Comparison of Channel Segregation Formation in Model Alloys and Steels via Numerical Simulations

Cao, Yingnan; Chen, Y.; Li, D. Z.; Liu, H. W.; Fu, Peng

doi:10.1007/s11661-016-3417-7

Cited by 17 publications

(5 citation statements)

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“…Figure 4 shows the solute concentration of Al-Cu alloy at the specific α/L interface (i.e., φ 1 = φ 3 = 0.5). To thoroughly investigate the effect of the buoyancy force, the solute expansion coefficient varied from 10 -4 β c0 to 10 3 β c0 in units of β c0 = ± 7.3 × 10 -3 [21] . With increasing effects of the buoyancy force, the concentration near α/L interface deviated increasingly from that under no-convection condition, and accordingly, the interfacial solute undercooling ΔT c would change to remain compatible with this variation.…”

Section: Discussionmentioning

confidence: 99%

“…A l l s i m u l a t i o n s w e r e p e r f o r m e d u n d e r a c o n s t a n t undercooling 1 K using Al-Cu eutectic alloy, whose physical parameters [18][19][20][21] are provided in Table 1. It should be noted that the solute expansion coefficient β c was negative, which indicates that the larger the concentration, the heavier the system [18] .…”

Section: Materials and Initial Conditionmentioning

confidence: 99%

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Phase-field-lattice Boltzmann study for lamellar eutectic growth in a natural convection melt

2017

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A s one of the most important solidification patterns, eutectic microstructure has been recognized for its significant influence on the ultimate mechanical properties of the materials [1,2] . Since the classical mathematical analysis for the steady-state growth of eutectic alloy was presented by Jackson and Hunt [3] , theoretical studies on eutectic solidification have attracted increasing attention.However, the influence of convection on eutectic growth still lacks sufficient research. Generally, there are two main types of convection considered during the directional solidification of eutectic alloys, i.e., forced convection caused by imposed external fields, and natural convection driven by the solute (or density) difference. Considering that there are many uncertainties in experiments, numerical simulation has become an indispensable way to accurately recover the underlying physics during solidification [4][5][6][7] . Wang et al. [8] performed a Monte-Carlo simulation of eutectic growth with weak convection and found that convection made Abstract: In the present study, the influence of natural convection on the lamellar eutectic growth is determined by a phase-field-lattice Boltzmann study for Al-Cu eutectic alloy. The mass difference resulting from concentration difference led to the fluid flow, and a robust parallel and adaptive mesh refinement algorithm was employed to improve the computational efficiency without any compromising accuracy. Results show that the existence of natural convection would affect the growth undercooling and thus control the interface shape by adjusting the lamellar width. In particular, by alternating the magnitude of the solute expansion coefficient, the strength of the natural convection is changed. Corresponding microstructure patterns are discussed and compared with those under no-convection conditions. the distribution of lamellar spacing more scattered. But beyond that, to the best of our knowledge, there has been no more numerical case to study the effect of convection on eutectic growth. Encouragingly, a robust parallel-adaptive mesh refinement algorithm (Para-AMR) has been developed to efficiently solve the phase field equations including the dendritic [9] and eutectic transitions [10] . The lattice Boltzmann method (LBM) has also emerged with great potential to numerically solve the energy, momentum and mass transport problems by a relaxation to a local equilibrium [11][12][13] . Therefore, it seems reasonable to couple the LBM into eutectic phase-field models to retrieve the interaction of eutectic microstructure and flows.In this work, we coupled the LBM into the developed Para-AMR algorithm to reveal the effect of natural convection on eutectic growth. The phase field model was employed to simulate eutectic evolution while the LBM was for the simultaneous calculation of melt convection. The velocity field near the solid/liquid (S/ L) interface was explored and several key mechanisms were highlighted. In particular, by alternating the magnitude of solute expansion coe...

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Section: Discussionmentioning

confidence: 99%

Section: Materials and Initial Conditionmentioning

confidence: 99%

Phase-field-lattice Boltzmann study for lamellar eutectic growth in a natural convection melt

2017

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“…In the model, the local thermo-solutal balance is assumed to be met at the solid/liquid interface. The model details can be referred to in our previous publication [ 25 ], and here only the conservations of solute, energy and momentum are listed below.…”

Section: Simulation Methods and Modelmentioning

confidence: 99%

Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations

et al. 2021

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Channel segregation (CS) is the most typical defect during solidification of NbTi alloy. Based on numerical simulation and experimental characterizations, we deeply elucidated its characteristics, formation mechanism, effecting factor and prediction criterion. According to acid etching, industrial X-ray transmission imaging, 3D X-ray microtomography and chemical analysis, it was found that in a casing ingot, by He cooling, finer grain size, weaker segregation and slighter CS can be obtained compared with air-cooled ingot. The simulation results of macrosegregation show that CS is caused by the strong natural convection in the mushy zone triggered by the thermo-solutal gradient. Its formation can be divided into two stages including channel initiation and growth. In addition, due to the stronger cooling effect of the He treatment, the interdendritic flow velocity becomes smaller, consequently lowering the positive segregation and CS and improving the global homogenization of the final ingot. Finally, to predict the formation of CS, the Rayleigh number model was proposed and its critical value was found to be 15 in NbTi alloy for the first time. When it is lower than the threshold, CS disappears. It provides an effective tool to evaluate and optimize the solidification parameters to fabricate the homogenized NbTi ingot in engineering practice.

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“…The formation of the channel segregation is related to the flow perturbation or instability in the mushy zone. When the thermal-solutal convection is adequately strong, flow instability occurs; this in turn destabilizes the mushy zone and causes the channel segregation [20].…”

Section: Validation and Mesh Convergence Studymentioning

confidence: 99%

Numerical Simulation of Macrosegregation Caused by Thermal–Solutal Convection and Solidification Shrinkage Using ALE Model

Chen

Shen

2019

Acta Metall. Sin. (Engl. Lett.)

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Solidification shrinkage has been recognized as an important factor for macrosegregation formation. An arbitrary Lagrangian-Eulerian (ALE) model is constructed to predict the macrosegregation caused by thermal-solutal convection and solidification shrinkage. A novel mesh update algorithm is developed to account for the domain change induced by solidification shrinkage. The velocity-pressure coupling between the non-homogenous mass conservation equation and momentum equation is addressed by a modified pressure correction method. The governing equations are solved by the streamline-upwind/ Petrov-Galerkin-stabilized finite element algorithm. The application of the model to the Pb-19.2 wt%Sn alloy solidification problem is considered. The inverse segregation is successfully predicted, and reasonable agreement with the literature results is obtained. Thus, the ALE model is established to be a highly effective tool for predicting the macrosegregation caused by solidification shrinkage and thermal-solutal convection. Finally, the effect of solidification shrinkage is analyzed. The results demonstrate that solidification shrinkage delays the advance of the solidification front and intensifies the segregation.

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Comparison of Channel Segregation Formation in Model Alloys and Steels via Numerical Simulations

Cited by 17 publications

References 50 publications

Phase-field-lattice Boltzmann study for lamellar eutectic growth in a natural convection melt

Phase-field-lattice Boltzmann study for lamellar eutectic growth in a natural convection melt

Characteristics, Mechanism and Criterion of Channel Segregation in NbTi Alloy via Numerical Simulations and Experimental Characterizations

Numerical Simulation of Macrosegregation Caused by Thermal–Solutal Convection and Solidification Shrinkage Using ALE Model

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