Dynamics of spacing selection of a lamellar eutectic during directional solidification

The coupling equation of the lamellar eutectic Al-Al2Cu during directional solidification is solved numerically. The profile of the solidifying interface, the supercooling at the three-phase conjunction point (TPCP) and the tilting angle of the α-β phase boundary have been investigated as functions of the lamellar spacing. The dynamics of local spacing selection (formation of a termination) is determined by the tilting of the α-β boundary and the splitting features of the solidifying interface. Correspondingly, there are four dynamic modes of local spacing selection. Calculations show that the tilting angle equals zero when the supercooling at the TPCP reaches its minimum value min (ΔT0) and the α-liquid and β-liquid interfaces are in the critical splitting state as a function of the spacing. The analysis provides a solid physical basis for the conjecture that the operating point of spacing selection corresponds to the minimum point min (ΔT0).