Impact of crystal orientation relationship on microstructure evolution in Al-Ag-Cu ternary eutectic

Abstract

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 crystallographic 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 microscopy 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 established. 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.