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Y. A. Chang - One of the best experts on this subject based on the ideXlab platform.
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Microstructure and Microsegregation in directionally solidified Mg–4Al alloy
Intermetallics, 2007Co-Authors: Chuan Zhang, K.-s. Wu, Dong Ma, Y. A. ChangAbstract:Abstract Directional solidification (DS) of a binary Mg–4Al (wt.%) alloy was carried out to investigate the microstructures and Microsegregation under controlled solidification conditions. In directional solidification the microstructure depends on the growth rate V because the cooling rate, which governs the solidification microstructure, is the product of the growth rate and the temperature gradient. The ability to produce simple and uniform microstructures in directional solidification enables us to correlate the formation of the microstructure and its characteristic length scales quantitatively with processing parameters. The morphology of the solid–liquid interface and the microstructure of both the mushy zone and the steady-state region were characterized at different levels of growth rates. With the help of an electron microprobe, Microsegregation was determined in a specimen directionally solidified with cooling rates ranging from 0.06 to 0.8 K/s. The calculated Microsegregation results based on the Scheil model deviated significantly from the experimental data, which is anticipated since back diffusion was not included due to the lack of diffusivity data.
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modeling of microstructure and Microsegregation in solidification of multi component alloys
Journal of Phase Equilibria and Diffusion, 2007Co-Authors: Mingfang Zhu, Shuanglin Chen, Weisheng Cao, Chun Pyo Hong, Y. A. ChangAbstract:Driven by industrial demand, extensive efforts have been made to investigate microstructure evolution and Microsegregation development during solidification of multicomponent alloys. This paper briefly reviews the recent progress in modeling of microstructures and Microsegregation in solidification of multicomponent alloys using various models including micromodel, phase field, front tracking, and cellular automaton approaches. A two-dimensional modified cellular automaton (MCA) model coupled with phase diagram software PanEngine is presented for the prediction of microstructures and Microsegregation in the solidification of ternary alloys. The model adopts MCA technique to simulate dendritic growth. The thermodynamic data needed for determining the dynamics of dendritic growth are calculated with PanEngine. After validating the model by comparing the simulated values with the prediction of the Scheil model for solute profiles in the primary dendrites as a function of solid fraction, the model was applied to simulate the microstructure and Microsegregation in the solidification of Al-rich ternary alloys. The simulation results demonstrate the capabilities of the present model not only to simulate realistic dendrite morphologies, but also to predict quantitatively the Microsegregation profiles in the solidification of multi-component alloys.
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computational and experimental investigation of Microsegregation in an al rich al cu mg si quaternary alloy
Acta Materialia, 2002Co-Authors: Xinyan Yan, Shuanglin Chen, Fanyou Xie, Y. A. ChangAbstract:Abstract A new micromodel was developed to predict the microstructure and Microsegregation in multicomponent alloys during dendritic solidification. The micromodel was directly coupled with multicomponent phase diagram calculations using a user friendly and robust phase diagram calculation engine—PanEngine. Solid back diffusion, undercooling and coarsening effects were included in this model, and the experimentally measured cooling curves were used as the inputs to carry out the Microsegregation calculations. Microsegregation in Al–4.5 wt%Cu–1 wt%Si–0.5 wt%Mg alloy was experimentally investigated from directional solidification and electron probe microanalysis. Calculated results using this model are in accord with the experimental data, while results from the Scheil model deviate significantly from the experimental data.
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Microsegregation in al 4 5cu wt alloy experimental investigation and numerical modeling
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: Xinyan Yan, Fanyou Xie, M G Chu, Y. A. ChangAbstract:Abstract Microsegregation in Al–4.5 wt.%Cu alloy was investigated experimentally using directional solidification and electron probe microanalysis (EPMA). The degrees of dendrite tip undercooling were measured for growth rates from 0.0038 to 0.2 mm s−1 with a temperature gradient of 50°C cm−1 at the liquid–solid interfaces. A modified Scheil model incorporating back diffusion, undercooling and dendrite arm coarsening was used to calculate the degrees of Microsegregation. The partition coefficients obtained from the thermodynamic models of the solid and liquid phases and the measured cooling curves were used as the inputs to carry out the Microsegregation calculation. While the calculated results using the Scheil model deviate significantly from the experimental data, those from the modified Scheil model are much better. Out of the three geometrical models, i.e. plate, sphere and cylinder, to approximate the shapes of the dendrites, the sphere is the best. However, the calculated results using the spherical model is near accord with the data for small fractions of solids and those using the cylinder is better at large fractions of solids. Two different thermodynamic descriptions of the Al–Cu system were used to demonstrate the importance of reliable phase diagram data in studying the degree of Microsegregation.
