Morphological Characterization of Eutectic Si and Ge Phases in the Corresponding Al-15Si and Al-20Ge Alloys Using FIB Tomography

The three-dimensional morphology of the eutectic ge phase in samples modified by ca and y in the hypoeutectic al-20ge alloy has been investigated by focused ion beam tomography. addition of ca (0.2 wt.%) caused a modification of the eutectic ge phase from a branched plate-like morphology to a compressed cylinder-like shape of smaller dimensions. addition of y (0.2 wt.%) resulted in a transformation of the eutectic ge phase with two types of morphology. one type is vermicular-like in 2d and refined plate-like in 3d, while the other appears as a holey ge matrix with an embedded eutectic al phase of rod-like morphology. the morphology of the modified eutectic ge has been discussed in terms of possible growth mechanisms compared with that of the as-cast non-modified al- 20ge alloy and that of well-known sr-modified eutectic si in al-si system.