scholarly journals A Simplified Scaling Law of Cell-Dendrite Transition in Directional Solidification

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Yaochan Zhu ◽  
Hua Qiu ◽  
Zhijun Wang ◽  
Eckart Schnack
Keyword(s):  
Directional Solidification ◽  
Phase Field ◽  
Thermal Gradient ◽  
Scaling Law ◽  
Primary Spacing ◽  
Cell Dendrite ◽  
Quantitative Phase ◽  
Physical Foundation ◽  
Pulling Velocity

To describe the cell-dendrite transition (CDT) during directional solidification, a new simplified scaling law is proposed and verified by quantitative phase field simulations. This scaling law bears clear physical foundation with consideration of the overall effects of primary spacing, pulling velocity, and thermal gradient on the onset of sidebranches. The analysis results show that the exponent parameters in this simplified scaling law vary within different systems, which mediates the discrepancy of exponent parameters in previous experiments. The scaling law also presents an explanation for the destabilizing mechanism of thermal gradient in sidebranching dynamics.

Tilted Dendritic Growth Dynamics and Dendrite to Degenerate Seaweed Transition in Directional Solidification: Insights from Phase-Field Simulations

2018 ◽  
Vol 15 ◽  
pp. 128-153
Author(s):  
Hui Xing ◽  
Xiang Lei Dong ◽  
Jian Yuan Wang ◽  
Ke Xin Jin
Keyword(s):  
Directional Solidification ◽  
Misorientation Angle ◽  
Phase Field ◽  
Dendritic Growth ◽  
Growth Dynamics ◽  
Growth Direction ◽  
Primary Spacing ◽  
Stability Range ◽  
Spacing Selection ◽  
Pulling Velocity

In this paper, we review our results from phase field simulations of tilted dendritic growth dynamics and dendrite to seaweed transition in directional solidification of a dilute alloy. We focus on growth direction selection, stability range and primary spacing selection, and degenerate seaweed-to-tilted dendrite transition in directional solidification of non-axially orientated crystals. For growth direction selection, the DGP law (Phys. Rev. E, 78 (2008) 011605) was modified through take the anisotropic strength and pulling velocity into account. We confirm that the DGP law is only validated in lower pulling velocity. For the stability range and primary spacing selection, we found that the lower limit of primary spacing is irrelative to the misorientation angle but the upper limit is nonlinear with respect to the misorientation angle. Moreover, predicted results confirm that the power law relationship with the orientation correction by Gandin et al. (Metall. Mater. Trans. A. 27A (1996) 2727-2739) should be a universal scaling law for primary spacing selection. For the seaweed-to-dendrite transition, we found that the tip-splitting instability in degenerate seaweed growth dynamics is related to the M-S instability dynamics, and this transition originates from the compromise in competition between two dominant mechanisms, i.e., the macroscopic thermal field and the microscopic interfacial energy anisotropy.

The Diffusion and Solid-Liquid Phase Transformation in Directional Solidification of Alloy: A Quantitative Phase Field Characterization and Real-Time Observation

2018 ◽  
Vol 15 ◽  
pp. 97-127
Author(s):  
Yun Chen ◽  
Na Min Xiao ◽  
Dian Zhong Li ◽  
Tong Zhao Gong ◽  
Henri Nguyen-Thi
Keyword(s):  
Directional Solidification ◽  
Real Time ◽  
Phase Field ◽  
Rapid Development ◽  
Adaptive Finite Element Method ◽  
Quantitative Phase ◽  
Diffusion Limited ◽  
Time Observation ◽  
Solid Liquid ◽  
Real Time Observation

Directional solidification is a paradigm process to gain the desired microstructure via certain applied solidification parameters. A thorough understanding of the diffusion-limited solid-liquid interface morphology evolution from initial transient to steady state is of uppermost importance to optimize the solidification processes. The rapid development of quantitative phase-field model provides a feasible computational tool to explore the underlying physics of the morphological transition at different stages. On basis of the diffusion-limited quantitative phase-field simulations using adaptive finite element method, the directional solidification of Al-4wt.%Cu alloy is characterized and both the solid interface propagation speed and solute profile are analyzed. The simulations are then compared with the in situ and real-time observation by means of synchrotron radiation x-ray radiography image. Good agreements are obtained between simulations and experimental data. Detailed mechanism that controls the morphological instability and transition are then addressed.