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importance of reliable phase equilibria in studying Microsegregation in alloys al cu mg
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: H Liang, T Kraft, Y. A. ChangAbstract:Abstract The solid and liquid phase equilibrium of Al-rich Al–Cu and Al–Cu–Mg alloys was investigated in order to examine the effect of small uncertainties in the solidus on model-calculated Microsegregation during solidification. The phase boundaries were determined using EPMA on quenched two-phase alloys. The liquidus was obtained using a raster beam scan technique. The phase boundaries obtained for Al–Cu are in accord with experimental data available in the literature. The measured (Al) solidus in terms of Cu is found to be ∼0.5 at% higher than model-calculated values from a thermodynamic description reported in the literature. On the other hand, the measured (Al) liquidus in terms of Cu are in good agreement with model-calculations. Moreover, the difference between the measured and calculated solidus in ternary Al–Cu–Mg was found to be the same as that in binary Al–Cu. This difference is believed to be responsible for the deviations in the calculated Microsegregation from experimental data for Al-rich Al–Cu–Mg alloys. The (Al ) phase in both the Al–Cu and Al–Cu–Mg systems was thus remodeled so that the calculated solidus using the new model description is in better agreement with experimental data. The Microsegregation model-calculations show that even small differences in the phase boundaries of 0.5 at.% or less have a pronounced effect on the calculated concentration profiles of Cu in the dendrites. We thus conclude that in order to test the validity of a Microsegregation model, accurate phase boundary data are needed!
Zhongming Ren - One of the best experts on this subject based on the ideXlab platform.
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Evolution of Microsegregation in directionally solidified Al–Cu alloys under steady magnetic field
Journal of Alloys and Compounds, 2019Co-Authors: Rui Guo, Weidong Xuan, Jiang Wang, Zhongming RenAbstract:Abstract Experimental investigations on Microsegregation during directional solidification of two Al–Cu alloys with and without a steady magnetic field (SMF) were carried out. The solidification morphologies and Microsegregation behaviors were examined. The amount of non-equilibrium eutectics and the concentration versus solid fraction profiles were obtained. The results indicated that the amount of Microsegregation was increased under an SMF when the solid/liquid interface was planar. For cellular and dendritic growth, however, the SMF alleviated the Microsegregation level. The change of the factors affecting Microsegregation under the SMF was analyzed. The reduction in solid diffusion coefficient in an SMF aggravated the Microsegregation level, while the thermoelectric magnetic convection (TEMC) was found to have a positive effect. It was concluded that the change in Microsegregation in different conditions might be attributed to the combined action of solid diffusion suppression and TEMC in mushy zone under an SMF. Based on Brody model, the Microsegregation behavior in an SMF was predicted. The calculated results were in agreement with experiment observations.
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Evolution of microstructure and Microsegregation in Ni-Mn-Ga alloys directionally solidified under axial magnetic field
Journal of Alloys and Compounds, 2018Co-Authors: Long Hou, Zhongming Ren, Yanchao Dai, Yves Fautrelle, Claude EslingAbstract:In this work, the microstructure and Microsegregation in Ni-Mn-Ga alloys directionally solidified using a seedless Bridgman technique under an axial magnetic field are investigated. The experimental results indicate that the magnetic field refines cells/dendrites and reduces Microsegregation. A numerical simulation is performed to investigate convection during directional solidification under an axial magnetic field. Thermoelectric magnetic convection at the cell/dendrite scale is found to be primarily responsible for the refinement of cells/dendrites and for the inter-cellular/dendritic composition homogeneity under a magnetic field. This finding is of significance as it highlights the role of magnetic field on the Microsegregation during directional solidification, which could be used in future as a tool for controlled microstructure growth.
