The red giants in NGC 6633 as seen with CoRoT, HARPS and SOPHIE

The open cluster NGC 6633 was observed with CoRoT in 2011 and simultaneous high-resolution spectroscopy was obtained with the SOPHIE and HARPS spectrographs. One of the four targets was not found to be a cluster member. For all stars we provide estimates of the seismic and spectroscopic parameters.Comment: Proc. of the workshop "Asteroseismology of stellar populations in the Milky Way" (Sesto, 22-26 July 2013), Astrophysics and Space Science Proceedings, (eds. A. Miglio, L. Girardi, P. Eggenberger, J. Montalban

Etude des mécanismes de recristallisation de nouveaux alliages à base de Ni

Les travaux portent sur deux nuances d alliages Ni-Cr-W, l une contenant des précipités de W (EM722) et l autre non (EM721). Les matériaux forgés, fournis par Aubert & Duval, présentaient des microstructures hétérogènes avec de très gros grains. Dans un premier temps, une procédure thermomécanique a été développée afin d obtenir un état de référence avec une microstructure homogène avec une faible taille de grains et une texture relativement peu accusée. A partir de cet état de référence, l évolution de la texture, au cours du laminage à froid (différents taux de réduction), a été analysée par diffraction des neutrons et a montré un renforcement de la texture de type Laiton. Les mécanismes de déformation ont été étudiés en microscopie électronique en transmission et par EBSD (Electron BackScatter Diffraction) afin de comprendre la formation de ce type de texture. Les bandes de cisaillement sont supposées être un facteur important pour la formation de ce type de texture. A partir des états déformés, la cinétique de recristallisation a été déterminée pour deux températures (700C et 900C) à partir de mesures de microdureté et par EBSD. Les mécanismes de recristallisation ont été étudiés par MET. Le mécanisme de SIBM (Strain Induced grain Boundary Migration) est le mécanisme prépondérant pour la nuance EM721. Pour l autre nuance, EM722, possédant des précipités de W, le mécanisme de SIBM est présent, mais en plus, un second mécanisme de PSN (Particle Stimulated Nucleation) a été mis en évidence. De plus, quel que soit le mécanisme de recristallisation, une fois que les germes sont formés, ils maclent très rapidement. Par conséquent, une étude complémentaire sur l évolution des joints de macle pendant la recristallisation primaire a été réalisée, en employant l EBSD et surtout le système ASTAR installé dans un MET. Il a alors été montré que cette évolution dépend à la fois de la taille des grains et de l énergie stockée par les grains pendant la déformation. Enfin, une simulation de la recristallisation primaire de type Monte-Carlo a également été mise en œuvre. Son originalité réside notamment dans sa capacité à rendre compte de la formation des joints de macles cohérents et rectilignes.This work focuses on two grades of Ni-Cr-W alloys, one containing W precipitates (EM722) and the other not (EM721). The forged materials, provided by Aubert & Duval, had heterogeneous microstructures with very large grains. At first, a thermo-mechanical procedure was developed to obtain a reference state with a homogeneous microstructure with a small grain size and a texture relatively weak. From this reference state, the texture evolution during cold rolling (different reduction rates), was analyzed from neutron diffraction measurements and showed the strengthening of the Brass-type texture. The deformation mechanisms were studied by TEM (transmission electron microscopy) and EBSD (Electron Backscatter Diffraction) to understand the formation of this type of texture. The formation of shear bands is assumed to be the most important factor for the formation of such a texture. From the deformed states, the recrystallization kinetics was determined for two temperatures (700C and 900C) from micro-hardness and EBSD measurements. The recrystallization mechanisms were investigated by TEM. The SIBM (Strain Induced Grain Boundary Migration) mechanism is the predominant mechanism for the EM721 material. For the other one (EM722), which has W precipitates, the SIBM mechanism is present, but a second one (PSN: Particle Stimulated Nucleation) has also been evidenced. Furthermore, regardless of the mechanism of recrystallization, once the nuclei are formed, they twin quickly. Therefore, a further study on the evolution of twin boundaries during primary recrystallization was performed, using EBSD and especially the ASTAR system installed in a TEM. It has been shown that the twin development depends both on the grain size and the stored energy during the deformation. Finally, a Monte Carlo simulation of the primary recrystallization was also implemented. Its originality lies especially on its ability to create coherent and straight twin boundaries.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

