Littérature scientifique sur le sujet « Refusion à l'arc sous vide (VAR) »
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Articles de revues sur le sujet "Refusion à l'arc sous vide (VAR)"
JARDY, Alain, Isabelle CRASSOUS, Sylvain CHARMOND, Vincent DESCOTES, Stéphane HANS et Yvon MILLET. « Procédé de refusion à l’arc sous vide (VAR) ». Élaboration et recyclage des métaux, janvier 2022. http://dx.doi.org/10.51257/a-v1-m7822.
Texte intégralThèses sur le sujet "Refusion à l'arc sous vide (VAR)"
Chapelle, Pierre. « Étude expérimentale et modélisation de l'arc électrique dans le procédé de refusion var ». Vandoeuvre-les-Nancy, INPL, 2001. http://www.theses.fr/2001INPL004N.
Texte intégralEl, Mir Hafid. « Comportement de l'arc électrique et fusion de l'électrode consommable dans un four de refusion VAR ». Vandoeuvre-les-Nancy, INPL, 2005. http://www.theses.fr/2005INPL040N.
Texte intégralThe present study is aimed to improve our knowledge of the electric arc in the Vacuum Arc Remelting VAR process, as weil as characterize the cathode melting stage. The first step consisted in investigating, thanks to an experimental modulus, the behaviour of the electric arc during the remelting of zirconium alloys, for various operating conditions. High speed video camera observations have put in evidence the influence of the cathode tip shape and the effect of applying an external magnetic field on the movement of the clusters of cathode spots. Besides, infrared thermography measurements show qualitatively that the electrode height thermally affected by the arc is very sm ail and depends on the melt rate. The goal of the second part of this work is the development of a numerical model to simulate the motion of clusters of spots at the tip of the cathode. Coupling this approach with the simulation of the behaviour of a plasma jet emitted by a single cluster, previously established in LSG2M, enables calculating the power distribution at the VAR ingot top as a function of process parameters (current, electrode geometry and external magnetic field). Ln a third step, a thermal model of the consumable electrode during melting has been written, assuming a 2D axisymmetrical geometry. Using the operating parameters as model inputs, it predicts in particular the melting rate value and evolution of the cathode tip shape. The model was validated through simulating the three successive remeltings of a zirconium alloy, following an industrial processing route
Descotes, Vincent. « Précipitation des inclusions de nitrure de titane (TiN) dans un acier maraging au cours de sa refusion à l'arc électrique sous vide (VAR) ». Thesis, Université de Lorraine, 2014. http://www.theses.fr/2014LORR0262/document.
Texte intégralThe titanium contained in maraging steels combines itself with residual Nitrogen to form Titanium nitride precipitates (TiN), which are detrimental to fatigue properties. Understanding their formation may give some ways to reduce their sizes. A Sieverts apparatus was used to study denitriding reactions and precipitation reactions from a thermodynamic and kinetic point of view. According to these experiments, to thermodynamical data from literature, and to the Nitrogen content in the steel, the TiN inclusions are supposed to form during the solidification of the steel thanks to interdendritic segregation. A certain number of the TiN inclusions are found under SEM observations to be located next to another oxide or sulfur particle. A TEM observation reveals the existence of an orientation relationship between a nitride, a sulfur CaS and a spinel MgAl2O4. It suggests an epitaxial growth of the TiN on these two germs. This study was completed with ab initio calculations of surface energies and adsorption energies. This work supports the hypothesis of a heterogeneous nucleation of the Titanium nitrides on preexisting, stable particles in the liquid steel. A numerical model of the precipitation coupled to the interdendritic segregation of solutes is developed and introduced in the SOLAR software modelling the VAR ingot solidification. It evaluates the determinant influence of the initial Nitrogen mass fraction, germ number density and local solidification time on the TiN sizes
Banos, Julien. « Modélisation du procédé de refusion à l’arc sous vide : Échanges thermiques et défauts de solidification ». Electronic Thesis or Diss., Université de Lorraine, 2023. http://www.theses.fr/2023LORR0117.
