PHASE-FIELD SIMULATIONS OF DENDRITIC/GLOBULAR AND EUTECTIC SOLIDIFICATION IN NI-CU-CR AND AL-CU ALLOYS

摘要

Phase transformations in multicomponent and multiphase systems play a major role during solidification processes of a variety of alloys. Using a recently developed phase-field model for multicomponent and multiphase systems, we apply our adaptive finite element simulation code to numerically investigate dendritic/globular and eutectic phase transitions in Ni- and Al- alloys. For a ternary Ni-Cu-Cr alloy, we perform a series of numerical computations with varying alloy compositions and at a fixed undercooling. For increasing amount of Cr, a morphological transition from dendritic to globular growth can be observed. The dependence of the growth velocity and of the impurity segregation in the solid phase on the composition is analyzed and indicates a smooth type of transition between the dendritic and the globular structures. The stability of eutectic structures in binary Al-Cu alloys is investigated. The growth morphology strongly depends on the composition of the melt and on the volume fractions of the solidifying solids. We examine the growth dynamics, the characteristic eutectic spacings, the volume fractions of the two solid phases and the type of morphology: Regular lamellae and oscillatory patterns for different off-eutectic compositions.