Modeling fluid flow in three-dimensional single crystal dendritic structures

• Published in: Acta materialia Vol. 58; no. 8; pp. 2864 - 2875
• Main Authors: Madison, J., Spowart, J., Rowenhorst, D., Aagesen, L.K., Thornton, K., Pollock, T.M.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-05-2010; Elsevier
• Subjects: Applied sciences; Dendritic growth; Directional solidification; Exact sciences and technology; Metals. Metallurgy; Modeling; Nickel alloys; Permeability; Dendritic growth; Nickel alloys; Permeability; Directional solidification; Modeling; Flow(fluid); Magnetic permeability; Microstructure; Single crystal; Dendritic structure; Dendrite; Crystalline structure
• DOI: 10.1016/j.actamat.2010.01.014
• EISSN: 1873-2453
• ISSN: 1359-6454

Convection during directional solidification can cause defects such as freckles and misoriented grains. To gain a better understanding of conditions associated with the onset of convective instabilities, flow was investigated using three-dimensional (3D) computational fluid dynamics simulations in an experimentally obtained dendritic network. A serial-sectioned, 3D data set of directionally solidified nickel-base superalloy measuring 2.3
×
2.3
×
1.5
mm was used to determine the permeability for flow parallel and normal to the solidification direction as a function of solid fraction (
f
S
). Anisotropy of permeability varies significantly from 0.4
<
f
S
<
0.6. High flow velocity channels exhibit spacings commensurate with primary dendrite arms at the base of the mushy zone but rapidly increase by a factor of three to four towards dendrite tips. Permeability is strongly dependent on interfacial surface area, which reaches a maximum at
f
S
=
0.65. Results from the 3D simulation are also compared with empirical permeability models, and the microstructural origins of departures from these models are discussed.