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Le rôle des éléments d'alliage sur la passivation des alliages Ni-Cr-Mo

Abstract : In this dissertation, the role of alloying elements on the passivation behavior of synthetic Ni-Cr, Ni-Cr-Mo alloys, commercial Ni alloys, and a novel Ni-Cr-Fe-Ru-Mo-W HEA was investigated. Elemental currents were decomposed from the polarization curve, which gives elemental behavior during the active-passive transition domain, the passive domain, and the transpassive domain for these Ni-based alloys. Spontaneous passivation and anodic passivation of Ni alloys were studied. Mo plays a critical role in spontaneous passivation. It was found that Mo enriched as Mo(IV) on the surface during spontaneous passivation and oxidized to soluble Mo(VI) during anodic passivation. Commercial Ni alloy with low Mo content and high Cr content could not spontaneously passivate in the HCl solution. In neutral NaCl solution, Mo enriched during the transpassive domain and dissolved during repassivation. It was concluded that the presence of Mo in the passive film was closely associated with the history of the alloy and largely influenced by potential and pH. The novel Ni-Cr-Fe-Ru-Mo-W HEA exhibited excellent corrosion resistance in H2SO4 solution indicated by spontaneous passivation, the low passive current in the polarization curve, and the absence of detectable elemental dissolution during the active peak. Spontaneous passivation of the HEA was different from that for Ni-Cr-Mo alloys, which did not occur immediately after the surface oxide was cathodically removed.
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Xuejie Li. Le rôle des éléments d'alliage sur la passivation des alliages Ni-Cr-Mo. Chimie analytique. Université Paris sciences et lettres, 2020. Français. ⟨NNT : 2020UPSLC022⟩. ⟨tel-03553307⟩

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