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Publications: Articles

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Appolaire, Benoit, Perevoshchikova, Nataliya, Teixeira, Julien and Denis, Sabine
Solid State Phenomena, 172-174(Part 1):1214-1219
ISSN: 1012-0394

Resume: We have adapted the Quickhull algorithm with the general dimension Beneath-Beyond algorithm [6] for computing the convex hull of the Gibbs energy hypersurface of multicomponent two-phase alloys. We illustrate the salient features of our method with calculations of isothermal ferrite-austenite equilibria in Fe-C-Cr. Finally, successive equilibrium calculations in a Fe-C-Cr-Mo steel over a large temperature range show the benefit of computing the convex hull before performing the conventional Newton-Raphson search.

Equipe: Département SI2M : Microstructures et Contraintes

Pushkareva, Irina, Redjaimia, Abdelkrim, Moulin, Antoine and Valle, Nathalie
Solid State Phenomena, 172-174(Part 1):839-844
ISSN: 1012-0394

Resume: A detailed analysis of the evolution of industrial Dual Phase (DP) steel microstructures is carried out as a function of various annealing and tempering conditions. Advanced characterization techniques such as Parallel Electron Energy Loss Spectroscopy (PEELS) in the TEM and high spatial resolution Secondary Ion Mass Spectrometry (NanoSIMS) are employed in order to provide qualitative and quantitative measurements of local carbon concentration in the martensite. For certain annealing and tempering conditions, it is observed that local variations in carbon levels have occurred inside the individual martensite islands. These carbon variations strongly influence the damage behaviour of the steel. During tensile tests, a clear dependence of the damage mode on the local martensite carbon content is observed. Better knowledge of the relationship between the microstructure evolution at the sub-grain level and the damage behaviour can facilitate the design of DP steels with improved damage resistance.

Equipe: Département SI2M : Microstructures et Contraintes

Berveiller, S., Malard, B., Wright, J., Patoor, E. and Geandier, G.
Acta Materialia, 59(9):3636-3645
ISSN: 1359-6454

Resume: Two synchrotron diffraction techniques, three-dimensional X-ray diffraction and Laue microdiffraction, are applied to studying the deformation behaviour of individual grains embedded in a Cu(74)Al(23)Be(3) superelastic shape memory alloy. The average lattice rotation and the intragranular heterogeneity of orientations are measured during in situ tensile tests at room temperature for four grains of mean size similar to 1 mm. During mechanical loading, all four grains rotate and the mean rotation angle increases with austenite deformation. As the martensitic transformation occurs, the rotation becomes more pronounced, and the grain orientation splits into several sub-domains: the austenite orientation varies on both sides of the martensite variant. The mean disorientation is similar to 1 degrees. Upon unloading, the sub-domains collapse and reverse rotation is observed. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Equipe: Département SI2M : Microstructures et Contraintes

Hell, Jean-Christophe, Dehmas, Moukrane, Allain, Sebastien, Prado, Juscelino Mendes, Hazotte, Alain and Chateau, Jean-Philippe
ISIJ International, 51(10):1724-1732
ISSN: 0915-1559

Resume: We elaborated two carbide-free bainitic steels with different microstructures through specific alloy design and austempering process. Microstructural characterizations were performed by means of EBSD analysis and in-situ high energy synchrotron diffraction in order to evaluate the phase fractions and the carbon content in the retained austenite, as well as the microtextures. These microstructural features were correlated to the tensile properties. Both steels exhibited an excellent compromise between high strength (above 1 250 MPa), good ductility (uniform elongation up to 14%) and high fracture strain (reduction of area up to 46%). The volume fraction of MA blocks (blocks of retained austenite partially transformed into fresh martensite during the final cooling at room temperature) was a key relevant parameter that strongly influenced the work-hardening at the expense of the damaging processes at high strain.

Equipe: Département SI2M : Microstructures et Contraintes

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