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formation mechanism of axial macrosegregation of primary phases induced by a static magnetic field during directional solidification
Scientific Reports, 2017Co-Authors: Yves Fautrelle, Zhongming Ren, Rene MoreauAbstract:Understanding the macrosegregation formed by applying magnetic fields is of high commercial importance. This work investigates how static magnetic fields control the solute and primary phase distributions in four directionally solidified alloys (i.e., Al-Cu, Al-Si, Al-Ni and Zn-Cu alloys). Experimental results demonstrate that significant axial macrosegregation of the solute and primary phases (i.e., Al2Cu, Si, Al3Ni and Zn5Cu phases) occurs at the initial solidification stage of the samples. This finding is accompanied by two interface transitions in the mushy zone: quasi planar → sloping → quasi planar. The amplitude of the macrosegregation of the primary phases under the magnetic field is related to the magnetic field intensity, temperature gradient and growth speed. The corresponding numerical simulations present a unidirectional thermoelectric (TE) magnetic convection pattern in the mushy zone as a consequence of the interaction between the magnetic field and TE current. Furthermore, a model is proposed to explain the peculiar macrosegregation phenomenon by considering the effect of the forced TE magnetic convection on the solute distribution. The present study not only offers a new approach to control the solute distribution by applying a static magnetic field but also facilitates the understanding of crystal growth in the solute that is controlled by the static magnetic field during directional solidification.
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influence of an axial uniform magnetic field on the solid liquid interface curvature and macrosegregation in directionally solidified the al 0 85 wt cu alloy
Materials Letters, 2011Co-Authors: Zhongming Ren, Guanghui Cao, Annie Gagmoud, Yves FautrelleAbstract:Abstract Effect of a uniform magnetic field on the solid/liquid interface curvature and macrosegregation in directionally solidified the Al–0.85 wt.% Cu alloy has been investigated. Results show that the interface curvature and macrosegregation increase to a maximum when B is about 0.1 T; and then decreases as B still increases. This is good agreement with the computed velocities of the thermoelectric magnetic convection. Above results reveal that the uniform magnetic field induces the new convection and further modifies the interface curvature and macrosegregation.
Fanyou Xie - One of the best experts on this subject based on the ideXlab platform.
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computational and experimental investigation of Microsegregation in an al rich al cu mg si quaternary alloy
Acta Materialia, 2002Co-Authors: Xinyan Yan, Shuanglin Chen, Fanyou Xie, Y. A. ChangAbstract:Abstract A new micromodel was developed to predict the microstructure and Microsegregation in multicomponent alloys during dendritic solidification. The micromodel was directly coupled with multicomponent phase diagram calculations using a user friendly and robust phase diagram calculation engine—PanEngine. Solid back diffusion, undercooling and coarsening effects were included in this model, and the experimentally measured cooling curves were used as the inputs to carry out the Microsegregation calculations. Microsegregation in Al–4.5 wt%Cu–1 wt%Si–0.5 wt%Mg alloy was experimentally investigated from directional solidification and electron probe microanalysis. Calculated results using this model are in accord with the experimental data, while results from the Scheil model deviate significantly from the experimental data.
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Microsegregation in al 4 5cu wt alloy experimental investigation and numerical modeling
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2001Co-Authors: Xinyan Yan, Fanyou Xie, M G Chu, Y. A. ChangAbstract:Abstract Microsegregation in Al–4.5 wt.%Cu alloy was investigated experimentally using directional solidification and electron probe microanalysis (EPMA). The degrees of dendrite tip undercooling were measured for growth rates from 0.0038 to 0.2 mm s−1 with a temperature gradient of 50°C cm−1 at the liquid–solid interfaces. A modified Scheil model incorporating back diffusion, undercooling and dendrite arm coarsening was used to calculate the degrees of Microsegregation. The partition coefficients obtained from the thermodynamic models of the solid and liquid phases and the measured cooling curves were used as the inputs to carry out the Microsegregation calculation. While the calculated results using the Scheil model deviate significantly from the experimental data, those from the modified Scheil model are much better. Out of the three geometrical models, i.e. plate, sphere and cylinder, to approximate the shapes of the dendrites, the sphere is the best. However, the calculated results using the spherical model is near accord with the data for small fractions of solids and those using the cylinder is better at large fractions of solids. Two different thermodynamic descriptions of the Al–Cu system were used to demonstrate the importance of reliable phase diagram data in studying the degree of Microsegregation.
