Abstract
A mathematical model was developed to calculate microsegregation in binary metallic alloys. This model utilized the mathematical techniques of the method of lines combined with invariant imbedding (MOL/II) to solve the problem of combined heat and mass transfer during and after solidification. Model predictions were compared to experimental measurements in the Al-Cu system and to other microsegregation models. The MOL/II model predicted nonequilibrium second-phase contents within ±3 pct at low and intermediate cooling rates, when dendrite-arm coarsening was included in the model. It also was able to reproduce concentration profiles reasonably well. The analytical models commonly used (equilibrium cooling, Scheil equation, Brody/ Flemings model, Clyne/Kurz model, Solari/Biloni model, and Basaran equation) in micro-segregation calculations were shown to be considerably less accurate than the numerical models (MOL/II and the Ogilvy/Kirkwood model).
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Abbreviations
- A :
-
constant used in coarsening equations
- C e :
-
solute concentration in liquid at eutectic temperature (mole pct)
- Cg227p:
-
heat capacity (J/kg K) Co initial solute concentration (mole pct)
- C :
-
concentration of solute (mole pct)
- D :
-
chemical diffusivity of solute (m2/s)
- ΔH f :
-
enthalpy of fusion (J/kg)
- h :
-
location of interface (m)
- k :
-
equilibrium partition coefficient (mole pct solute in solid/mole pct solute in liquid)
- m :
-
slope of liquidus curve (K/mole pct)
- n :
-
exponent from Eq. [1]
- q :
-
mass flux, defined by Eq. [13] (mole pct × m/s)
- R :
-
Riccati parameter, defined by Eq. [18] (m2 K/W)
- S :
-
Riccati parameter, defined by Eq. [19] (m/s)
- T :
-
temperature (K) 70 melting point of pure solvent (K)
- T ∗ :
-
temperature at interface (K)
- t :
-
time (s)
- t s :
-
solidification time (s) v heat flux, defined by Eq. [12] (W/m2)
- w :
-
Riccati parameter, defined by Eq. [18] (K)
- x :
-
position (m)
- z :
-
Riccati parameter, defined by Eq. [19] (mole pct x m/s) α
- ρCpΔt:
-
(W/m3 K)
- β :
-
pre-exponential term in Eq. [1] (m)
- Γ:
-
Gibbs-Thomson coefficient (K m)
- ε:
-
cooling rate (K/s)
- κ:
-
thermal conductivity (W/m K)
- λ :
-
dendrite-arm spacing (m)
- λ 0 :
-
initial secondary dendrite-arm spacing (m)
- λ 1 :
-
primary dendrite-arm spacing (m)
- λ 2 :
-
secondary dendrite-arm spacing (m)
- ρ:
-
mass density (kg/m3)
- Σ:
-
parameter used in determination of interface position (mole pct × m/s) Subscripts/Superscripts
- S :
-
solid
- L :
-
liquid
- n :
-
current time-step
- i :
-
current mesh point int at interface
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Formerly Graduate Research Assistant, The University of Michigan
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Battle, T.P., Pehlke, R.D. Mathematical modeling of microsegregation in binary metallic alloys. Metall Trans B 21, 357–375 (1990). https://doi.org/10.1007/BF02664204
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DOI: https://doi.org/10.1007/BF02664204