Tailored aluminium oxide layers by bipolar current adjustment in the Plasma Electrolytic Oxidation (PEO) process

Jaspard-Mécuson, F.; Czerwiec, T.; Henrion, G.; Belmonte, T.; Dujardin, Laurence; Viola, A.; Beauvir, J.

doi:10.1016/j.surfcoat.2006.09.005

Cited by 186 publications

(139 citation statements)

References 19 publications

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“…If this process has undeniable assets for surface treatments of light alloys (high growth rate, high ultimate coating thickness, ecofriendliness, wear and corrosion resistance, etc. ), the high energy consumption and the lack of understanding of the fundamental processes underlying the breakdown and the oxidation mechanisms still limit a larger scale development.Improving the energetic efficiency of PEO is a major stake and several strategies can then be followed: dual treatments[1], addition of nanoparticles [2,3], electrolyte composition [4,5] and electric regimes [5][6][7][8]. Here, we focus on the influence of the electric regime as it has a direct and strong influence on both the space and time properties of micro-discharges (MD), which affect the coating growth.…”

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confidence: 99%

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High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

et al. 2017

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The present communication shows the possibility of observing micro-discharges under cathodic polarization during Plasma Electrolytic Oxidation (PEO) at high frequency. Cathodic micro-discharges can ignite beyond a threshold frequency found close to 2 kHz. The presence (resp. absence) of an Electrical Double Layer (EDL) was put forward to explain how the applied voltage can be screened, which therefore prevents (resp. promotes) the ignition of a discharge. Interestingly, in the conditions of the present study, the EDL requires between 175 and 260 µs to form. This situates the expected threshold frequency between 1.92 and 2.86 kHz, which is in good agreement with the value obtained experimentally.Plasma Electrolytic Oxidation (PEO) is at a pivotal moment of its development. If this process has undeniable assets for surface treatments of light alloys (high growth rate, high ultimate coating thickness, ecofriendliness, wear and corrosion resistance, etc.), the high energy consumption and the lack of understanding of the fundamental processes underlying the breakdown and the oxidation mechanisms still limit a larger scale development.Improving the energetic efficiency of PEO is a major stake and several strategies can then be followed: dual treatments[1], addition of nanoparticles [2,3], electrolyte composition [4,5] and electric regimes [5][6][7][8]. Here, we focus on the influence of the electric regime as it has a direct and strong influence on both the space and time properties of micro-discharges (MD), which affect the coating growth. Interestingly, the best properties and the highest growth rates of coatings are obtained while using bipolar current waveform [5,9] even though MDs are only observed during the anodic (i.e. positive) half-period [10][11][12] in these conditions.To explain this observation, one should keep in mind that the growth of PEO coatings relies on a balance between the constructive effect of MDs (oxidation and coating growth) and their destructive effect (large craters and porosities). Several studies conducted either by high speed video imaging [5,6,[11][12][13][14][15][16][17][18] or by direct electrical measurements [10,19] have investigated this balance. They made it possible to correlate space and time parameters of MDs (number, life-time, size) and the properties of as-grown coatings (thickness, porosity). In short, large and long-lived discharges promote the growth of high temperature phases but create large porosities (several tens of µm), high roughness at limited growth rates (strong destructive effect of MDs). On the other hand, too small and short-lived MDs will create more homogeneous coating but with lower amount of high-temperature phases and also at limited growth rates (weak constructive effect).Nevertheless, all these studies support the same conclusion: adjusting the cathodic half period probably opens up the possibility to tune the behaviour of anodic MDs. Then, combining high-growth rates, low levels of large-scale porosity (bigger than 10 µm) and a significant proportio...

