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Understanding spheroidal graphite growth in cast irons is a long standing problem for which several mechanisms have been proposed. During the last decade, observations using transmission electron microscopy added new information about the stacking of graphite layers, leading eventually to propose other mechanisms than previously thought of such as repeated 2D-nucleation of new growth blocks and their lateral extension at the surface of the spheroids. Furthermore, it has been recently realized that elements known to strongly affect graphite shape are also those that are surface active. This is illustrated here in the case of antimony which is known to lead to spheroidal graphite degeneration when added at some tens of ppm. Using atomic resolution microscopy, segregation of antimony could be evidenced at the graphite/matrix interface of both spheroids and protuberances. This strongly suggests that accumulation of antimony repelled magnesium from the graphite surface until growth of spiky protuberances replaced spheroidal growth.

Microstructure control by solidification processing - Outcome from a European thematic network

The isothermal decomposition of austenite to ferrite and graphite in a spheroidal graphite cast iron was investigated by dilatometry, metallography and image analysis. The results gave quantitative, although indirect, information on the kinetics of carbon transfer from austenite to graphite, as well as on the kinetics of the austenite to ferrite and graphite transformation. The relations between these kinetics and the graphite nodule count was highlighted. The incubation period before ferrite growth was found to be associated with a global contraction of the material, in spite of the related increase of the graphite volume fraction. Calculations showed good agreement with experimental results, except for the rate of carbon transfer, which was found to be much slower experimentally than predicted by calculations based on the volume diffusion of carbon. Possible reasons for this discrepancy are discussed.

A model of the solidification of spheroidal graphite cast iron (SGI) has been detailed in Part I. It was designed to allow the description of the successive steps of solidification of hypereutectic as well as hypoeutectic alloys, i.e. the pro-eutectic deposits and the eutectic reaction. In the present paper, this model is used first as a tool to analyse the main features of the solidification of SGI as experimentally established. Calculations are then described which were carried out to simulate a series of test castings from which sufficient experimental information was obtained to discuss the validity and the limits of the present modelling and simulating approach. Particular emphasis is put on the nucleation and growth of graphite nodules and on the precipitation of non-eutectic austenite during the eutectic stage.

La maitrise de la formation des differentes microstructures pouvant apparaitre lors de la solidification et des transformations de phases des fontes necessite le developpement de modeles physiques appropries, que ce soit pour mieux comprendre les conditions de formation de ces structures ou pour l’optimisation des procedes de coulee. Dans ce travail, nous presentons les principales etapes de la formation de la microstructure des fontes ferrito-perlitiques a graphite spheroidal. Nous avons en particulier cherche a correler les connaissances deduites d’observations sur produits coules et les resultats d’etudes de laboratoire. L’accent est mis sur la germination des nodules de graphite, les caracteristiques de la reaction eutectique, le developpement des microsegregations en elements substitutionnels (Si, Mn,...) et la decomposition de l’austenite en ferrite et graphite ou en perlite.

Cet article propose une revue des applications de l’analyse automatique d’images dans le domaine de la metallurgie des superalliages a base de nickel. Apres une presentation rapide du developpement de ces materiaux insistant plus particulierement sur les differents types de microstructure rencontres, un bilan est fait de l’emploi de l’analyse d’images en tant qu’outil de controle et d’etude dans les principales entreprises francaises interessees par ces alliages. Il apparait que l’utilisation de cette technique est encore relativement limitee dans ce domaine, ceci resultant en grande partie de difficultes d’imagerie. Quelques approches originales extraites de la litterature sont cependant presentees, en faisant ressortir l’existence de differentes echelles pertinentes pour la caracterisation structurale de ces materiaux. Une derniere partie est consacree a l'evocation d’autres techniques en cours de developpement pouvant egalement presenter un interet en matiere de caracterisation quantitative de la microstructure des superalliages a base de nickel

We have measured the internal friction and the dynamic modulus of an Fe–38 at.% Al alloy using a forced torsion pendulum working between 10−3 and 10 Hz. The measurements have been carried out as a function of temperature (from room temperature to 1200 K) and as a function of frequency. Two peaks have been observed in the internal friction spectra, at about 780 and 1100 K, which are largely superposed in the intermediate temperature range. Both peaks and the corresponding modulus defect shift in temperature with the oscillation frequency, and can be attributed to relaxation mechanisms. Previous results in the literature seem to indicate that the low temperature peak is the Zener relaxation of Al atoms. The activation energy of the high-temperature peak, referred to as P1 peak because it has not been studied previously, has been determined to be Hact = 2.87 eV, from the results of measurements at different temperatures and frequencies. We discuss the possible mechanisms, which could be responsible of this P1 peak, and suggest that it could be attributed to the intrinsic movements of left angle bracket1 0 0right-pointing angle bracket perfect dislocations over the Peierls barrier by kink pair formation in the B2 ordered FeAl.

