Papers by Author: Régine Molins

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Authors: Bernard Lesage, L. Maréchal, Anne Marie Huntz, Régine Molins
Authors: Mohamed Sennour, Loïc Marchetti, Stéphane Perrin, Régine Molins, Michèle Pijolat, Olivier Raquet
Abstract: The oxide film formed on nickel-based alloys in Pressurized Water Reactors (PWR) primary coolant conditions (325°C, aqueous media) has been investigated by Transmission Electron Microscopy (TEM). TEM observations revealed an oxide layer divided in two parts. The internal layer was mainly composed of a continuous spinel layer, identified as a mixed iron and nickel chromite (Ni(1-x)FexCr2O4). Moreover, nodules of Cr2O3 were present at the interface between this spinel and the alloy. The external layer is composed of large crystallites corresponding to a spinel structure rich in iron (Ni(1-z)Fe(2+z)O4) resulting from precipitation phenomena. The influence of alloy surface defects was also studied underlining two main consequences on the formation of the passive film e.g. the internal layer. On one hand, the growth kinetics of the internal spinel rich in chromium increased with the surface defect density. Besides that, when the defect density increased, the oxide scale became more finely crystallized. This result agrees with a growth mechanism due to a rate limiting process of diffusion through the grain boundaries of the oxide. On the other hand, the quantity of Cr2O3 nodules increased with the number of surface defects, revealing that the nodules nucleated preferentially at defect location.
Authors: G. Calvarin-Amiri, Régine Molins, Anne Marie Huntz
Authors: G. Calvarin-Amiri, Bernard Lesage, Anne Marie Huntz, Régine Molins
Authors: Marion Chieux, Régine Molins, Luc Rémy, Cecilie Duhamel, Mohamed Sennour, Yannik Cadoret
Abstract: The present work, performed on nickel aluminides deposited on a single Ni-based superalloy AM1, focuses on the effect of the following several parameters on the microstructural and chemical changes occurring during isothermal heat treatment at 1100°C for 50h : -oxygen pressure by comparing heat treatment under ambient air (PO2 = 0.2 bar) and under secondary vacuum (PO2 = 0.2x10-6 bar). -cooling rate after isothermal heat treatment by comparing furnace cooling (3°C/min) and water quenching (500°C/min). -Pt addition in the coating by comparing NiAl and NiPtAl coatings. Characterizations were performed using SEM, analytical TEM and electron microprobe analyses. The results show that these parameters have a strong influence on both the microstructural evolution and the oxidation of the thermal barrier coating (TBC) system. Appropriate heat treatments are essential to improve interfacial resistance and increase the durability of TBC systems.
Authors: Eric Andrieu, A. Germidis, Régine Molins
Authors: C. Salmon, D. Tiberghien, Régine Molins, Christian Colin, Francis Delannay
Authors: J. Balmain, C. Savall, Régine Molins, C. Séverac, C. Haut, Anne Marie Huntz
Authors: Sophie Barradas, Michel Jeandin, Régine Molins, F. Borit, L. Berthe, C. Bolis, M. Boustie, M. Arrigoni, M. Ducos
Abstract: Three interface factors may influence thermally-sprayed coatings adhesion: interface morphology (as usual), thermal and chemical features. It was shown that these three aspects of adhesion mechanisms are shown to be dependent and very local. It is especially true for cold spray which is one of the most promising spray processes. As this spraying technique is based on rapid deformation, cold spray coating/substrate interfaces show local morphological, thermal and chemical features, in a way that none of them can be neglected. LASAT is particularly suitable for testing these coatings because it can be applied to small areas (~1 mm²). From this, it has the outstanding advantage to be sensitive to fine-scaled phenomena responsible for coating adhesion.
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