Dendrite fragmentation mechanism under forced convection condition by rotating magnetic field during unidirectional solidification of AlSi7 alloy

Zhang, Haijie; Wu, Menghuai; Rodrigues, Christian M. G.; Ludwig, Andreas; Kharicha, Abdellah; Rónaföldi, Arnold; Roósz, András; Veres, Zsolt; Svéda, Mária

doi:10.1016/j.actamat.2022.118391

Cited by 13 publications

(8 citation statements)

References 59 publications

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“…According to state-of-the-art simulations [7][8][9][10], due to the lack of a reliable fragmentation model, the freckles were indirectly predicted through the calculated segregation channels by ignoring the formation of equiaxed grains. In this study, the formation of equiaxed grains via two different fragmentation mechanisms [5,15,19] are numerically investigated. The calculation of flow and solidification in the superalloy casting was coupled with radiation in the Bridgman furnace.…”

Section: Discussionmentioning

confidence: 99%

“…Two fragmentation mechanisms, i.e. flow-and capillary-driven mechanisms, have been considered in the current study, and the calculated flow which indicates that some fragments vanished because of dendrite coarsening (coalescence or remelting) [5].…”

Section: Formation Of Spurious Grains Via Different Fragmentation Mec...mentioning

confidence: 99%

“…The solute-enriched liquid is continuously sucked into the channel. The roots of higher-order sidearms can be remelted by flow-induced solute enrichment or capillary effects [4,5], that is, dendrite fragmentation occurs. Near the open mouth of the segregation channel, small fragments are transported out of the mushy zone by upwelling (upward flow of solute-enriched liquid enclosed in the plume) and finally remelted in the top hot liquid [6].…”

Section: Introductionmentioning

confidence: 99%

“…In this study, a three-phase mixed columnar-equiaxed solidification model [12] was used to simulate the DS of superalloy casting. The model was recently extended to consider flow-and capillary-driven fragmentation mechanisms [5]. The remelting and solidification of the as-formed solid phases (i.e.…”

Section: Introductionmentioning

confidence: 99%

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Numerical study on the formation of spurious grains and freckles during the directional solidification of superalloys

Zhang

Liu

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

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Freckles, a significant issue encountered during the directional solidification of superalloys, are recognised by a trail of equiaxed grains parallel to the direction of gravity accompanied by local eutectic enrichment. In the current study, a mixed-columnar-equiaxed multiphase volume-average solidification model was employed to study the formation of freckles in superalloy casting. Fragments produced via flow-driven and capillary-driven fragmentation mechanisms are considered as the source of spurious grains. The transport and the growth/remelting of the fragments are considered. According to the simulation results, some segregation channels develop at the corners of the casting. Flow-driven fragments are produced in/around the segregation channels, whereas capillary-driven fragments are produced at a certain depth of the mushy zone across the entire section of the casting. The fragmentation rate caused by the flow-driven mechanism is several orders of magnitude larger than that caused by the capillary-driven mechanism, i.e. the flow-driven fragmentation mechanism is dominant for the currently investigated sample. After the solidification process, four freckles formed at the casting corners on the shadowed side, whereas it was freckle-free on the bright side.

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Section: Discussionmentioning

confidence: 99%

Section: Formation Of Spurious Grains Via Different Fragmentation Mec...mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Numerical study on the formation of spurious grains and freckles during the directional solidification of superalloys

Zhang

Liu

et al. 2023

IOP Conf. Ser.: Mater. Sci. Eng.

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“…Currently, dendrite fragmentation is often observed during X-ray characterizations [21,22]. Possible dendrite-fragmentation mechanisms [23][24][25] include capillary-driven [26][27][28], flowdriven [22,[29][30][31][32], phase-transformation-driven [25,33], and deformation-driven [34][35][36][37] [32] and Liotti et al [29] discovered that the frequency of arm fragmentation is highly dependent on the direction of natural convection through upward and downward directional solidification experiments. Abou-Khalil et al indicated that changes in the dendrite-fragmentation frequency and dendrite-growth rate depend on the gravity level [38].…”

Section: Introductionmentioning

confidence: 99%

High-performance GPU computing of phase-field lattice Boltzmann simulations for dendrite growth with natural convection

Takaki

Sakane

Suzuki

2023

IOP Conf. Ser.: Mater. Sci. Eng.

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The effect of natural convection on dendrite morphology is investigated through three-dimensional large-scale phase-field lattice Boltzmann simulations using a block-structured adaptive mesh refinement scheme with the mother-leaf method in a parallel-GPU environment. The simulations confirmed that downward buoyancy enhances the growth of the primary and secondary arms, and upward buoyancy delays the growth of those arms. In addition, the effect of natural convection on the solidification morphologies gradually decreased as the primary arm tip reached the top of the computational domain and finally stopped. Furthermore, in the longer simulation under purely isothermal diffusive conditions, detachment of the secondary arms owing to curvature-driven fragmentation was observed. A large-scale non-isothermal dendrite growth simulation was also conducted, wherein it was observed that the tip growth rate of the primary arm was delayed, and the secondary arm spacing was larger than that in the isothermal condition.

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Solidification Principle in Large Vertical Steel Casting Under the EMS Effect

Zhang

et al. 2023

Metall Mater Trans B

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The surging demand for large high-quality rotor shafts or similar steel components in heavy industries (energy sector) poses new challenges to steelmakers. Based on the experience of conventional ingot and continuous casting, several new process concepts have been proposed, e.g., vertical continuous casting (VCC), semi-continuous casting (SCC), and segment casting (SC), but none of them are optimally put in operation. The main problems include the control of the as-cast structure and macrosegregation. Electromagnetic stirring (EMS) is necessary to obtain the center equiaxed zone, but EMS-induced multiphase flow can cause severe macrosegregation and uneven distribution of the as-cast structure between equiaxed and columnar. In this study, an advanced mixed columnar-equiaxed solidification model was used to investigate the formation of the as-cast structure and macrosegregation in an example of SCC with a large format (diameter 1 m). The main role of EMS is to create crystal fragments by fragmentation, which is regarded in this work as the only origin of equiaxed grains. The created equiaxed grains are brought by the EMS-induced (primary and secondary) flow and gravity-induced sedimentation to the central/lower part of the casting. The main goal of this study was to understand the solidification principle of SCC. In addition, a numerical parameter study by varying the EMS parameters was also performed to demonstrate the model capability towards the process optimization of SCC.

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Dendrite fragmentation mechanism under forced convection condition by rotating magnetic field during unidirectional solidification of AlSi7 alloy

Cited by 13 publications

References 59 publications

Numerical study on the formation of spurious grains and freckles during the directional solidification of superalloys

Numerical study on the formation of spurious grains and freckles during the directional solidification of superalloys

High-performance GPU computing of phase-field lattice Boltzmann simulations for dendrite growth with natural convection

Solidification Principle in Large Vertical Steel Casting Under the EMS Effect

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