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Toutes :: 2007, 2011
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2011

Articles:

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

2007

Articles:

Morniroli, J. P., Redjaïmia, A. and Nicolopoulos, S.
Ultramicroscopy, 107(6-7):514-522
2007
ISSN: 0304-3991

Resume: In a previous study, it was reported that the possible space groups of a crystal can be identified at a microscopic or nanoscopic scale, thanks to microdiffraction patterns obtained with a nearly parallel electron incident beam focused on a very small area of the specimen. A systematic method was proposed, which consists of the observation of a few microdiffraction patterns displaying at least two Laue zones. These microdiffraction patterns can also be obtained by using an electron precession equipment. In this case, the patterns display a very large number of reflections in the Laue zones whose intensity is the integrated intensity. These original features greatly facilitate the space group identification method and are particularly useful when the high-order Laue zones (HOLZ) are not visible on microdiffraction patterns or when very thin specimens are not available. (c) 2006 Elsevier B.V. All rights reserved.

Equipe: Département SI2M : Microstructures et Contraintes

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