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confidence: 99%

“…Several studies conducted either by high speed video imaging [5,6,[11][12][13][14][15][16][17][18] or by direct electrical measurements [10,19] have investigated this balance. They made it possible to correlate space and time parameters of MDs (number, life-time, size) and the properties of as-grown coatings (thickness, porosity).…”

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confidence: 99%

High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

et al. 2017

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“…The lower concentration of oxygen (Fig. 8c) and higher concentration of aluminium ( In PEO of aluminium in alkaline silicate electrolyte, less porous and relatively uniform oxide layer can be formed after transition to "soft" sparking [8,9,12,[15][16][17][18]. The present study reveals that healing open discharge pores occurs more readily during single pulse anodizing in alkaline silicate electrolyte, while such healing is not observed in ammonium pentaborate electrolyte.…”

Section: Methodsmentioning

confidence: 51%

“…It has been recently reported that relatively thick intermediate layer with low porosity is formed between an inner barrier layer and an outer loose layer containing large cavities and pores under selected PEO conditions [8,9,12,[15][16][17][18]. The formation of the intermediate layer is correlated with so called "soft" sparking, which is characterized by a change in the optical emission spectra, reduction in the size of microdischarges and reduction in acoustic noise [16,19]. The importance of cathodic to anodic current ratio is reported to facilitate the formation of less porous intermediate layer [16].…”

Section: Introductionmentioning

confidence: 99%

“…The formation of the intermediate layer is correlated with so called "soft" sparking, which is characterized by a change in the optical emission spectra, reduction in the size of microdischarges and reduction in acoustic noise [16,19]. The importance of cathodic to anodic current ratio is reported to facilitate the formation of less porous intermediate layer [16]. In addition, to our knowledge, such intermediate layer in PEO coatings on aluminium is only formed in alkaline silicate electrolytes.…”

Section: Introductionmentioning

confidence: 99%

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Dielectric breakdown and healing of anodic oxide films on aluminium under single pulse anodizing

et al. 2011

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Single pulse anodizing of aluminium micro-electrode has been employed to study the behaviour of dielectric breakdown and subsequent oxide formation on aluminium in alkaline silicate and pentaborate electrolytes. Current transients during applying pulse voltage have been measured, and surface has been observed by scanning electron microscopy. Two types of current transients are observed, depending on the electrolyte and applied voltage. There is a good correlation between the current transient behaviour and the shape of discharge channels. In alkaline silicate electrolyte, circular open pores are healed by increasing the pulse width, but such healing is not obvious in pentaborate electrolyte.

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Interaction of Discharges in Heptane with Silicon Covered by a Carpet of Carbon Nanotubes

Hamdan

Audinot²,

Migot-Choux

et al. 2013

Adv Eng Mater

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Discharges in heptane in pin-to-plate configuration are produced between a platinum wire and a (100)-oriented silicon wafer coated by a carbon nanotube (CNT) carpet. This carpet is used to simulate the behavior of a nanostructured surface in electro-discharge machining (EDM) where small protrusions on the surface could play a similar role. CNTs behave like simple electrical conductors between the discharge and the silicon wafer. They act as if they would focus the current on smaller areas. The average diameter of impacts is about five times smaller if the silicon wafer is coated by a CNTcarpet. The underlying silicon surface is heated by the plasma and melts, forming a central spot surrounded by a serrated trailing edge. The current density being about one order of magnitude larger when a CNT carpet is present, the induced magnetic field stirs the molten silicon, creating serrations all around the impact. Hot nanoparticles of carbon coming from the plasma fall and roll randomly on the silicon surface where they create wavy micro-channels. Nanowires that are detached from the surface are covered by nanoparticles of platinum in the plasma and embedded within an amorphous carbon layer deposited on the nanotube. However, these effects can only be observed if the current density is high enough (>%10 A mm À2 depending on the material) like in micro-EDM but not in nano-EDM.

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Tailored aluminium oxide layers by bipolar current adjustment in the Plasma Electrolytic Oxidation (PEO) process

Cited by 186 publications

References 19 publications

High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

High-Frequency-Induced Cathodic Breakdown during Plasma Electrolytic Oxidation

Dielectric breakdown and healing of anodic oxide films on aluminium under single pulse anodizing

Interaction of Discharges in Heptane with Silicon Covered by a Carpet of Carbon Nanotubes

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