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Working Group
Ursula
Kattner
Bill Boettinger
Dilip Banerjee
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Lever rule solidification and Scheil
solidification are illustrated for the case of a Ni-.09Al-.08Ta alloy.
The thermodynamic description of Ni-Al-Ta from the 1995 thesis of N.
Dupin (nathdupin.free.fr/public/Download/these.pdf) was used for the
present calculations.
The liquid concentration paths are shown together with the liquidus
projection of the Ni-rich part of the Ni-Al-Ta system. The gamma phase
(Ni) is the primary phase for both solidification paths. Under Scheil conditions the
alloy encounters the L -> gamma + gamma' monovariant eutectic where
both phases form simultaneously from the liquid phase. The path
encounters then the four phase reaction, L + gamma' -> gamma + pi.
Under Scheil assumptions fraction and concentration profile of the
gamma' phase become fixed and solidification continues along the
monovariant eutectic, L -> gamma + pi, until solidification is completed with
the ternary eutectic reaction, L -> gamma + pi + Ni3Ta.
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| The sequence
of phase formation during lever rule solidification can also be
obtained from an isopleth that includes the alloy composition.
However, since the tie-lines usually do not lie within the plane of the
isopleth, no information about phase amounts, phase composition or the
Scheil solidification can be obtained. |
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The differences between a lever rule and Scheil solidification paths can
be seen in plots of the phase fractions and enthalpies. Since under
Scheil assumptions the concentration of the solid phases is "frozen"
after solidification is complete, only the temperature dependence of
the enthalpies is recorded after completion of solidification.
Lever rule solidification
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Scheil solidification
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