Validation of a capillary-driven fragmentation model during mixed columnar-equiaxed solidification with melt convection and grain transport
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- Christian-Doppler Lab for Metallurgical Applications of Magnetohydrodynamics
Abstract
A mixed columnar-equiaxed solidification model was recently extended to capture the capillary-driven fragmentation phenomenon, which was considered the only mechanism for the formation of equiaxed crystals. The purpose of the present study was to validate the model by replicating a laboratory experiment on the solidification of an aqueous ammonium chloride solution (Gao and Wang, 1999). The experiment was performed by cooling the solution in a vertical test cell from the top surface to allow columnar dendrites to grow. Owing to the fragmentation of the downward-growing columnar dendrites, equiaxed fragments appeared, sedimented, and created a bed of crystals at the bottom of the cell. This pile-up of crystals ultimately met the columnar-tip front coming from the top, thereby leading to a structural transition (columnar-to-equiaxed transition). This experiment was successfully reproduced numerically for the first time, which involved coupling between the following phenomena: fragmentation, melt convection, grain transport, a pile-up of equiaxed crystals, and the potential growth of columnar dendrites from a bed of equiaxed crystals (equiaxed-to-columnar transition). A satisfactory agreement was achieved between the simulation and experimental results. Knowledge about capillary-driven fragmentation was strengthened by analyzing the microstructural evolution. Alloy-dependent parameters Ss0, K0, and a that govern dendrite coarsening and fragmentation were proposed for an aqueous ammonium chloride solution. Finally, the limitations of the current version of the fragmentation model were discussed.
Details
Original language | English |
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Article number | 101462 |
Number of pages | 12 |
Journal | Materialia |
Volume | 23.2022 |
Issue number | June |
Early online date | 26 May 2022 |
DOIs | |
Publication status | Published - Jun 2022 |