TY - JOUR

T1 - Validation of a capillary-driven fragmentation model during mixed columnar-equiaxed solidification with melt convection and grain transport

AU - Rodrigues, Christian M.G.

AU - Wu, Menghuai

AU - Zhang, Haijie

AU - Ludwig, Andreas

AU - Kharicha, Abdellah

N1 - Publisher Copyright: © 2022

PY - 2022/6

Y1 - 2022/6

N2 - 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.

AB - 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.

KW - Alloy solidification

KW - Fragmentation

KW - Microstructural transition

KW - Model validation

KW - Remelting

KW - Volume-average model

UR - http://www.scopus.com/inward/record.url?scp=85132438164&partnerID=8YFLogxK

U2 - 10.1016/j.mtla.2022.101462

DO - 10.1016/j.mtla.2022.101462

M3 - Article

AN - SCOPUS:85132438164

VL - 23.2022

JO - Materialia

JF - Materialia

SN - 2589-1529

IS - June

M1 - 101462

ER -