Rapid solidification of Y3Al5O12 garnet from hypercooled melt

Containerless solidification of Y3Al5O12 garnet (YAG) was carried out using an aero-acoustic levitator to elucidate the solidification process beyond the hypercooling limit (DeltaT(hyp)). A YAG melt was seeded at different undercoolings by a SiO2 trigger needle. The apparent plateau after recalescence disappeared at around DeltaT = 500 K and the post-recalescence temperature (T-post) decreased from the melting point with further increase in undercooling, DeltaT(hyp) of YAG was estimated to be 769 K using the specific heat of liquid that was evaluated by a heat-transfer calculation from the obtained cooling curves. T-post decreased before reaching the estimated DeltaT(hyp). Although this behavior was ascribed to heat extraction by the levitation gas, which suggests that the YAG melt did not solidify adiabatically due to the low thermal conductivity, the maximum undercooling of 1060 K indicates that the YAG melt solidified beyond DeltaT(hyp). Moreover, the cellular morphology of YAG was observed even beyond DeltaT(hyp). It can be seen that the cellular morphology is retained since the thermal supersaturation does not reach unity at DeltaT(hyp) due to the large kinetic effect. (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.