• Journal of Electrical Engineering and Technology
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• 제10권4호
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• pp.1746-1751
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• 2015

In this study low voltage Plasma Electrolytic Oxidation (PEO) was utilized to eliminate high voltage PEO drawbacks such as high cost, dimensional deformation and porosity. Low voltage PEO produces a thin coating which causes low corrosion resistance. In order to solve such problem, 0.1~0.6M pyrophosphates were added in a bath containing 1.4M NaOH, and 0.35M Na₂SiO₃. 70 V PEO was conducted at 25℃ for 3 minutes. Chemical composition, morphology and corrosion resistance of the anodized coating were analyzed. The anodized film was composed of MgO, Mg₂SiO₄, and Mg₂O₇P₂. The morphology of film showed appropriately dense structure and low porosity in the anodized layers. It is found that low voltage Plasma Electrolytic Oxidation in cooperation with phosphating treatment can provide a good corrosion protection for the AZ31B magnesium alloy.

• Corrosion Science and Technology
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• 제17권3호
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• pp.91-100
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• 2018

Development of biodegradable implants for treatment of complex bone fractures has recently become one of the priority areas in biomedical materials research. Multifunctional corrosion resistant and bioactive coatings containing hydroxyapatite $Ca_{10}(PO_4)_6(OH)_2$ and magnesium oxide MgO were obtained on Mg-Mn-Ce magnesium alloy by plasma electrolytic oxidation. The phase and elemental composition, morphology, and anticorrosion properties of the coatings were investigated by scanning electron microscopy, energy dispersive spectroscopy, potentiodynamic polarization, and electrochemical impedance spectroscopy. The PEO-layers were post-treated using superdispersed polytetrafluoroethylene powder. The duplex treatment considerably reduced the corrosion rate (>4 orders of magnitude) of the magnesium alloy. The use of composite coatings in inducing bioactivity and controlling the corrosion degradation of resorbable Mg implants are considered promising. We also applied the plasma electrolytic oxidation method for the formation of the composite bioinert coatings on the titanium nickelide surface in order to improve its electrochemical properties and to change the morphological structure. It was shown that formed coatings significantly reduced the quantity of nickel ions released into the organism.

• 한국표면공학회지
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• 제49권2호
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• pp.119-124
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• 2016

Plasma electrolytic oxidation (PEO) is a promising coating process to produce ceramic oxide on valve metals such as Al, Mg and Ti. The PEO coating is carried out with a dilute alkaline electrolyte solution using a similar technique to conventional anodizing. The coating process involves multiple process parameters which can influence the surface properties of the resultant coating, including power mode, electrolyte solution, substrate, and process time. In this study, ceramic oxide coatings were prepared on commercial Al alloy in electrolytes with different KOH concentrations (0.5 ~ 4 g/L) by plasma electrolytic oxidation. Microstructural and electrochemical characterization were conducted to investigate the effects of electrolyte concentration on the microstructure and electrochemical characteristics of PEO coating. It was revealed that KOH concentration exert a great influence not only on voltage-time responses during PEO process but also on surface morphology of the coating. In the voltage-time response, the dielectric breakdown voltage tended to decrease with increasing KOH concentration, possibly due to difference in solution conductivity. The surface morphology was pancake-like with lower KOH concentration, while a mixed form of reticulate and pancake structures was observed for higher KOH concentration. The KOH concentration was found to have little effect on the electrochemical characteristics of coating, although PEO treatment improved the corrosion resistance of the substrate material significantly.

• 한국재료학회지
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• 제27권9호
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• pp.495-500
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• 2017

Oxide layers were formed by an environmentally friendly plasma electrolytic oxidation (PEO) process on AZ91 Mg alloy. PEO treatment also resulted in strong adhesion between the oxide layer and the substrate. The influence of the KF electrolytic solution and the structure, composition, microstructure, and micro-hardness properties of the oxide layer were investigated. It was found that the addition of KF instead of KOH to the $Na_2SiO_3$ electrolytic solution increased the electrical conductivity. The oxide layers were mainly composed of MgO and $Mg_2SiO_4$ phases. The oxide layers exhibited solidification particles and pancake-shaped oxide melting. The pore size and surface roughness of the oxide layer decreased considerably with an increase in the concentration of KF, while densification of the oxide layers increased. It is shown that the addition of KF to the basis electrolyte resulted in fabricating of an oxide layer with higher surface hardness and smoother surface roughness on Mg alloys by the PEO process. The uniform thickness of the oxide layer formed on the Mg alloy substrates was largely determined by the electrolytic solution with KF, which suggests that the composition of the electrolytic solution is one of the key factors controlling the uniform thickness of the oxide layer.

• 한국세라믹학회지
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• 제46권3호
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• pp.295-300
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• 2009

The crystal structure of surface coatings on Al1050 alloy by PEO (Plasma Electrolytic Oxidation), were investigated. The electrolyte for PEO was Na-Si-P system solution. The main crystalline phase were $\gamma$-alumina and $\alpha$-alumina. Crystallinity was increased with applied voltage and applied time. The dominant crystalline phase were affected not only chemical composition of Al alloy substrate and electrolyte, but also the +/- ratio of applied voltage.

