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The deviation from eutectic composition in boundary layer for eutectic growth: a phase-field study

Tu Zhixin, Zhou Jianxin, Yin Yajun, Ji Xiaoyuan, Shen Xu

Archives of Metallurgy and Materials

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2019

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Vol. 64, iss. 1

119--123

EN

In this paper, the deviation from eutectic composition in boundary layer for eutectic growth is studied by phase-field method. According to a series of artificial phase diagram, the lamellar eutectic growth of these alloy is simulated during directional solidification. At steady state, average growth velocity of eutectic lamella is equal to the pulling velocity. With the increasing of the liquidus slope of β phase, the average composition in boundary layer would deviate from eutectic composition and the deviation increases. The constitutional undercooling difference between both solid phases caused by the deviation increases with the increasing of the deviation. The β phase would develop a depression under the influence of the deviation.

2

Modification Mechanism and Growth Process of Al3(Sc, Zr) Particles in As-cast Al-Si-Mg-Cu-Zr-Sc Alloy

Li Y., Du X., Fu J., Zhang Y., Zhang Z., Zhou S., Wu Y.

Archives of Foundry Engineering

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2018

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Vol. 18, iss. 2

51--56

EN

In this study, the modification mechanism and growth process of Al3(Sc, Zr) particles in as-cast Al-Si-Mg-Cu based alloy with addition of Sc and Zr were systematically investigated. It was found that 0.57 wt-%Sc addition caused a significant refinement in the average grain size of the investigated alloy, which brought about a remarkable transformation in as-cast microstructure, from thick dendritic shape to fine equiaxed structure. A large amount of primary Al3(Sc, Zr) particles with the dimension of around 5-6 μm were also observed within the equiaxed grain. Due to the identical orientation and similar crystal structure between primary Al3(Sc, Zr) particles and α-Al matrix, the primary particles always served as heterogeneous nucleus for the α-Al matrix. In addition, these cusped cubic primary Al3(Sc, Zr) particles showed triangle, star, rhomboid morphologies are generated from sectioning the particle in (111), (100) and (110) planes, respectively. Particularly, the typical eutectic structure which contained odd number-layer (Al3(Sc, Zr)+α-Al+ ... +Al3(Sc, Zr)) was observed within the investigated particles.

3

Modeling of Eutectic Formation in Al-Si Alloy Using A Phase-Field Method

Ebrahimi Z.

Archives of Metallurgy and Materials

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2017

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Vol. 62, iss. 4

1969--1981

EN

We have utilized a phase-field model to investigate the evolution of eutectic silicon in Al-Si alloy. The interfacial fluctuations are included into a phase-field model of two-phase solidification, as stochastic noise terms and their dominant role in eutectic silicon formation is discussed. We have observed that silicon spherical particles nucleate on the foundation of primary aluminum phase and their nucleation continues on concentric rings, through the Al matrix. The nucleation of silicon particles is attributed to the inclusion of fluctuations into the phase-field equations. The simulation results have shown needle-like, fish-bone like and flakes of silicon phase by adjusting the noise coefficients to larger values. Moreover, the role of primary Al phase on nucleation of silicon particles in Al-Si alloy is elaborated. We have found that the addition of fluctuations plays the role of modifiers in our simulations and is essential for phase-field modeling of eutectic growth in Al-Si system. The simulated finger-like Al phases and spherical Si particles are very similar to those of experimental eutectic growth in modified Al-Si alloy.

4

Cellular automata modeling of cooperative eutectic growth

Burbelko A., Gurgul D., Fraś E., Olejnik E.

Archives of Foundry Engineering

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2010

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Vol. 10, iss. 1 spec.

29--34

EN

The model and results of the 2D simulation of the cooperative growth of two phases in the lamellar eutectic are presented. The proposed model takes into account heat transfer, components diffusion and nonstationary concentration distribution in the liquid and solid phases, non-equlibrium nature of the phase transformation and kinetics of the growth, influence of the surface energy and interface curvature on the conditions of the thermodynamic equilibrium. For the determination of the phase interface shape the Cellular Automata technique (CA) was used. For the calculation of temperature and concentration distribution the numerical solution of the Fourier equation was used. The partial differential equations were solved by Finite Differences Method (FDM). The spatial position and cell sizes of CA lattice and FDM mesh are equal. Proposed model can predict the steady state growth with a constant interlamellar spacing in the regular plate eutectic, as well as some transient processes that bring to the changes of that parameters. Obtained simulation data show the solid-liquid interface changes result in the termination of lamella and enlargement of interlamellar spacing. Another simulation results illustrate a pocket formation in the center of one phase that forestalls nucleation (or intergrowth) of the new lamellae of another phase. The data of the solidification study of the transparent material (CBr4– 8,4% C2Cl6) obtained in the thin layer demonstrate the qualitative agreement of the simulation.

5

Analiza czynników wpływających na krystalizację eutektyki w stopie AI-Cu-Ag

Nocuń S., Konopka Z., Zyska A., Łągiewka M., Bober A.

Archiwum Odlewnictwa

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2006

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R. 6, nr 22

338-343

PL

Praca przedstawia analizę czynników determinujących rodzaj eutektyki podwójnej AI-Al_{2}Cu w potrójnym stopie AI-Cu-Ag. Czynniki jakie były analizowane to: entropia rozpuszczania faz eutektycznych, ułamek objętościowy danej fazy eutektycznej, prędkość wzrostu i gradient temperatury.

EN

In this paper it was shown the influence of the parameters such as: entropy of fusion, volume fraction, velocity of the unidirectional solidification on the lamellar eutectic obtained during unidirectional solidification. It was shown that all known parameters allow us to classify obtained eutectic into regular lamellar eutectic what was proven during the microscopy observations shown on the figure 1. There is also shown the disturbances occurred during increasing the velocity of the unidirectional solidification - shown on the figure 2. It can be estimated that this disturbances are occurred by evolution of the lamellar structure into the rod eutectic, or even loosing the regularity of the structure.