Crystal orientation relationships in ternary eutectic Al-Al2Cu-Ag2Al

The microstructure of ternary eutectic Al-Al2Cu-Ag2Al arranges in several patterns of three solid phases during directional solidification. One key question for understanding the behavior of this system is if and how the patterns depend on crystal orientation relationships (ORs) between the solid phases. In order to study the correlation between the ORs and the evolving patterns for different process conditions, electron backscatter diffraction (EBSD) is performed on samples of directionally solidified ternary eutectic Al-Al2Cu-Ag2Al which have been processed with different solidification velocities and temperature gradients. The results show that characteristic ORs occur, influencing the type of the evolving pattern, the alignment of the phases and the degree of order. For one specific OR the pattern was observed to change in response to an imposed increase in the growth velocity even though the OR was retained. Based on the obtained EBSD results, an explanation for the observed behavior is proposed. For the other ORs, specific microstructures were observed for each of them. The outcomes demonstrate that knowledge about crystal ORs is essential to improve the understanding of the pattern formation in complex eutectic alloys. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.