El presente trabajo se realizó sobre una aleación base Al-Si-Cu, muy utilizada en el sector automotriz para la fabricación de monoblocks y cabezas de motor. Se utilizó el análisis térmico diferencial (DTA) para determinar las temperaturas de inicio y fin de las reacciones que ocurren durante la solidificación de la aleación A319 a tres velocidades de enfriamiento (2, 10 y 20 ºC/min) con 12 y 136 ppm de Sr como agente modificador. Se detectaron tres reacciones eutécticas, la más interesante entre ellas es la formación de fases ricas en cobre, con temperaturas de formación que disminuyen al aumentar la velocidad de enfriamiento y el contenido de Sr. Finalmente, se efectuó un microanálisis empleando microscopio electrónico de barrido para determinar la distribución de los elementos en las fases obtenidas This work was carried out over a basic Al-Si-Cu alloy, widely used in the automotive industry for production of monoblocks and motor heads. Differential thermal analysis (DTA) was used to determine the reaction temperatures from beginning to end of the solidification process of alloy type A319 , using three cooling rates (2, 10, and 20 ºC/min) on samples with 12 and 136 ppm of Sr as modifying agent. Three eutectic reactions were found, one of these reactions corresponds to eutectic reaction of phases rich in copper and it was also found that the reaction temperature decreases when the cooling rate increases and also when the strontium content increases. Microanalysis using electron microscopy sacnning was performed, to determine the element distribution in the resulting phases

International audience; DTA analysis was used to investigate the solidification reactions of alloy A319 with either 12 or 136 ppm of Sr added. Strontium does not affect primary solidification of (Al) dendrites but modifies the kinetics of the (Al)–Si eutectic. The effects of Sr level and of cooling rate on the characteristic temperatures for the (Al)–Si and other eutectic reactions are described.

Experimental data related to the evolution of the distribution of solutes during directional solidification of an aluminium-rich Al-Cu-Mg-Si alloy with a columnar dendritic structure are described. Then results concerning the effect of solidification conditions on the overall solidification kinetics of this alloy are presented for both equiaxed dendritic and columnar dendritic structures. The predictions of a numerical model previously developed to simulate the solidification of multicomponent alloys at the dendritic scale are used to discuss the experimental results.

Purpose: The Achieve inner lumen mapping catheter can be used with the cryoballoon to assess real-time isolation of pulmonary vein (PV) during cryoablation and to act as a supporting guidewire during balloon positioning. We sought to analyze the feasibility of this novel catheter and to assess real-time PV isolation during cryoablation. Methods: Patients undergoing 28-mm cryoballoon PVI using the Achieve catheter were included from two centers. Each application lasted 5 min. Real-time PV recording during freezing and time to PV isolation were analyzed. Lastly, the number of applications needed to achieve PV isolation was investigated. Results: 68 pts (47 male; 61±10 yo) were included. Averaged procedure duration and fluoroscopy times were 118±24 min and 29±10 min. During the first application, PV potentials could be detected during freezing in 95.2%, 75.0%, 81.5% and 31.2% of the left superior (LSPV), left inferior (LIPV), right superior (RSPV) and right inferior (RIPV) PVs, respectively. When PV potentials were detected, they appeared in 5±2, 4±2, 4±2, and 3±2 dipoles in and the first cryoenergy application was successful in 68.7%, 82.8%, 80.0% and 90.6% of the LSPVs, LIPVs, RSPVs, and RIPVs, respectively. PV deconnection occurred at -38.4±8.8°C/54.5±34.8sec, -33.3±10.5/46.9±30.4sec, -34.4±12.1/44.4±30.5sec and –37.4±18.0/52.7±27.1sec for the the LSPVs, LIPVs, RSPVs, and RIPVs, respectively. At the end of the procedure, 100% of the PVs were isolated after 1.2±0.6 applications (from 1 to 4). ![Figure][1] Conclusion: Cryoablation in conjunction with the novel Achieve catheter is feasible, leading to high acute PV isolation rates. Real-time PV recording during freezing can be performed in most of the left PVs and the RSPVs while recording of RIPV potentials is harder due to stability issues. [1]: pending:yes

The evolution of intraslope basins during the Neogene-Pleistocene along the continental margins of the Gulf of Mexico, offshore Nigeria and Brunei is similar in that these basins have been essentially fed by river-deltaic sources and have been frequently affected by syn-sedimentary faulting and shale/salt diapirism.

