Dresden 2003 – scientific programme

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M: Metallphysik

M 6: Symposium: Phasenumwandlungen in Schmelzen IV

M 6.2: Talk

Monday, March 24, 2003, 16:45–17:00, IFW A

Phase Field Simulations of Lamellar Growth for Ternary Eutectic Alloys — •Markus Apel, Bernd Böttger, Victor Vitusevych, and Ingo Steinbach — Access e.V., Intzestr.5, 52072 Aachen

At the invariant point ternary eutectic alloys solidify as three phases. The phase fractions are determined by thermodynamics. For the calculation of growth structures diffusion and surface tension has to be taken into account. This is done by phase field models. In this contribution solid-liquid interfacial undercooling for two–dimensional lamellar growth modes were investigated. The undercooling is important for the selection of growth structures. The applied phase field model is coupled to a thermodynamic database for calculation of phase equilibria. This enables the treatment of real alloys. Surface tension is considered to be constant, diffusion is calculated only with diagonal terms. Calculations for AlAgCu show coupled lamellar growth, whereas different stacking sequences of the three solid phases have different interfacial undercooling. Compared to the fixed AB stacking sequence of a binary eutectic a new non–axisymmetric growth mode appears. The simplest ABC stacking sequence violates mirror symmetry around the growth direction and therefore eutectic lamellae can grow inclined to the thermal gradient even for small undercooling. The selected growth structure depends furthermore on equilibrium phase fractions. This is shown for AgCuZn, which has only 2% fcc-Cu phase and the structure consists mainly of a simple AB sequence.