Influence of the Phase Fractions on the Formation of Eutectic Colonies: A Large‐Scale Phase‐Field Study

The growth of two-phase eutectic colonies is a frequently observed phenomenon in the microstructure of directionally solidified ternary alloys. The formation of these macroscopic structures is driven by microscopic instabilities, caused by
minor component impurities, diffusing into the liquid from the two solidifying phases. Due to an accumulation of this impurity component, a morphological instability at the eutectic front leads to the formation of eutectic colonies. In this
work, the phase-field method is used to investigate the influence of different melt composition and hence of the adjusting phase fractions on the growth of eutectic colonies. For this purpose, specially designed model systems, N-xA-yC, with defined phase fractions of the solids are generated on the basis of the high performance material NiAl-34Cr. Based on these models, the evolution of eutectic colonies is investigated in two- and three-dimensional (3D) large-scale
simulations with up to 3⋅10 9 cells. To perform these highly computationally intense large-scale 3D simulations, the computational framework used is optimized in several layers. The results obtained show the influence of the
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melt composition on the formation and characteristics of the evolved eutectic colonies and provide new insights into the formation of these macroscopic structures.