Crystal orientation and morphology in Al-Ag-Cu ternary eutectic

Abstract

Ternary eutectics provide a unique opportunity for studying the e�ects of complex microstructure formation, as three distinct phases must be formed simultaneously from the melt. In order to produce fully coupled three-phase growth, Al-Ag-Cu at the ternary eutectic composition was directionally solidi�ed in a constant temperature gradient of 3 K/mm at velocities between 0.2 and 5.0 �m/sec. Under these conditions, the two intermetallic phases appear to grow as closely coupled rods in an �(Al) matrix, with the solidi�cation velocity a�ecting the speci�c morphologies chosen by the rods and the general degree of alignment of the structure. Crystal orientations were examined by EBSD to determine if variations in morphology within a single sample are due to speci�c orientation relationships. Although no conclusive connection to morphology has yet been found, two di�erent sets of orientation relationships between the three phases have thus far been identi�ed.