POLYCRYSTALLINE MODELLING OF UDIMET 720 FORGING

International audienceA crystalline modelling of deformation implemented in a finite element code coupled to a recrystallization Cellular Automaton code is proposed and applied to forging processes of superalloys. The coupled modelling is used in order to obtain a better understanding of the microstructural evolution of superalloys during high temperature forging at different strain rates and temperatures. The framework of the modelling is large plastic deformation and large lattice rotation. The used internal variables are dislocations densities on slip systems of the different phases. Modelling is based on viscoplatic constitutive and hardening laws at the scale of the slip systems and describes local strain and stress fields as well as the stored energy and the rotation of the lattice in the grains of the microstructure. At different steps of deformation, formation of subgrains, annihilation of dislocations, nucleation, growth and new orientation of grains are computed. The 3D aggregates representing the superalloy, are built up from Electron Back Scattered Diffraction method (EBSD) by means of a high resolution Scanning Electron Microscope. The phases are identified by means of EBSD, chemical analysis (EDS) and observations with a Scanning Electron Microscope. In this paper the studied aggregate is realised from a semi product of Udimet 720. Such technique is able to give us, a realistic description of the crystalline orientation, morphology and position of grains in the aggregate. The Finite Element meshing is deduced from the EBSD analysis. At high temperature, the Udimet 720 is constituted by a γ matrix with a Face Centred Cubic structure (FCC) and γ' precipitates (Ni3(Ti,Al)) with a Simple Cubic structure (SC). The various material parameters used for the coupled modelling are previously determined from compression tests performed at several strain rate and temperature; The dislocation densities are measured from Transmission Electronic Microscope

Recrystallization and grain growth at the interface of a bimetallic colaminated strip composed of two different Fe-Ni alloys

International audienceRoll bonding is a solid-state welding process widely used to manufacture layered metal composites. Particular properties may thus be obtained using the physical features of each material of the composite. Bimetal plates consisting of two different Fe-Ni alloys were made by roll bonding followed by heat treatment for 90 minutes at various annealing temperatures. The effects of post-rolling heat treatments on the bonding strength of a bimetal strip were investigated in relation to the interface microstructure evolution. Both recrystallization and grain growth took place at the interface during annealing. In particular, nucleation of new grains as well as growing grains crossing the interface may have contributed to the improvement of the bonding strength. Moreover, diffusion through the interface was found to drastically enhance the bonding strength from 850°C up to 1050°C. However, excessive grain growth associated to porosity occurrence probably caused the saturation of the bonding strength beyond 1050°C

On the recrystallization and texture of Fe-36%Ni alloy after accumulative roll bonding and annealing at 600 °C

Microstructure and texture evolution of Fe-36%Ni (wt.%) alloy after 1, 5 and 10 accumulative roll-bonding (ARB) cycles and annealing at 600 °C up to 3600 seconds were studied using electron backscatter diffraction. Microstructural and textural changes after ARB and annealing were compared to those existing in the literature after conventional rolling. The microstructure was not stable at 600 °C for all ARB samples even after 3600 seconds of annealing. The recrystallization texture was dominated by the Cube {001} texture component. Recrystallization kinetics were determined using microhardness measurement and were close to those after cold rolling with Avrami time exponent around unity. The texture evolution at high strain was discussed in terms of grain boundary migration obstruction by the formation of layer interfaces and small recrystallized grains near the bonded interfaces

Optimization of microstructural evolution during laser cladding of Ni based powder on GCI glass molds

International audienceIn the glass industry, laser cladding is an innovative surfacing technique of depositing a layer of nickel to protect glass mold against corrosion, abrasion and thermal fatigue. This method (powder fusion by projection), well known in additive manufacturing represents a real technological leap for the glass industry. However, during laser cladding of Ni-based powder on gray cast iron, cracks can be observed for some process conditions. These cracks are often due to the Heat Affected Zone which creates structural stresses linked to the development of a martensitic structure in the ferritic matrix of the lamellar graphite cast iron. The aim of this work is to observe the impact of laser cladding (without substrate pre-heating usually used to limit cracking) on coating behavior but also on flake-graphite cast iron substrates. The microstructure and the mechanical properties were studied around the interface cladding/substrate. The impact of the processing parameters (power P, scanning speed v and powder feeding rate PFR was studied by using the ANOVA (ANalysis Of VAriance) technique. It has been observed that laser cladding on graphite cast iron without cracking is possible by limiting the linear energy induced by the process. Optimization of the processing parameters in order to obtain the industrial expected geometry of the coating has also been proposed

Study of the microstructure and texture heterogeneities of Fe–48wt%Ni alloy severely deformed by equal channel angular pressing

