First analysis of a numerical benchmark for 2D columnar solidification of binary alloys

International audienceDuring the solidification of metal alloys, chemical heterogeneities at the product scale (macrosegregation) develop. Numerical simulation tools are beginning to appear in the industry, however their predictive capabilities are still limited. We present a numerical benchmark exercise treating the performance of models in the prediction of macrosegregation. In a first stage we defined a "minimal" (i.e. maximally simplified) solidification model, describing the coupling of the solidification of a binary alloy and of the transport phenomena (heat, solute transport and fluid flow) that lead to macrosegregation in a fully columnar ingot with a fixed solid phase. This model is solved by four different numerical codes, employing different numerical methods (FVM and FEM) and various solution schemes. We compare the predictions of the evolution of macrosegregation in a small (10×6 cm) ingot of Sn-10wt%Pb alloys. Further, we present the sensitivities concerning the prediction of instabilities leading to banded channel mesosegregations

Formation of intermetallic phases in AlSi7Fe1 alloy processed under microgravity and forced fluid flow conditions and their influence on the permeability

Ternary Al-6.5wt.%Si-0.93wt.%Fe alloy samples were directionally solidified on-board of the International Space Station ISS in the ESA payload Materials Science Laboratory (MSL) equipped with Low Gradient Furnace (LGF) under both purely diffusive and stimulated convective conditions induced by a rotating magnetic field. Using different analysis techniques the shape and distribution of the intermetallic phase β-Al 5 SiFe in the dendritic microstructure was investigated, to study the influence of solidification velocity and fluid flow on the size and spatial arrangement of intermetallics. Deep etching as well as 3-dimensional computer tomography measurements characterized the size and the shape of β-Al 5 SiFe platelets: Diffusive growth results in a rather homogeneous distribution of intermetallic phases, whereas forced flow promotes an increase in the amount and the size of β-Al 5 SiFe platelets in the centre region of the samples. The β-Al 5 SiFe intermetallics can form not only simple platelets, but also be curved, branched, crossed, interacting with dendrites and porosity located. This leads to formation of large and complex groups of Fe-rich intermetallics, which reduce the melt flow between dendrites leading to lower permeability of the mushy zone and might significantly decrease feeding ability in castings

NUMERICAL SIMULATIONS OF TURBULENT FLOW IN THE ELECTROMAGNETICALLY LEVITATED METALLIC DROPLET

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Numerical simulations of turbulent flow in an electromagnetically levitated metallic droplet using k-Ω SST and Reynolds stress models

International audienceElectromagnetic levitation of a metallic droplet in the microgravity conditions is modelled accounting for the droplet shape variation, its displacement and turbulent character of the flow in the system. Three different models are applied for description of turbulent flow in the droplet: k − ω SST model and two models based on Reynolds stresses (RSM), all of them resulted in a qualitatively similar flow inside a droplet. Use of RSM-based models leads to a sharper interface of a droplet in volume-of-fluid calculations compared to the k − ω SST model. Two RSM models predict value of the surface tension close to a theoretical one, yet, both fail in predicting of viscosity of the droplet's material

Sciences physiques en microgravité au sein du GDR Micropesanteur Fondamentale et Appliquée

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NUMERICAL SIMULATIONS OF TURBULENT FLOW IN THE ELECTROMAGNETICALLY LEVITATED METALLIC DROPLET

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Numerical modelling of heat transfers between inductively heated metallic and dielectric phases

International audienceHeating with a low-frequency induction is a key phenomenon in a process dedicated to the treatment of nuclear wastes. This papers presents a step of the numerical model being developed in order to study this process. A hydrodynamic model for the processing of a liquid charge consisting of a metallic phase and a dielectric one is developed based on a Volume Of Fluid approach coupled with electromagnetic calculations. The latter allows one to calculate the distribution of the Joule heating in the setup and radiative heat exchange inside the crucible is accounted with a Surface-To-Surface (S2S) model coupled with VOF. Numerical results are compared with the measures obtained on the prototype of the process. The results are in good agreement but the model needs to be improved in order to consider the varying viscosity of the glass. The usage of a radiation model coupled to the VOF model is not common for studies of materials melted by electromagnetic induction. This paper demonstrate the feasibility of this approach

FEM Magneto-thermo-electric modeling around a solid grain during alloy solidification under uniform AC/DC magnetic field

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