated specimens revealed mainly cohesive failure within the titanium-rich inner coating regions, which contrasted with the adhesive failure of untreated titanium. The silicate-phosphate pre-treatment resulted in the infiltration of a highly porous outer region of the coating by the adhesive. The fracture of the coatings occurred close to the titanium/coating interface and intersected the bases of relatively large pores, which in the case of the aluminate-phosphate coating lay beneath nodules that were evident at the coating surface. The pre-treatments did not significantly increase the lap-shear strength in comparison with untreated titanium.

In vitro bioactivity investigations of Ti-15Mo alloy after electrochemical surface modification.

Titanium and its aluminum and vanadium-free alloys have especially great potential for medical applications. Electrochemical surface modification improves their surface bioactivity and stimulates osseointegration process. In this work, the effect of plasma electrolytic oxidation of the β-type alloy Ti-15Mo surface on its bioactivity is presented. Bioactivity of the modified alloy was investigated by immersion in simulated body fluid (SBF). Biocompatibility of the modified alloys were tested using human bone marrow stromal cells (hBMSC) and wild intestinal strains (DV/A, DV/B, DV/I/1) of Desulfovibrio desulfuricans bacteria. The particles of apatite were formed on the anodized samples. Human BMSC cells adhered well on all the examined surfaces and expressed ALP, collagen, and produced mineralized matrix as determined after 10 and 21 days of culture. When the samples were inoculated with D. desulfuricans bacteria, only single bacteria were visible on selected samples. There were no obvious changes in surface morphology among samples. Colonization and bacterial biofilm formation was observed on as-ground sample. In conclusion, the surface modification improved the Ti-15Mo alloy bioactivity and biocompatibility and protected surface against colonization of the bacteria. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 903-913, 2016.

Effect of plasma electrolytic oxidation coating on joining metal to plastic

Joining of magnesium alloy to polyethylene without adhesive using a newly developed friction lap welding technology was investigated. The polyethylene and magnesium alloy were hard to be joined together without surface premodification due to the lack of polar groups on polyethylene surfaces. Strong hybrid joints were achieved after the polyethylene was treated by corona discharge, and the magnesium alloy was subjected to plasma electrolytic oxidation treatment. Scanning electron microscope and high resolution transmission electron microscope observations demonstrated that the high joining strength was attributed to the development of both chemical bonds at the interface and micromechanical interlocking.