International audienceA Fe-48wt%Ni alloy was processed by severe plastic deformation using equal channel angular pressing process. A stacking of 9 sheets was introduced and pressed up to two passes into die with an inner angles of Φ=90º and outer arc of curvature ψ= 17° at room temperature following route A. The same material in bulk form was also ECAPed up to one pass. The microstructure and the texture were investigated by means of electron backscattered diffraction and X-ray diffraction, respectively. To evaluate the mechanical response, Vickers microhardness was carried out. The given analyses concern the as-received sample, the peripheral and the central plates of the pressed stacks and the upper, the middle and the lower parts of the pressed bulk material. The deformation was heterogeneous and variations in texture and microstructure, resulting from different efficiencies in the shearing process, were locally noted. For the stacks samples, the microstructure evolved from equiaxed grains of 9 μm with high fraction of high-angle grain boundaries (around 90%) to a heterogeneous fine grain structure with an average grain size of 3 m after two passes. On the contrary, for the bulk sample, the evolution wa

Influence des conditions de refroidissement sur le comportement magnétostrictif des matériaux ferromagnétiques - approche par modèle biphasé

Un fort accroissement des matériels électriques est envisagé dans le domaine des transports, notamment aéronautiques. L'électrification de la chaîne de puissance nécessite, à spécifications égales, une masse et un volume plus importants des équipements par rapport aux précédentes solutions. Le bruit émis par ces systèmes (en particulier les transformateurs de puissance) n'est alors plus admissible. Des solutions matériau innovantes sont donc recherchées, allant de paire avec le développement de modèles prédictifs de ce bruit. Dans un transformateur le bruit acoustique est provoqué par des déformations périodiques de l'ensemble des tôles. Cette déformation a deux origines : i) les forces d'origine magnétique, associées aux gradients d'aimantation (effet structure communément appelé « effet de forme ») ; ii) la déformation de magnétostriction, déformation libre dépendant de l'état magnétique local du matériau. De par les géométries et les assemblages réalisés, seul ce deuxième type de déformation peut avoir une contribution significative au bruit perçu [1]. Des solutions à magnétostriction réduite sont alors recherchées par les métallurgistes nécessitant pour cela de tester différentes configurations matériau.   Le modèle multi échelle magnéto-mécanique développé au LMT depuis plus d'une dizaine d'années a montré de très bonnes capacités à pouvoir restituer le comportement magnétostrictif de nombreux matériaux [1-5]. Il peut à l'inverse permettre de définir des configurations idéales aboutissant à des comportements désirés tels qu'une magnétostriction de faible amplitude sur une gamme d'induction étendue. Parmi ces configurations, la structure bi-domaines qu'on retrouve par exemple dans les fer-silicium à grains orientés [4] semble la plus appropriée. Le comportement obtenu est cependant beaucoup trop anisotrope pour rendre cette solution viable. En revanche, on montre qu'une structure bi-domaines au sein d'un polycristal isotrope peut conduire à des déformations faibles relativement isotropes dans le plan de la tôle mais sur une gamme d'induction plus réduite. Les constantes du matériau doivent cependant respecter certaines conditions. Ce comportement théorique est effectivement observé expérimentalement pour un alliage fer-cobalt. On montre dans ce travail que la déformation de magnétostriction observée est fortement corrélée avec la structure en domaines (observations par effet Kerr). Cette structure est en particulier sensible aux contraintes résiduelles développées lors des traitements thermiques

Microstructure, Texture, and Mechanical Properties of Ni-W Alloy After Accumulative Roll Bonding

International audienceIn this study, the microstructure, texture, and mechanical properties evolution of Ni-14W (wt. %) alloy processed up to four cycles of accumulative roll-bonding (ARB) were investigated using electron backscatter diffraction, microhardness measurements, and tensile tests. The initial equiaxed grains, with an average size of 10 μm, underwent a strong refinement after ARB processing. The elongated ultrafine grains were parallel to the rolling direction, with a grain thickness of 0.2 µm. The texture after ARB processing was characterized by the typical rolling components (Copper, S and Brass), which showed a tendency toward stabilization after four cycles. The microhardness increased substantially (+86%) and seemed to saturate after three cycles. The tensile tests demonstrated that Ni-14W samples subjected to ARB processing exhibited high strength (> 1200 MPa after three ARB cycles) and very poor ductility

Microstructural Evolutions and Mechanical Properties of Drawn Medium Carbon Steel Wire

International audienceThis study focuses on the evolution in the microstructure, texture and mechanical properties of medium carbon steel wires obtained by wire drawing at Tréfissoud Company for the manufacturing of the spring mattress. Wire drawing induces elongation of grains in the direction of drawing with the development of the fibre texture parallel to the wire axis. Kinking and bending of cementite lamellae were observed during the drawing process. The work was carried out respectively on three states, wire rod and drawn states for two different amounts (ε %=43,6 and 60 %), using the optical and SEM microscopy, electron backscatter diffraction and X-ray diffraction analysis for examination of the microstructure and texture evolution, the hardness Vickers and tensile test to follow the curing of the studied wires