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Determination and understanding of the role of alloying elements on the passive behavior of Ni-based alloys by electrochemical investigation

Abstract : Ni-based alloys are widely used in various engineering applications, such as oil and gas, nuclear power plant and chemical process, due to their excellent corrosion resistance and good mechanical properties at elevated temperature. To extend the sustainability and the versatility of Ni-based alloys, development of new grades or improvement of the existing ones is still ongoing. To carry out the alloy design, the study on the role of alloying elements on nickel-based alloys properties and corrosion resistance remains the best scientific approach. Within this framework, the main objective of this thesis is to develop a methodology based on electrochemical characterization and analysis for understanding the role of the alloying elements on the corrosion behavior and on the passive film properties of Ni-based alloys. The proposed methodology relies on successive electrochemical impedance spectroscopy measurements and advanced analyses of the impedance data, to follow the evolution of the passive film properties grown on different binary (Ni-Cr) and ternary (Ni-Cr-Fe) alloys at different potentials. The obtained impedance diagrams were interpreted with enhanced graphical method and fitted with Power-Law Model for giving physical meanings to passive film. This experimental procedure provides supplementary data from conventional polarization curves, such as evolution of the passive film thickness and resistivity profiles through the film. In this work, the role of alloying elements, especially chromium and iron, on the passive film properties and reactivity is studied. Understanding how alloying elements act on the passive film nature, structure and properties will provide some guidelines to engineers and scientists for designing or choosing the more adapted alloys. Finally, the proposed experimental method is also applied on certain commercial alloys. Their responses are compared with that of the closest binary and ternary alloys to evidence the discriminating factors that control the passive behavior.
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Submitted on : Friday, October 22, 2021 - 11:45:38 AM
Last modification on : Saturday, October 23, 2021 - 4:09:55 AM

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Zhiheng Zhang. Determination and understanding of the role of alloying elements on the passive behavior of Ni-based alloys by electrochemical investigation. Materials. Université de Lyon, 2021. English. ⟨NNT : 2021LYSEI050⟩. ⟨tel-03394931⟩

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