Micro-structures and growth mechanisms of plasma electrolytic oxidation coatings on aluminium at different current densities

Zhang, Yi; Wu, Ye‐kang; Chen, Dong; Wang, Rui-Qiang; Li, Dalong; Guo, Changhong; Jiang, Guirong; Shen, Dejiu; Yu, Sirong; Nash, Philip

doi:10.1016/j.surfcoat.2017.04.064

Cited by 71 publications

(28 citation statements)

References 48 publications

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“…The outer layers are denser than the highly porous intermediate layers. This might be due to solidification and oxidation of the molten substrate ejected from underneath the forming porous oxide during the PEO [ 24 , 25 , 26 ]. This intermediate sublayer was especially thin for the Ca1P2 400 V sample ( Figure 2 c), when compared with those obtained from the Ca5P3 ( Figure 2 f) and (CaMg)5P3 ( Figure 2 i) electrolytes.…”

Section: Resultsmentioning

confidence: 99%

Electrochemical Impedance and Polarization Corrosion Studies of Tantalum Surface Modified by DC Plasma Electrolytic Oxidation

Sowa

Simka

2018

Materials

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Tantalum has recently become an actively researched biomaterial for the bone reconstruction applications because of its excellent corrosion resistance and successful clinical records. However, a bare Ta surface is not capable of directly bonding to the bone upon implantation and requires some method of bioactivation. In this study, this was realized by direct current (DC) plasma electrolytic oxidation (PEO). Susceptibility to corrosion is a major factor determining the service-life of an implant. Therefore, herein, the corrosion resistance of the PEO coatings on Ta was investigated in Ringer’s solution. The coatings were formed by galvanostatic anodization up to 200, 300 and 400 V, after which the treatment was conducted potentiostatically until the total process time amounted to 5 min. Three solutions containing Ca(H2PO2)2, Ca(HCOO)2 and Mg(CH3COO)2 were used in the treatment. For the corrosion characterization, electrochemical impedance spectroscopy and potentiodynamic polarization techniques were chosen. The coatings showed the best corrosion resistance at voltages low enough so that the intensive sparking was absent, which resulted in the formation of thin films. The impedance data were fitted to the equivalent electrical circuits with two time constants, namely R(Q[R(QR)]) and R(Q[R(Q[RW])]). The inclusion of W in the circuit helped to fit the low-frequency part of the samples PEO-ed at 400 V, hinting at the important role of diffusion in the corrosion resistance of the PEO coatings described in the research.

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Section: Resultsmentioning

confidence: 99%

Electrochemical Impedance and Polarization Corrosion Studies of Tantalum Surface Modified by DC Plasma Electrolytic Oxidation

Sowa

Simka

2018

Materials

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“…The strong discharge with a subsequent current drop resulted in the growth of a dielectric porous outer layer 6.86 ± 1.03 µm in thickness 22 . According to Zhang et al 23 , during the formation of the outer porous layer a much lower voltage drop occurs than when the inner layer is forming. This can be explained by the much lower resistance of the outer porous layer in comparison with the compact inner layer.…”

Section: Resultsmentioning

confidence: 99%

Preparation of highly wettable coatings on Ti–6Al–4V ELI alloy for traumatological implants using micro-arc oxidation in an alkaline electrolyte

Gabor

Doubková

Gorosova

et al. 2020

Sci Rep

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Pulsed micro-arc oxidation (MAO) in a strongly alkaline electrolyte (pH > 13), consisting of Na2SiO3⋅9H2O and NaOH, was used to form a thin porous oxide coating consisting of two layers differing in chemical and phase composition. The unique procedure, combining MAO and removal of the outer layer by blasting, enables to prepare a coating suitable for application in temporary traumatological implants. A bilayer formed in an alkaline electrolyte environment during the application of MAO enables the formation of a wear-resistant layer with silicon incorporated in the oxide phase. Following the removal of the outer rutile-containing porous layer, the required coating properties for traumatological applications were determined. The prepared surfaces were characterized by scanning electron microscopy, X-ray diffraction patterns, X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements. Cytocompatibility was evaluated using human osteoblast-like Saos-2 cells. The newly-developed surface modifications of Ti–6Al–4V ELI alloy performed satisfactorily in all cellular tests in comparison with MAO-untreated alloy and standard tissue culture plastic. High cell viability was supported, but the modifications allowed only relatively slow cell proliferation, and showed only moderate osseointegration potential without significant support for matrix mineralization. Materials with these properties are promising for utilization in temporary traumatological implants.

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“…From reference [ 39 ], a passivation layer with a thickness of 6–20 nm can be formed on the exposed silicon crystals via chemisorption. A natural oxide layer on aluminium matrix, which is composed of amorphous Al 2 O 3 with a thickness of 2–3 nm, also exists before passivation [ 6 , 41 , 42 ]. In the passivation stage, both of them will grow thicker and reach 10–15 nm by anodizing oxidation, as shown in figure 7 a .…”

Section: Discussionmentioning

confidence: 99%

Influence of silicon on growth mechanism of micro-arc oxidation coating on cast Al–Si alloy

Dong

Yang

et al. 2018

R. Soc. open sci.

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Micro-arc oxidation (MAO) is a plasma-assisted electrochemistry method to prepare protective ceramic coatings on aluminium alloys. Alloy elements of the Al-alloy substrate, such as Si, Cu, Mg and Li, have effects on the microstructure and composition of the MAO coatings. Usually, silicon distributes in the cast Al–Si alloy substrate as small laths and they cover approximately 10% of the substrate surface. Therefore, their effects on the growth process and microstructure of the MAO coatings are worthy of notice. In the present study, oxide coatings with a thickness of 15–18 µm were prepared on the ZL109 Al–Si alloy by MAO. The phase content, surface morphology and element distribution of the coatings were investigated by X-ray diffraction, grazing incidence X-ray diffraction, scanning electron microscope, and electron probe micro-analysis respectively. The average hardness of the coatings was 622.3 ± 10.2 HV0.05. The adhesive strength of the coatings is 40.55 ± 2.55 N, and the adhesion of the coatings could be rated as 5B by tape test according to ASTM D3359-17 standard test methods, which indicated a high adhesive strength between the MAO coating and substrate. The effects of silicon laths on surface morphology and composition of the coatings were discussed, and a model was put forward to describe the growth process of the MAO coatings on cast Al–Si alloys. The authors believe that the high silicon content of the substrate has no adverse influence on the structure and properties of the MAO coating on the ZL109 alloy.

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Micro-structures and growth mechanisms of plasma electrolytic oxidation coatings on aluminium at different current densities

Cited by 71 publications

References 48 publications

Electrochemical Impedance and Polarization Corrosion Studies of Tantalum Surface Modified by DC Plasma Electrolytic Oxidation

Electrochemical Impedance and Polarization Corrosion Studies of Tantalum Surface Modified by DC Plasma Electrolytic Oxidation

Preparation of highly wettable coatings on Ti–6Al–4V ELI alloy for traumatological implants using micro-arc oxidation in an alkaline electrolyte

Influence of silicon on growth mechanism of micro-arc oxidation coating on cast Al–Si alloy

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