Simulation of Bridgman Directional Solidification Microstructure Using Phase Field Method

2013 ◽  
Vol 652-654 ◽  
pp. 2437-2440
Author(s):  
Chunhua Tang ◽  
Jin Jun Tang ◽  
Cui Liang
Keyword(s):  
Grain Boundary ◽  
Directional Solidification ◽  
Phase Field ◽  
Field Method ◽  
Planar Interface ◽  
Solidification Microstructure ◽  
Phase Field Method ◽  
Initial Stage ◽  
Last Stage ◽  
Pulling Velocity

In this paper, the directional solidification microstructure of Bridgman system was simulated using phase-field method, and different calculated results were obtained with four pulling velocities. When the pulling velocity is 0.06 cm/s, the columnar crystals competitively grow in the initial stage, and have a necking phenomenon in the last stage. When the pulling velocity is 0.04 cm/s, the columnar crystals become thinner and competitively grow all the time, and the microsegregation is bigger. When the pulling velocity is 1.00 cm/s, planar interface comes back, and solute trapping takes place. The columnar crystals become much thinner, and microsegregation decreases. When the pulling velocity is 3.00 cm/s, the grain boundary of columnar crystals becomes unconspicuous, and the degree of microsegregation approaches 1.

Primary spacing in directional solidification

1998 ◽  
Vol 29 (13) ◽  
pp. 1113-1119 ◽  
Author(s):  
Dexin Ma ◽  
Peter R. Sahm
Keyword(s):  
Directional Solidification ◽  
Primary Spacing

Cooling Process for Directional Solidification in Directed Energy Deposition

2018 ◽  
Author(s):  
Keiya Ishiyama ◽  
Ryo Koike ◽  
Yasuhiro Kakinuma ◽  
Tetsuya Suzuki ◽  
Takanori Mori
Keyword(s):  
Directional Solidification ◽  
Thermal Gradient ◽  
Large Scale ◽  
Energy Deposition ◽  
Production Efficiency ◽  
Production Costs ◽  
Special Structure ◽  
Mechanical Stiffness ◽  
Directed Energy Deposition ◽  
Directed Energy

Additive manufacturing (AM) for metals has attracted attention from industry because of its great potential to enhance production efficiency and reduce production costs. Directed energy deposition (DED) is a metal AM process suitable to produce large-scale freeform metal products. DED entails irradiating the baseplate with a laser beam and launching the metal powder onto the molten spot to produce a metal part on the baseplate. Because the process enables powder from different materials to be used, DED is widely applicable to valuable production work such as for a dissimilar material joint, a graded material, or a part with a special structure. With regard to parts with a special structure, directional solidification can prospectively be used in the power plant and aerospace industries because it can enhance the stiffness in a specific direction via only a simple process. However, conventional approaches for directional solidification require a special mold in order to realize a long-lasting thermal gradient in the part. On the other hand, from the viewpoint of thermal distribution in a produced part, DED is able to control the gradient by controlling the position of the molten pool, i.e., the position of the laser spot. Moreover, unlike casting, the thermal gradient can be precisely oriented in the expected direction, because the laser supplies heat energy on the regulated spot. In this study, the applicability of DED to directional solidification in Inconel® 625 is theoretically and experimentally evaluated through metal structure observation and Vickers hardness measurements. Furthermore, the effect of two different cooling processes on directional solidification is also considered with the aim of improving the mechanical stiffness of a part produced by DED. The observations and experimental results show that both the cooling methods (baseplate cooling and intermittent treatment with coolant) are able to enhance the hardness while retaining the anisotropy.

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