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microstructure and Microsegregation in al rich al cu mg alloys
Acta Materialia, 1999Co-Authors: Fanyou Xie, T Kraft, Y Zuo, C H Moon, Y. A. ChangAbstract:Abstract Microstructure and Microsegregation in two directionally solidified Al alloys, Al–3.9Cu–0.9Mg and Al–15Cu–1Mg (in wt%), were investigated for cooling rates between 0.78 and 0.039 K/s. Transverse and longitudinal sections were examined to exhibit dendritic microstructures. Fractions of solids formed were determined using quantitative image analysis and solute redistribution in the primary phase was determined using area scans. The model employed to calculate Microsegregation is based on the Scheil model but including solid-state diffusion, dendrite arm coarsening and undercooling of the dendrite tip and the formation of eutectic. The model-calculated results were found to be in good agreement with the experimentally determined concentration distributions in the primary α phase and the amounts of phases formed. It was found that the dendrite morphology was best described by a cylindrical arm geometry and that the accuracy of the phase diagram could have a significant influence on the Microsegregation predictions. For the alloy with low copper content, two types of embedded droplets were observed.
T Kraft - One of the best experts on this subject based on the ideXlab platform.
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importance of reliable phase equilibria in studying Microsegregation in alloys al cu mg
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2000Co-Authors: H Liang, T Kraft, Y. A. ChangAbstract:Abstract The solid and liquid phase equilibrium of Al-rich Al–Cu and Al–Cu–Mg alloys was investigated in order to examine the effect of small uncertainties in the solidus on model-calculated Microsegregation during solidification. The phase boundaries were determined using EPMA on quenched two-phase alloys. The liquidus was obtained using a raster beam scan technique. The phase boundaries obtained for Al–Cu are in accord with experimental data available in the literature. The measured (Al) solidus in terms of Cu is found to be ∼0.5 at% higher than model-calculated values from a thermodynamic description reported in the literature. On the other hand, the measured (Al) liquidus in terms of Cu are in good agreement with model-calculations. Moreover, the difference between the measured and calculated solidus in ternary Al–Cu–Mg was found to be the same as that in binary Al–Cu. This difference is believed to be responsible for the deviations in the calculated Microsegregation from experimental data for Al-rich Al–Cu–Mg alloys. The (Al ) phase in both the Al–Cu and Al–Cu–Mg systems was thus remodeled so that the calculated solidus using the new model description is in better agreement with experimental data. The Microsegregation model-calculations show that even small differences in the phase boundaries of 0.5 at.% or less have a pronounced effect on the calculated concentration profiles of Cu in the dendrites. We thus conclude that in order to test the validity of a Microsegregation model, accurate phase boundary data are needed!
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microstructure and Microsegregation in al rich al cu mg alloys
Acta Materialia, 1999Co-Authors: Fanyou Xie, T Kraft, Y Zuo, C H Moon, Y. A. ChangAbstract:Abstract Microstructure and Microsegregation in two directionally solidified Al alloys, Al–3.9Cu–0.9Mg and Al–15Cu–1Mg (in wt%), were investigated for cooling rates between 0.78 and 0.039 K/s. Transverse and longitudinal sections were examined to exhibit dendritic microstructures. Fractions of solids formed were determined using quantitative image analysis and solute redistribution in the primary phase was determined using area scans. The model employed to calculate Microsegregation is based on the Scheil model but including solid-state diffusion, dendrite arm coarsening and undercooling of the dendrite tip and the formation of eutectic. The model-calculated results were found to be in good agreement with the experimentally determined concentration distributions in the primary α phase and the amounts of phases formed. It was found that the dendrite morphology was best described by a cylindrical arm geometry and that the accuracy of the phase diagram could have a significant influence on the Microsegregation predictions. For the alloy with low copper content, two types of embedded droplets were observed.
Hervé Combeau - One of the best experts on this subject based on the ideXlab platform.
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effect of the coriolis force on the macrosegregation of aluminum in the centrifugal casting of ti al alloys
IOP Conference Series: Materials Science and Engineering, 2019Co-Authors: Cisternas M Fernandez, Hervé Combeau, Miha Založnik, Julien Zollinger, Chunmei Huang, U HechtAbstract:Within the framework of the ESA GRADECET project, experiments of directional solidification of cylindrical Ti-Al samples were conducted in hypergravity. The experiments were performed in a centrifuge with the apparent gravity (sum of centrifugal and terrestrial gravity) aligned along the cylinder centerline. 3D numerical simulations of aluminum macrosegregation in these samples are presented. A volume-averaging solidification model is used that accounts for centrifugal and Coriolis accelerations in a non-inertial rotating reference system. We compare the melt flow pattern and the macrosegregation formation under terrestrial gravity and under centrifugation. The results show that the Coriolis acceleration, although very weak, breaks the symmetry of the thermosolutal convection, having an important impact on the final macrosegregation pattern. The macrosegregation is entirely modified in comparison with a sample solidified under terrestrial gravity conditions. Besides the aluminum segregation intensity increases with the centrifugation level.