Information obtained from the analysis of the spectra of the Townsend avalanche amplification provides the basis for the study of average microscopic behaviour of the electrons. The electrical field E is uniform, and the avalanches are triggered off at the cathode by a single primary electron. Experimental conditions are such that no secondary effects or space charge can take place. The results of these experiments (methane, 50

The establishment of the fundamental Sutton's formula is criticized; this formula is recovered by a more correct mathematical reasoning, and generalized. Applications are only evoked. Si critica l'impostazione della formula fondamentale di Sutton; si ricupera questa formula con un ragionamento matematico piu corretto e la si generalizza. Alle applicazioni si accenna solo. Критикуется вывод фундаменталъной формулы Суттона. Эта формула выводится заново с помощъю более корректных математических аргументов. Обсуждаются применеия.

We study some properties of weighted Sobolev spaces with asymptotic conditions appropriate to physical conditions on non compact space times. An existence and uniqueness theorem of non compact maximal space-like hypersurfaces for asymptotically flat metrics in a neighbourhood of the Minkowski's metric is proved.

Les donnees experimentales recentes montrent le role de la vitesse acquise dans la convection ascendante et la possibilite, a echelle suffisante, de preferer des termes d'entrainement ou de viscosite turbulente aux termes de diffusion. Dans un nuage convectif en voie de croissance, l'entretien de la vitesse acquise provient en partie des condensations sommitales, sans effets de convergence localisee. Les hypotheses de l'equilibre hydrostatique et de l'incompressibilite n'ont ici aucune valeur.

Every HTS is associated with an M 3 -loop, just as every affine space over 1 is associated with an elementary abelian 3-group. If E is an M 3 -loop, denote by ( E ) the corresponding HTS. Then |Aut (E) = | E | Aut E . When E is free among the M 3 -loops which are nilpotent of class 2, the groups Aut E and Aut ( E ) may be described. In particular, the automorphism group of the non-affine HTS of order 3 4 turns out to be a semi-direct product of GL(3, 3 ) by the exponent 3-group B 3 on 3 generators whose order is 3 7 .

Most seismic stratigraphic or seismic lithologic interpretations have been applied to clastic depositional systems. Because of their unique sedimentologic and mineralogic characteristics, carbonate rocks are more difficult to study using seismic data. Increased knowledge of carbonate deposits and their petrophysical parameters, and higher quality geophysical tools now permit a better understanding of carbonate rocks using seismic images. In this paper, seismic facies of carbonate rocks are characterized, step by step, from the basin to the supratidal environment. (1) Pelagic deposits (shales and micritic limestone layers) exhibit continuous, parallel reflections with an apparently high frequency. Chalk deposits display continuous high-amplitude reflections at the top and base with an internal reflection-free zone. (2) Talus deposits are characterized by discontinuous, oblique reflections of high amplitude. Carbonate debris flow generates chaotic reflections with hummocky surfaces. Channels exhibit erosional truncations. (3) Reef barriers are mound-shaped biogenic deposits that display marginal onlapping reflections. Overlying reflections drape the reefs, and underlying reflections exhibit pull-up or pull-down effects. Hyperbolic diffractions also may occur. (4) Platform border sands are mound-shaped oblique reflections of moderately high amplitude. (5) Inner shelf strata are characterized by parallel, continuous reflections typically displaying low frequency. Patch reefs may be distinguished within the inner shelf system (mound shape, drape of overlying reflections, velocity anomalies, and spurious events). (6) Where dolomitized, the intertidal to supratidal facies exhibit a "marbled" zone--a practically reflection-free zone with a few discontinuous reflections. Diagenetic events, such as paleokarst zones, may be delineated using special analyses involving amplitude offset variations. The study of carbonate depositional environments and petrophysical characteristics provides a more complete geologic insight, including relative changes in sea level, within a sedimentary basin. Such studies are fundamental in analyzing carbonate reservoirs and their paleogeographic settings.

CONCENTRATION of radon in the air above the Atlantic Ocean at the K (‘kilo’) point was measured during May 28–June 28, 1962, and now we are attempting to relate the values of natural radioactivity to meteorological conditions.