Three-dimensional observation of the entangled eutectic structure in the Al2O3-YAG system

The coupled growth zone of the Al2O3-YAG eutectic system was examined by means of high resolution X-ray tomography. The entangled eutectic structure was observed for the unidirectional solidification and the solidification from the undercooled melt at the equilibrium eutectic composition (Al2O3-18.5 mol% Y2O3). The reconstructed three-dimensional images showed that both the Al2O3 and the YAG phases branched and that the entangled domain was of the same order as the lamellar spacing. Comparison of the branching in the Al2O3-YAG eutectic system to that in metallic alloys that exhibit the regular or the irregular eutectic structure indicated that the frequent branching of both phases resulted in the entangled structure.