Study of pattern selection in 3D phase-field simulations during the directional solidification of ternary eutectic Al-Ag-Cu

During the directional solidification of ternary eutectic alloys, different arrangements of the three solid phases evolve, leading to multiple microstructure patterns. These patterns influence the macroscopic properties of the alloy. Different arrangements are even found in single micrographs for the same imposed process conditions. Gaining a better understanding of the complex mechanisms leading to these different patterns is crucial to obtain tailored microstructures with specific properties. To exploit the different patterns which appear in ternary eutectic Al-Ag-Cu, a coupled approach is undertaken using a large-scale simulation and extensive parameter studies on smaller 3D domains. Three patterns found in both large-scale simulations as well as experimental micrographs are investigated with smaller domain size simulations by systematically varying the lamellar spacings. The resulting undercooling-spacing correlations of all investigated phase arrangements follow a Jackson-Hunt-type shape. Different stability ranges of the initially set microstructure are found, and depending on the lamellar spacings, the pattern with the lowest undercooling changes. The combination of both outcomes gives an explanation for the presence of different patterns within single micrographs of directionally solidified ternary eutectic alloys. (C) 2018 Elsevier B.V. All rights reserved.