Texte intégralThe Vacuum Arc Remelting (VAR) process is used in the production of high-added value metals such as titanium alloys or nickel-based superalloys for the aerospace industry. The control of solidification conditions is an important industrial issue in order to process ingots of adequate chemical homogeneity and free of solidification defects. The work presented in this manuscript aims at improving the description of heat exchanges in a VAR process model (SOLAR) and at proposing a new approach for the prediction of segregated channels type solidification defects. First, the description of the heat exchanges in the model between the electrode, the ingot, the mould and the cooling circuit has been improved. These modifications were validated by comparing the numerical results with measurements from real industrial melts. An original experimental apparatus for measuring the external mould temperature adapted to industrial melts was designed. This apparatus was used during an experimental campaign on an industrial site during the remelting of a titanium alloy. The measurements obtained were compared with the numerical results from SOLAR. These two activities led to a first implementation of the side-arcing phenomenon in the model. In parallel, a multi-scale numerical approach was developed to predict the formation of segregated channels as a function of local solidification conditions. A first study on a Sn-Pb alloy was carried out and a mathematical criterion was calculated from the results. This first study shows a much lower impact of the thermal gradient on the formation of segregated channels than that generally considered in the literature
Revil-Baudard, Mathieu. « Modélisation et étude de la macroségrégation au cours de la refusion à l'arc sous vide : application aux alliages de zirconium ». Thesis, Université de Lorraine, 2012. http://www.theses.fr/2012LORR0297/document.
Texte intégralVacuum Arc Remelting (VAR) is used to produce high performance alloys for the aeronautic (special steels, superalloys, titanium alloys) and nuclear (zirconium alloys) industries. As for all casting processes, the control of the chemical homogeneity and the metallurgical structure in VAR ingots is an important industrial issue. The goal of this thesis is to identify, for zirconium alloys in particular, the effects of the natural convection and the forced convection due to the electromagnetic stirring on macrosegregation. To this purpose, a numerical model has been developed. It is based on the solution of the coupled transient energy, momentum and solute transport equations, under laminar or turbulent flow conditions. The solidification modeling accounts for a full coupling between energy and solute transport in the mushy zone. The finite diffusion of solutes in both solid and liquid phases can be taken into account to describe microsegregation. In addition, chemically homogeneous Zircaloy-4 and M5® electrodes have been specially remelted in an industrial VAR furnace at the CEZUS plant in Ugine (Savoie, France). The macrosegregation of the ingots has been measured. The comparison between the experimental measurements and the simulation results showed that for an alloy with a large solidification interval (like Zircaloy-4), the solutal convection in the mushy zone could have an essential influence on the macrosegregation in the inner part of the ingot. Furthermore, the motion of equiaxed grains caused by a strong stirring seems to seriously intensify macrosegregation in the outer part of the ingot. For an alloy with a small solidification interval (like M5®), we have shown that the macrosegregation depends more specifically on the forced convection due to the type of stirring applied during the remelting
Hans, Stéphane. « Modélisation des transferts couplés de chaleur, de soluté et de quantité de mouvement lors de la refusion à l'arc sous vide (VAR) : application aux alliages de titane ». Vandoeuvre-les-Nancy, INPL, 1995. http://www.theses.fr/1995INPL023N.
Texte intégralSoller, Aude Jardy Alain. « Refusion à l'arc sous vide du superalliage 718 modélisation du procédé et étude de la formation des "white spots / ». Vandoeuvre-les-Nancy : INPL, 2006. http://www.scd.inpl-nancy.fr/theses/2006_SOLLER_A.pdf.
Texte intégralSoller, Aude. « Refusion à l'arc sous vide du superalliage 718 : modélisation du procédé et étude de la formation des "white spots" ». Vandoeuvre-les-Nancy, INPL, 2006. http://docnum.univ-lorraine.fr/public/INPL/2006_SOLLER_A.pdf.
