Evolution process of the plasma electrolytic oxidation (PEO) coating formed on aluminum in an alkaline sodium hexametaphosphate ((NaPO3)6) electrolyte

Wang, Dongdong; Liu, Xintong; Wu, Ye‐kang; Han, Huiping; Yang, Zhong; Su, Yu; Zhang, Xuzhen; Wu, Guo-rui; Shen, Dejiu

doi:10.1016/j.jallcom.2019.05.253

Cited by 73 publications

(27 citation statements)

References 57 publications

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“…By the increase of SMS concentration, most of the pancakes are covered by the nodules. This confirms that the nodules are majorly formed by the participation of solution constituents through interfacial micro-discharges [33].…”

Section: Koh Effect On Voltage-time Responsesupporting

confidence: 74%

Silicate and Hydroxide Concentration Influencing the Properties of Composite Al2O3-TiO2 PEO Coatings on AA7075 Alloy

et al. 2021

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This work evaluates the effect of sodium meta-silicate pentahydrate (SMS) and potassium hydroxide concentrations on properties of Al2O3-TiO2 coatings produced through plasma electrolytic oxidation in a solution containing 3 g L−1 potassium titanyl oxalate, (PTO), using a unipolar waveform with constant current density. The surface and cross-section characteristics of PEO coatings including morphology, elemental distribution, and phase composition were evaluated using FESEM, EDS, and XRD techniques. Voltage-time response indicated the concentration of SMS and KOH had a significant effect on the duration of each stage of the PEO process. More cracks and pores were formed at the higher concentrated solutions that resulted in the incorporation of solution components especially Si into the coating inner parts. Ti is distributed throughout the coatings, but it had a dominant distribution in the Si-rich areas. The coating prepared in the electrolyte containing no silicate consisted of non-stoichiometric γ-Al2O3 and/or amorphous Al2O3 phase. Adding silicate into the coating electrolyte resulted in the appearance of α-Al2O3 besides the dominant phase of γ-Al2O3. The corrosion behaviour of the coatings was investigated using the EIS technique. It was found that the coating prepared in the presence of 3 g L−1 SMS and 2 g L−1 KOH, possessed the highest barrier resistance (~10 MΩ cm2), owing to a more compact outer layer, thicker inner layer along with appropriate dielectric property because this layer lacks the Si element. It was discovered that the incorporation of Ti4+ and especially Si4+ in the coating makes the dielectric loss in the coating.

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Section: Koh Effect On Voltage-time Responsesupporting

confidence: 74%

Silicate and Hydroxide Concentration Influencing the Properties of Composite Al2O3-TiO2 PEO Coatings on AA7075 Alloy

et al. 2021

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“…Moreover, the different mechanisms of the coating formation indicated by the crystal structures can be obtained directly after the anodization process of other metals, such as zirconium, where the crystal form of ZrO 2 anodic oxide is observed [ 23 ]. In addition, the possibility of crystalline oxide formation was observed for technical grade aluminum anodized using the plasma electrolytic oxidation (PEO) technique [ 24 ]. As a result, two crystalline allotropic forms of aluminum oxide were obtained, namely, high-temperature α-Al 2 O 3 [ 24 ], which has a high heat resistance, and hexagonal γ-Al 2 O 3 [ 24 , 25 ], which has a relatively large specific surface and can be used as an adsorbent [ 26 ] or a catalyst carrier [ 27 ].…”

Section: Resultsmentioning

confidence: 99%

“…In addition, the possibility of crystalline oxide formation was observed for technical grade aluminum anodized using the plasma electrolytic oxidation (PEO) technique [ 24 ]. As a result, two crystalline allotropic forms of aluminum oxide were obtained, namely, high-temperature α-Al 2 O 3 [ 24 ], which has a high heat resistance, and hexagonal γ-Al 2 O 3 [ 24 , 25 ], which has a relatively large specific surface and can be used as an adsorbent [ 26 ] or a catalyst carrier [ 27 ]. It is interesting that the described mechanism of the formation of the anodic alumina oxide layer as a result of the PEO process is similar to that observed during the anodization of FeAl 3 , as presented in this paper.…”

Section: Resultsmentioning

confidence: 99%

Nanoporous Anodic Aluminum-Iron Oxide with a Tunable Band Gap Formed on the FeAl3 Intermetallic Phase

2020

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Nanostructured anodic oxide layers on an FeAl3 intermetallic alloy was prepared by two-step anodization in 20 wt.% H2SO4 at 0 °C. The obtained anodic oxide coating was subjected to phase and chemical composition analysis using XPS and XRD techniques. An analysis of the band gap of individual coatings was also performed. The applied parameters of the anodization process were determined, enabling the formation of a nanostructured coating on the FeAl3 intermetallic alloy. Tests were carried out on samples produced at a voltage between 10 V and 22.5 V in 2.5 V steps. The produced coatings were subjected to an annealing process at 900 °C for 2 h in an argon protective atmosphere. Moreover, the influence of the substrate chemical composition on the chemical and phase composition of the anodic oxide are discussed. Band gaps of 2.37 eV at 22.5 V and 2.64 eV at 10 V were obtained directly after the anodizing process. After applying the heat treatment, band gap values of 2.10 eV at 22.5 Vand 2.48 eV for the coating produced at 10 V were obtained.

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“…The electrolyte component plays a critical role, affecting the surface composition, morphology, structure, and properties of PEO coatings. Generally, the PEO electrolytes are alkaline silicate [15], phosphate [16], and aluminate solutions [17], according to their main components. Many works reported that the PEO coatings prepared from silicate electrolyte were composed of silica, alumina, and mullite [18][19][20][21][22].…”

Section: Experimental Details 21 Peo Processmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Wear and Corrosion Resistance of Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Electrolytes with Aluminate and Phosphate

Peng

Liu

et al. 2021

Materials

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Phosphate and aluminate electrolytes were used to prepare plasma electrolytic oxidation (PEO) coatings on 6061 aluminum alloy. The surface and cross-section microstructure, element distribution, and phase composition of the PEO coatings were characterized by SEM, EDS, XPS, and XRD. The friction and wear properties were evaluated by pin-on-disk sliding tests under dry conditions. The corrosion resistance of PEO coatings was investigated by electrochemical corrosion and salt spray tests in acidic environments. It was found that the PEO coatings prepared from both phosphate and aluminate electrolytes were mainly composed of α-Al2O3 and γ-Al2O3. The results demonstrate that a bi-layer coating is formed in the phosphate electrolyte, and a single-layered dense alumina coating with a hardness of 1300 HV is realizable in the aluminate electrolyte. The aluminate PEO coating had a lower wear rate than the phosphate PEO coating. However, the phosphate PEO coating showed a better corrosion resistance in acidic environment, which is mainly attributed to the presence of an amorphous P element at the substrate/coating interface.

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Evolution process of the plasma electrolytic oxidation (PEO) coating formed on aluminum in an alkaline sodium hexametaphosphate ((NaPO3)6) electrolyte

Cited by 73 publications

References 57 publications

Silicate and Hydroxide Concentration Influencing the Properties of Composite Al2O3-TiO2 PEO Coatings on AA7075 Alloy

Silicate and Hydroxide Concentration Influencing the Properties of Composite Al2O3-TiO2 PEO Coatings on AA7075 Alloy

Nanoporous Anodic Aluminum-Iron Oxide with a Tunable Band Gap Formed on the FeAl3 Intermetallic Phase

Wear and Corrosion Resistance of Plasma Electrolytic Oxidation Coatings on 6061 Al Alloy in Electrolytes with Aluminate and Phosphate

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