Abstract
A numerical study on columnar-to-equiaxed transition (CET) during directional solidification of binary alloys is presented using a macroscopic solidification model. The position of CET is predicted numerically using a critical cooling rate criterion reported in literature. The macroscopic solidification model takes into account movement of solid phase due to buoyancy, and drag effect on the moving solid phase because of fluid motion. The model is applied to simulate the solidification process for binary alloys (Sn–Pb) and to estimate solidification parameters such as position of the liquidus, velocity of the liquidus isotherm, temperature gradient ahead of the liquidus, and cooling rate at the liquidus. Solidification phenomena under two cooling configurations are studied: one without melt convection and the other involving thermosolutal convection. The numerically predicted positions of CET compare well with those of experiments reported in literature. Melt convection results in higher cooling rate, higher liquidus isotherm velocities, and stimulation of occurrence of CET in comparison to the nonconvecting case. The movement of solid phase aids further the process of CET. With a fixed solid phase, the occurrence of CET based on the same critical cooling rate is delayed and it occurs at a greater distance from the chill.
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Abbreviations
- c p :
-
Specific heat (J/kg-K)
- C :
-
Species concentration (kg/kg)
- f :
-
Mass fraction
- D :
-
Mass diffusion coefficient of the species (m2/s)
- g :
-
Acceleration due to gravity (m/s2)
- g l :
-
Volume fraction of liquid
- g s :
-
Volume fraction of solid
- G L :
-
Temperature gradient (K/m)
- ΔH :
-
Latent enthalpy content of a control volume (J/kg)
- k p :
-
Partition coefficient
- L :
-
Latent heat of fusion (J/kg)
- p :
-
Pressure (N/m2)
- r :
-
Cooling rate (K/s)
- S :
-
Source term
- t :
-
Time (s)
- T :
-
Temperature (K)
- u :
-
Continuum velocity vector (m/s)
- V L :
-
Tip velocity (m/s)
- x, y :
-
Coordinates
- β T :
-
Thermal expansion coefficient (1/K)
- β C :
-
Solutal expansion coefficient
- μ :
-
Dynamic viscosity (kg/s-m)
- ρ :
-
Mixture density (kg/m3)
- cr:
-
Critical
- eff:
-
Effective
- i:
-
Initial
- l:
-
Liquid phase
- mix:
-
Mixture
- ref:
-
Reference
- s:
-
Solid phase
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The authors gratefully acknowledge the financial support of General Motors Corporation, USA.
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Kumar, A., Dutta, P. Numerical studies on columnar-to-equiaxed transition in directional solidification of binary alloys. J Mater Sci 44, 3952–3961 (2009). https://doi.org/10.1007/s10853-009-3539-z
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DOI: https://doi.org/10.1007/s10853-009-3539-z