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Microsegregation macrosegregation and related phase transformations in tial alloys
Intermetallics, 2011Co-Authors: D Daloz, Hervé Combeau, U Hecht, Julien Zollinger, Alain Hazotte, Miha ZaložnikAbstract:Abstract In the first part of the paper the influences of Microsegregation on the microstructure establishment in Ti–Al based alloys are described. Examples are taken concerning the primary solidification phase, the grain refinement through boron addition, the occurrence of B2 phase in as-cast parts and the link between Microsegregation and creep properties. In the second part, a numerical model of macrosegregation devoted to centrifugal casting of TiAl alloys is presented and the influences of the parameters of the model are discussed.
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prediction of macrosegregation in steel ingots influence of the motion and the morphology of equiaxed grains
Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science, 2009Co-Authors: Hervé Combeau, Miha Založnik, Stephane Hans, Pierre Emmanuel RichyAbstract:Although a significant amount of work has already been devoted to the prediction of macrosegregation in steel ingots, most models considered the solid phase as fixed. As a result, it was not possible to correctly predict the macrosegregation in the center of the product. It is generally suspected that the motion of the equiaxed grains is responsible for this macrosegregation. A multiphase and multiscale model that describes the evolution of the morphology of the equiaxed crystals and their motion is presented. The model was used to simulate the solidification of a 3.3-ton steel ingot. Computations that take into account the motion of dendritic and globular grains and computations with a fixed solid phase were performed, and the solidification and macrosegregation formation due to the grain motion and flow of interdendritic liquid were analyzed. The predicted macrosegregation patterns are compared to the experimental results. Most important, it is demonstrated that it is essential to consider the grain morphology, in order to properly model the influence of grain motion on macrosegregation. Further, due to increased computing power, the presented computations could be performed using finer computational grids than was possible in previous studies; this made possible the prediction of mesosegregations, notably A segregates.
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a new model of Microsegregation for macrosegregation computation in multicomponent steels part ii application to fe ni c alloys
Computational Materials Science, 2009Co-Authors: Ludovic Thuinet, Hervé CombeauAbstract:Paper I of this series was dedicated to the theoretical formulation of a new algorithm to calculate Microsegregation in macrosegregation computation. This paper aims to prove that the Microsegregation model is particularly well adapted to be coupled with a macrosegregation code. The application of the model to Fe–Ni–C alloys shows that it provides reliable Microsegregation results with a very limited number of nodes in non trivial cases (coexistence of two different solid phases during the peritectic transformation, multicomponent systems with very different solute diffusion coefficients). The model predicts that ferrite regression during the peritectic transformation occurs in false paraequilibrium conditions. It is not coherent with the assumptions made to simplify the complex treatment of ferrite regression in macrosegregation computation. It is shown that certain assumptions, which are often employed, can significantly modify the calculated value of the liquid density in the mushy zone.
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a new model of Microsegregation for macrosegregation computation in multicomponent steels part i theoretical formulation and algorithm
Computational Materials Science, 2009Co-Authors: Ludovic Thuinet, Hervé CombeauAbstract:Abstract The goal of this paper is to present a new Microsegregation model for multicomponent steels designed to be coupled with a macrosegregation code, which takes into account the thermodynamic equilibriums between phases and the peritectic transformation. Among the great diversity of Microsegregation models available in literature, very few can fulfil all these requirements. If it is the case, some simplifying assumptions must be adopted to increase the time efficiency of the Microsegregation model but this often results in the restriction of its validity. In the model presented in this paper, a numerical approach is used to solve the diffusion equation in each phase, which implies the definition of a Microsegregation mesh, whose number of nodes must be limited to have realistic calculation time by the resulting micro–macro code. To keep the number of nodes low and ensure mass conservation during calculation, an original algorithm is presented in this paper to ensure the stability of the solution, which is not a trivial problem because of the sharp solute gradients at the δ / γ interface during the peritectic transformation.