Thermosolutal convection during directional solidification. II. Flow transitions

The mold geometry and its thermal properties greatly influence the solidification process. Finite element simulations of directional solidification in various molds are presented. These simulations were performed using volume averaged properties in the mushy zone in order to model the convection, transport of solute and energy, and phase change occurring during solidification. These simulations show the interactions of the mold and alloy with the resultant solidification phenomena, including steepling. Mold geometries can cause macrosegregation because of shrinkage flows, by interrupting the development of the mushy zone, and by causing or influencing thermosolutal convection. Mold materials with different thermal properties result in different macrosegregation patterns even for the same geometries. Changes in cross section and the thermal properties of the mold also affect the gradients and solidification rates obtained in the alloy, as opposed to those measured on the mold wall. Simulations are compared qualitatively to a verification experiment of directionally solidifying a hypoeutectic Al-7wt%Si alloy in a mold with changing cross sections.

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Thermosolutal convection and macrosegregation during directional solidification of TiAl alloys in centrifugal casting

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2020.119698 ◽

2020 ◽

Vol 154 ◽

pp. 119698 ◽

Cited By ~ 1

Author(s):

Martín Cisternas Fernández ◽

Miha Založnik ◽

Hervé Combeau ◽

Ulrike Hecht

Keyword(s):

Directional Solidification ◽

Centrifugal Casting ◽

Thermosolutal Convection ◽

Tial Alloys

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Traveling Waves Induced by Sweeping Flows on Solidification Interfaces

Materials Science Forum ◽

10.4028/www.scientific.net/msf.941.1546 ◽

2018 ◽

Vol 941 ◽

pp. 1546-1551

Author(s):

Alain Pocheau ◽

Tania Jiang ◽

Marc Georgelin

Keyword(s):

Directional Solidification ◽

Traveling Waves ◽

Thermal Gradient ◽

Large Scale ◽

Solid Phase ◽

Travelling Waves ◽

Thermosolutal Convection ◽

Solidification Interface

Solidification of alloys in a thermal gradient usually involves the generation of flows by thermal or thermosolutal convection. We experimentally study their effects on the dynamics of a solidification interface by inducing a controlled sweeping flow in a directional solidification device. Flow is induced in the sample from an external thermosiphon. Downstream inclination of microstructures and downstream sidebranch development are observed. However, the major outcome is the evidence of large scale travelling waves on the solidification interface. They are induced by the coupling between solidification and flow and yield repetitive striations of the solid phase. Two waves are observed and characterized.

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Spurious Grain Formation at Cross-Sectional Expansion During Directional Solidification: Influence of Thermosolutal Convection

Journal of Materials Engineering and Performance ◽

10.1007/s11665-018-3364-0 ◽

2018 ◽

Vol 27 (6) ◽

pp. 3122-3130

Author(s):

M. Ghods ◽

M. Lauer ◽

S. R. Upadhyay ◽

R. N. Grugel ◽

S. N. Tewari ◽

...

Keyword(s):

Directional Solidification ◽

Thermosolutal Convection ◽

Cross Sectional ◽

Grain Formation

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Effect of thermosolutal convection on directional solidification

Sadhana ◽

10.1007/bf02728482 ◽

2001 ◽

Vol 26 (1-2) ◽

pp. 121-138 ◽

Cited By ~ 4

Author(s):

Suresh V. Garimella ◽

James E. Simpson

Keyword(s):

Directional Solidification ◽

Thermosolutal Convection

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Application of the Meshless Element-Free Galerkin Method to Freckle Formation in Directional Solidification

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-11257 ◽

2009 ◽

Cited By ~ 1

Author(s):

Udaya K. Sajja ◽

Sergio D. Felicelli

Keyword(s):

Finite Element ◽

Directional Solidification ◽

Turbine Blades ◽

Solidification Process ◽

Solute Concentration ◽

Momentum Equation ◽

Thermosolutal Convection ◽

Element Free Galerkin ◽

Solidification Processes ◽

Element Free

Freckles or channel segregates are the most severe form of the macrosegregation that can occur in unidirectionally solidified superalloy castings used in the manufacturing of gas turbine blades. These defects are formed due to thermosolutal convection during solidification. Mathematical modeling of the solidification process involves the simultaneous solution of the conservation equations of momentum, energy and solute concentration in all regions (liquid, mush and solid). Most numerical simulations of dendritic solidification processes have been performed using finite element or the finite volume techniques. The dependence of these methods on the mesh is not always advantageous for problems in which discontinuities or regions of sharp gradients do not coincide with the original mesh lines. In the present work, the meshless element free Galerkin (EFG) method has been investigated to simulate directional solidification processes in which sharp gradients in the field variables can occur as a result of the formation of channels. Simulations of a multicomponent Ni-Al-Ta-W alloy have been performed in a two dimensional domain. The calculations are started with the alloy in all-liquid state and the growth of the mushy zone is followed in time. A projection method is used to solve the momentum equation which makes the computation more efficient than the previously used penalty method. The accuracy of the EFG results is compared with that of the finite element calculations and the potential advantages of the meshless methods for this type of problems are discussed.

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