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Usinage par Pulse ElectroChemical Machining (PECM) de superalliages base nickel employés pour des pièces aéronautiques fortement sollicitées thermomécaniquement : compréhension des phénomènes physicochimiques et optimisation du procédé

Abstract : Pulse Electro Chemical Machining PECM is an unconventional machining process (with no cutting tools) of complex shapes requiring high precision. This technology is based on the anodic oxidation of the metal and is distinguished by pulsed current synchronized to an oscillation of the cathode with a rectilinear translational movement. The electrolyte is continuously renewed allowing the evacuation of sludge of the dissolved metal. The PECM involves low inter-electrode gap (from 0.01 to 0.2 mm) which ensures high dimensional accuracy. The aim of the thesis is to understand the physico-chemical phenomena related to the anodic dissolution of nickel-based superalloys (René 65 and Inconel 718) in the usual electrolyte NaNO3. Because of the complexity of the microstructure of the studied superalloys, the different phases were synthesized and studied separately. It appears that the insoluble dissolution products formed during anodization are mainly composed of Ni and Nb oxides (for Inconel 718) and Ti and W oxides (for René 65), but also γ '' (Ni3Nb), γ '(Ni3Ti) phases as well as carbides of W, of Nb of Cr. Consequently, the dissolved elements in solution are mainly made of the major elements of the austenitic matrix. In order to ensure a homogeneous dissolution of the different phases, alternative media have been developed, in particular by adding chelating agents. An experimental device for simulating PECM conditions in the laboratory allowed to establish the dissolution efficiency of the alloy as a function of different current densities in usual and alternative environments. Finally, the use of these alternative media was tested on the PECM machine. An experimental design methodology was used for the René 65 to compare the efficiency of the alternative electrolyte with the usual one with optimized operating parameters. These pilot scale tests have been extended to Inconel 718 alloy. It appears that the use of specific electrolyte makes it possible both to reduce the production of metal hydroxide sludge and to limit the formation of anodic surface layers.
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https://hal.univ-lorraine.fr/tel-02558391
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Submitted on : Wednesday, April 29, 2020 - 3:39:47 PM
Last modification on : Thursday, April 30, 2020 - 1:37:34 AM

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  • HAL Id : tel-02558391, version 1

Citation

Mariem Msakni Malouche. Usinage par Pulse ElectroChemical Machining (PECM) de superalliages base nickel employés pour des pièces aéronautiques fortement sollicitées thermomécaniquement : compréhension des phénomènes physicochimiques et optimisation du procédé. Chimie. Université de Lorraine, 2019. Français. ⟨NNT : 2019LORR0267⟩. ⟨tel-02558391⟩

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