Impact of Crystal Orientation Relationship on Microstructure Evolution in Al-Ag-Cu Ternary Eutectic

The invariant ternary eutectic of the Al-Ag-Cu system can solidify with a variety of microstructural patterns for which differences in processing conditions are only partially responsible. Particularly, the occurrence of non -chain-like patterns has not yet been fully analyzed and described, especially regarding the role of crystallo-graphic orientations. To evaluate the impact of the crystallographic orientations on the microstructural pattern formation within directionally solidified Al-Ag2Al-Al2Cu, a survey of previous work on orientation relationships in this and other three-phase eutectics was conducted, then a systematic experimental study carried out on multiple eutectic grains within a single sample at different solidification distances using scanning electron mi-croscopy and electron backscatter diffraction. Eutectic grains with chain-like and non-chain-like patterns were analyzed and the orientation relationships between the three phases were determined. Building off earlier work, the relation between highly ordered chain-like patterns and their orientation relationships is further elucidated and an overall correlation of less-ordered non-chain-like patterns with their orientation relationship is estab-lished. Thus, a mechanism for non-chain-like pattern evolution at nucleation and during growth regarding the present orientations is proposed, which can serve as a basis for controlled microstructure adjustments.