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Study of the micro-discharges / metallic surfaces interactions for a better understanding of the growth mechanisms within the PEO process

Abstract : Plasma electrolytic oxidation (PEO) is an electrochemical surface processing technique that allows the growth of protective oxide films on lightweight metals (Al, Ti, Mg). Contrary to conventional anodising, PEO operates at high current density and voltage which results in the ignition of micro-discharges (MDs) over the processed surface The aim of this work was to investigate the characteristics of the MDs under different processing parameters and to correlate these characteristics with the microstructure of the produced oxide layers in order to better understand the oxide growth mechanisms. Firstly, PEO sequenced treatments were conducted by changing the electrical parameters in the course of a treatment. Results revealed a particular behaviour of the MDs which depends not only on the applied electrical parameters but also on the morphology of the growing layer. Results also evidenced an earlier transition to the beneficial “soft” sparking regime, contributing to a significant improvement of the microstructure of the oxide layer as well as process energy consumption. Time-resolved optical characterizations of the PEO process pointed out a correlation between ignition of MDs and the dynamic of the surrounding gas bubbles at the oxide / electrolyte interface. Particularly, results proved the existence of inner MDs during the “soft” sparking regime. Secondly, a multi-scale characterization of the typical “pancake” structure formed during the transition to the “soft” regime revealed the formation of a lamellar nanocomposite structure consisting of periodical alternations of alumina and metastable 1:1 mullite lamellae. Finally, two new opportunities for the PEO process were explored. The feasibility of duplex treatment involving cold-spray and PEO technologies was demonstrated and the possibility to produce metallic oxide (nano-) particles was proposed.
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https://hal.univ-lorraine.fr/tel-02961871
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Submitted on : Thursday, October 8, 2020 - 5:54:46 PM
Last modification on : Friday, October 9, 2020 - 3:32:31 AM

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  • HAL Id : tel-02961871, version 1

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Vitalios Ntomprougkidis. Study of the micro-discharges / metallic surfaces interactions for a better understanding of the growth mechanisms within the PEO process. Plasma Physics [physics.plasm-ph]. Université de Lorraine, 2020. English. ⟨NNT : 2020LORR0077⟩. ⟨tel-02961871⟩

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