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Settefrati, A., Aeby-Gautier, E., Dehmas, M., Geandier, G., Appolaire, B., Audion, S. and Delfosse, J.
Solid State Phenomena, 172-174(Part 1):760-765
ISSN: 1012-0394

Resume: In the present study we focus on the precipitation processes during heating and ageing of beta-metastable phase in the near beta Ti-5553 alloy. Transformation processes have been studied using continuous high energy X-Ray Diffraction (XRD) and electrical resistivity for two different states of the beta-metastable phase. Microstructures have been observed by electron microscopy. Different transformation sequences are highlighted depending on both heating rate and chemical composition of the beta-metastable phase. At low temperatures and low heating rates, the hexagonal omega(iso) phase is first formed as generally mentioned in the literature. Increasing the temperature, XRD evidences the formation of an orthorhombic phase (alpha"), which evolves toward the hexagonal pseudo compact alpha phase. For higher heating rates or for richer composition in beta-stabilizing elements of the beta-metastable phase, omega phase may not form and alpha" forms directly and again transforms into alpha phase. A direct transformation from beta-metastable to alpha phase is observed for the highest heating rate. The formation of the metastable omega(iso) and alpha" phases clearly influences the final morphology of alpha.

Equipe: Département SI2M : Microstructures et Contraintes

Dehmas, Moukrane, Lacaze, Jacques, Niang, Aliou and Viguier, Bernard
Advances in Materials Science and Engineering, 2011:9
ISSN: 1687-6822

Resume: Inconel 718 is widely used because of its ability to retain strength at up to 650 degrees C for long periods of time through coherent metastable gamma `' Ni(3)Nb precipitation associated with a smaller volume fraction of gamma' Ni(3)Al precipitates. At very long ageing times at service temperature, gamma `' decomposes to the stable Ni(3)Nb delta phase. This latter phase is also present above the gamma `' solvus and is used for grain control during forging of alloy 718. While most works available on delta precipitation have been performed at temperatures below the gamma `' solvus, it appeared of interest to also investigate the case where delta phase precipitates directly fromthe fccmatrix free of gamma `' precipitates. This was studied by X-ray diffraction and transmission electron microscopy (TEM). TEM observations confirmed the presence of rotation-ordered domains in delta plates, and some unexpected contrast could be explained by double diffraction due to overlapping phases.

Equipe: Département SI2M : Microstructures et Contraintes

Faurie, D., Renault, P. -O., Geandier, G. and Le Bourhis, E.
Thin Solid Films, 520(5):1603-1607
ISSN: 0040-6090

Resume: Synchrotron x-ray radiation was used for in situ strain measurements in gold films on polyimide substrate during uniaxial deformation tests. We have used an area detector that allows inspecting multiple directions in the polycrystalline thin film without serial sectioning during straining. We show in this paper the configuration used and the attainable orientations on a pole figure for which the x-ray strains are measured. Moreover, we show the effect on the x-ray strains of the onset on plasticity, which was not detected by optical (macroscopic) strain measurement. (C) 2011 Elsevier B.V. All rights reserved.

Equipe: Département SI2M : Microstructures et Contraintes

Mourot, Mickael, Courleux, Alice, Dehmas, Moukrane, Gautier, Elisabeth, Geandier, Guillaume, Dezellus, Olivier, Claude Viala, Jean, Martin, Olivier, Karnatak, Nikhil and Danoix, Frederic
Solid State Phenomena, 172-174:747-752

Equipe: Département SI2M : Microstructures et Contraintes

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