Texte intégralSome very detrimental defects, called white spots, can form during the remelting of Alloy 718. Depleted in alloying elements, they are supposed to be generated by the fall of solid metallic precursors in the liquid pool. In a first step, a model aimed to simulate the remelting process, based on the SOLAR software, has been adapted to the remelting of Alloy 718, then validated by comparison between the simulation results and experimental observations of a remelted ingot. The characterization of electrodes and ingots has shown that large dendrites in the electrode could be the origin of dendritic white spots. This study also determines quantitatively the main characteristics of the three possible sources of discrete white spot precursors (electrode torus, shelf and crown) in terms of structure, composition and size. “Dipping” experiments of synthetic discrete white spots precursors allow a direct measurement of their melting kinetics. These results qualitatively validate a numerical model which describes the melting/solidification process of a spherical particle immerged in a liquid metal bath. Last, the behaviour of a discrete white spot in the liquid pool of a VAR ingot is determined through coupling the phase change model to a calculation of the precursor trajectory. The hydrodynamic and thermal behaviour of the liquid pool is calculated by SOLAR and the characteristics of each of the potential precursor origins are taken into account as input data. The overall model computes, for each origin, a precursor critical size leading to the formation of a white spot
Poullain, Thomas. « Etude numérique et expérimentale de l’évaporation sous vide d’alliages métalliques : application à la refusion VAR de Zircaloy-4 ». Electronic Thesis or Diss., Université de Lorraine, 2022. http://www.theses.fr/2022LORR0189.
Texte intégralComposition and chemical segregation control is primordial when producing high value-added materials, such as zirconium alloys for nuclear industry. Vacuum processing allows production very high purity ingot, however it also presents an additional problematic concerning control and prediction of alloy elements evaporation. This PhD dissertation aims at improving prediction of volatile metallic species evaporation during vacuum elaboration, especially during Zircaloy 4 VAR (Vacuum Arc Remelting).First, the evaporation kinetics and the expansion of the metal vapour produced during vacuum melting is investigated. The study is done with a combination of volatilisation experiments using an experimental electron beam furnace and particle based numerical simulation (FPM) of vapour behaviour. Our volatilisation studies on pure metals, Ti and Zr, show the importance of collisions above the liquid on the vapour expansion and its recondensation. Determination of Fe and Sn vapour expansion during Zy4 vacuum melting combined with particle simulation, allowed us to determine thermodynamic activity coefficients values for these elements in liquid Zy4.Then, metallic vapour expansion under VAR conditions is studied, with particular interest shown to condensation flows on the different surfaces. Application of our numerical model to Zy4 shows that the vapour deposited on the mould has a very different composition compared to the alloy. Finally, the particle model is coupled to an ingot growth model and we study the influence of evaporation, condensation and crown reincorporation with regard to volatile solute segregation and depletion. This coupling also provides a first prediction of crown thickness and composition and we compare them to industrial crown samples
Ghazal, Ghassan. « Etude de la propreté inclusionnaire des lingots VAR - Application aux alliages de titane ». Thesis, Vandoeuvre-les-Nancy, INPL, 2010. http://www.theses.fr/2010INPL016N/document.
Texte intégralThe presence of exogeneous inclusions has always been a major concern for the titanium industry. To help improve the inclusional cleanliness of VAR (Vacuum Arc Remelting) titanium ingots, a numerical and experimental study was undertaken.The numerical model is capable of predicting the motion and dissolution of a hard-α defect falling from the electrode tip into the ingot melt pool during vacuum arc remelting. It is implemented in SOLAR, a CFD code that simulates the ingot growth and solidification. The dissolution of the inclusion is governed by nitrogen diffusion from the defect towards the surrounding molten metal. A model describing this phenomenon predicts the particle size evolution and the nitrogen profile at each moment. The motion of the spherical particle is tracked using a Lagrangian model and the influence of turbulence is accounted for by a modification of the drag coefficient.Results show that inclusion removal is difficult with a single melt since the growth of a β-phase layer leads to an initial increase in the defect size. The inclusion behaviour is highly dependent on the pool hydrodynamics and on inclusion characteristics.In order to clarify dissolution aspects of these defects and to measure their dissolution kinetics, synthetically processed defects were introduced into molten titanium heated in an electron beam melting furnace. Dissolution rates were calculated by measuring the size of the defects before and after the experiments and the results were used to validate the numerical models. Furthermore, the experiments show that dissolution kinetics highly depend on fluid motion and temperature