• Corrosion Science and Technology
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• 제5권6호
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• pp.213-217
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• 2006

Titania coatings were prepared on commercially pure Ti by plasma electrolytic oxidation (PEO) method with various electrolytes and process condition. Coatings were formed under galvanostatic condition with several current density values, and the change of applied voltage with process time was recorded. The microstructure of the titania coatings was observed using XRD, SEM, TEM, and the time-voltage diagrams were analyzed in terms of microstructure evolution.

• 열처리공학회지
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• 제25권5호
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• pp.227-232
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• 2012

Magnesium alloy have good physical properties such as good castability, good vibration absorption, high strength/weight ratios. Despite the desirable properties, the poor resistance of Mg alloy impedes their use in many various applications. Therefore, magnesium alloy require surface treatment to improve hardness, corrosion and wear resistance. Plasma Electrolytic Oxidation (PEO) is one the surface treatment methods to form oxide layer on Mg alloy in alkali electrolyte. In comparison with Anodizing, there is environmental process having higher hardness and faster deposition rate. In this study, the characteristics of oxide film were examined after coating the AZ31 Mg alloy through the PEO process. We changed concentration of sodium aluminate into $K_2ZrF_6$, KF base electrolyte. The morphologies of the coating layer were characterized by using scanning electron microscopy (SEM). Corrosion resistance also investigated by potentiodynamic polarization analysis. As a result, propertiy of oxide layer were changed by concentration of sodium aluminate. Increasing with concentration of sodium aluminate in electrolyte, the oxidation layer was denser and the pore size was smaller on the surface.

• 한국주조공학회지
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• 제28권1호
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• pp.20-24
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• 2008

The characteristics, such as roughness, thickness, microhardness and corrosion resistance, of plasma electrolytic oxide coatings on AZ91D alloy were investigated under the processing condition of various coating times. The coatings on AZ91D alloy consisted of MgO, $MgAl_{2}O_{4}$ and $Mg_{2}SiO_{4}$ oxides. The surface roughness and thickness of coatings became larger with increasing the coating time. The microhardness in cross section of coatings was much higher than not only that in surface but that in the conventional anodic oxide coatings, which increased progressively as the coating time increased. After being immersed in 3.5%NaCl solution and methyl alcohol, the corrosion resistance of AZ91D alloy was markedly improved by plasma electrolytic oxidation coating treatment, and the AZ91D alloy coated for 50min revealed excellent corrosion resistance.

• Corrosion Science and Technology
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• 제22권4호
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• pp.257-264
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• 2023

Ti-6Al-4V alloys are mainly used as dental materials due to their excellent biocompatibility, corrosion resistance, and chemical stability. However, they have a low bioactivity with bioinertness in the body. Therefore, they could not directly bond with human bone. To improve their applications, their bone bonding ability and bone formation capacity should be improved. Thus, the objective of this study was to improve the bioinert surface of titanium alloy substrate to show bioactive characteristics by performing surface modification using wollastonite powder. Commercial bioactive wollastonite powder was successfully deposited onto Ti-6Al-4V alloy using a room temperature spray process. It was found that wollastonite-coated layer showed homogeneous microstructure and uniform thickness. Corrosion resistance of Ti-6Al-4V alloy was also improved by plasma electrolytic oxidation treatment. Its wettability and bioactivity were also greatly increased by wollastonite coating. Results of this study indicate that both plasma electrolytic oxidation treatment and wollastonite coating by room temperature spray process could be used to improve surface bioactivity of Ti-6Al-4V alloy substrate.

• Journal of Welding and Joining
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• 제32권3호
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• pp.27-33
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• 2014

This paper presents a brief summary on a relatively new plasma aided electrolytic surface treatment process for light metals. A brief discussion regarding the advantages, principle, process parameters and applications of this process is discussed. The process owes its origin to Sluginov who discovered an arc discharge phenomenon in electrolysis in 1880. A similar process was studied and developed by Markov and coworkers in 1970s who successfully deposited an oxide film on aluminium. Several investigation thereafter lead to the establishment of suitable process parameters for deposition of a crystalline oxide film of more than $100{\mu}m$ thickness on the surface of light metals such as aluminium, titanium and magnesium. This process nowadays goes by several names such as plasma electrolytic oxidation (PEO), micro-arc oxidation (MOA), anodic spark deposition (ASD) etc. Several startups and surface treatment companies have taken up the process and deployed it successfully in a range of products, from military grade rifles to common off road sprockets. However, there are certain limitations to this technology such as the formation of an outer porous oxide layer, especially in case of magnesium which displays a Piling Bedworth ratio of less than one and thus an inherent non protective oxide. This can be treated further but adds to the cost of the process. Overall, it can be said the PEO process offers a better solution than the conventional coating processes. It offers advantages considering the fact that he electrolyte used in PEO process is environmental friendly and the temperature control is not as strict as in case of other surface treatment processes.