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2012

Articles:

Dehmas, Moukrane, Salib, Matthieu, Geandier, Guillaume, Gautier, Elisabeth, Karnatak, Nikhil and Martin, Olivier
Matériaux et techniques, 100:103-105
2012

Equipe: Département SI2M : Microstructures et Contraintes

Geandier, G., Aeby-Gautier, E., Settefrati, A., Dehmas, M. and Appolaire, B.
Comptes Rendus Physique, 13(3):257-267
2012
ISSN: 1631-0705

Resume: High energy X-ray diffraction is a powerful tool, able to follow phase transformations during complex thermal or thermo-mechanical treatments. High energy allows one to study volumic specimens of a few mm(3) and get successive data within a few seconds or less. The technique is described with different experimental setups (heating devices, detectors for diverse acquisition times) allowing diverse ranges for heating and cooling rates. Three examples are considered to illustrate the results obtained by using high energy X-ray diffraction. The first one corresponds to a simple diffusive phase transformation during an isothermal thermal path for the alpha-beta transformation in a titanium alloy, highlighting the diffusive character considering the cell parameter evolutions of the parent phase. The second one illustrates the precipitation sequences observed during ageing of a beta-metastable phase in a titanium alloy that was not obtained by TEM. The last example illustrates the phase evolutions during ageing of a martensitic steel showing the complexity of cell parameters evolution and some evolutions of the stress state. (C) 2011 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

Equipe: Département SI2M : Microstructures et Contraintes

Borgese, L., Gelfi, M., Bontempi, E., Goudeau, P., Geandier, G., Thiaudière, D. and Depero, L. E.
Surface and Coatings Technology, 206(8-9):2459-2463
2012
ISSN: 0257-8972

Resume: Atomic Layer Deposition (ALD) allows the deposition of thin films onto flat as well as complex geometry surfaces with excellent conformality. Thicknesses of few atomic layers can be achieved. Moreover, low-temperature deposition is possible and this enables the change of surface properties of many kinds of materials. Good adhesion characteristics and also good mechanical performance of ALD deposited thin films make the technique extremely interesting for several applications, as for example micro-electronics. TiO2 is a well studied semiconductor material because of its multifunctional properties that open a wide range of applications for example in photocatalysis, optics and solar cells. ALD is extremely completive to other technique, to deposit titania thin films, employed even to improve the biocompatibility of many kind of materials. TiO2 thin films are deposited with ALD technique at low temperature (90 degrees C) onto Kapton substrate and then crystallized ex-situ after annealing at 300 degrees C. X-ray diffraction (XRD) techniques are very suitable for the analysis of structure and microstructure of films and surface layers. In this work, XRD in combination with in situ tensile testing has been applied for the first time to measure elastic properties (elastic modulus and Poisson ratio) of TiO2 anatase thin films obtained by ALD. For the experimental conditions, the tensile stage was installed in a Synchrotron laboratory of Soleil. The information extracted from diffraction patterns is presented. (C) 2011 Elsevier B.V. All rights reserved.

Equipe: Département SI2M : Microstructures et Contraintes

2011

Articles:

Appolaire, Benoit, Perevoshchikova, Nataliya, Teixeira, Julien and Denis, Sabine
Solid State Phenomena, 172-174(Part 1):1214-1219
2011
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
2011
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

Dehmas, M., Kovac, J., Aeby-Gautier, E., Appolaire, B., Denand, B. and Da-Costa-Teixeira, J.
Solid State Phenomena, 172-174:396-401
2011

Equipe: Département SI2M : Microstructures et Contraintes

Koutsoukis, T., Redjaïmia, A. and Fourlaris, G.
Solid State Phenomena, 172-174(Part 1):493-498
2011
ISSN: 1012-0394

Resume: Superaustenitic stainless steels exhibit excellent corrosion resistance, at a wide variety of exposure temperatures, especially in chloride containing environments, coupled with desirable mechanical properties. Previous studies have shown that these steels are prone to precipitation of secondary phases, such as sigma phase (sigma), chi phase (chi). Laves-phase, carbides, nitrides or secondary austenite, when exposed at elevated temperatures, directly affecting their mechanical properties and corrosion behaviour. A detailed study of the effect of isothermal ageing on the microstructure of S32654 (Fe-24Cr-21Ni-7Mo-0.5N-0.013C) and S31254 (Fe-20Cr-18Ni-6Mo-0.2N-0.012C) superaustenitic stainless steels was carried out. Samples were aged within the temperature range of 650 degrees C to 950 degrees C for times up to 3000 h. Following ageing, precipitation of secondary phases was clearly observed with precipitates varying in volume fraction, size, shape and spatial distribution. Several secondary phases were identified via transmission electron microscopy (TEM) and electron diffraction (ED). The orientation relationships between the austenitic matrix and the secondary phases were identified. Interaction and also phase transformation among different types of precipitates, such as between precipitates and the austenitic matrix were observed and an attempt of understanding these phase transformations was carried out.

Equipe: Département SI2M : Microstructures et Contraintes

Daoudi, M., Triki, A. and Redjaïmia, A.
Journal of Thermal Analysis and Calorimetry, 104 (2):627-633
2011

Equipe: Département SI2M : Microstructures et Contraintes

Berveiller, S., Malard, B., Wright, J., Patoor, E. and Geandier, G.
Acta Materialia, 59(9):3636-3645
2011
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
2011
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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