Production of undercooled melt by heating the metastable Al2O3-YAP eutectic structure

This paper demonstrates the undercooled melt formation from the metastable eutectic structure by heating procedures in the Al2O3-YAG system. Phase tra nsformation during heating/cooling procedures is detected by optical DTA eq uipment. Firstly, the Al2O3-YAP metastable eutectic structure is obtained b y solidification after heating the melt above 2273 K. The undercooled melt formation is confirmed when the Al2O3-YAP metastable eutectic structure com posed of crystalline phases is heated up to temperatures above the metastab le eutectic temperature for the equilibrium eutectic composition (18.5 mol% Y2O3) and the metastable eutectic composition (23.5 mol%Y2O3). The undercoo led melt formation is immediately followed by the solidification in the Al2 O3-YAG equilibrium path for the 18.5 mol%Y2O3 specimens. For the 23.5 mol%Y 2O3 specimens, the obtained undercooled melt is kept even for as long as 36 00 s without solidification. Furthermore, the fine and uniform Al2O3-YAG eu tectic structure is obtained when the melting and the solidification simult aneously occur. The solidification with the exothermic heat beside the melt ing with the endothermic heat has a great advantage for heat release of the latent heat. Consequently, the high growth rate leads to the fine eutectic structure in the off-eutectic composition.