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 un dercoolings by a SiO2 trigger needle. The apparent plateau after recalescen ce disappeared at around DeltaT = 500 K and the post-recalescence temperatu re (T-post) decreased from the melting point with further increase in under cooling, DeltaT(hyp) of YAG was estimated to be 769 K using the specific he at of liquid that was evaluated by a heat-transfer calculation from the obt ained cooling curves. T-post decreased before reaching the estimated DeltaT (hyp). Although this behavior was ascribed to heat extraction by the levita tion gas, which suggests that the YAG melt did not solidify adiabatically d ue to the low thermal conductivity, the maximum undercooling of 1060 K indi cates that the YAG melt solidified beyond DeltaT(hyp). Moreover, the cellul ar morphology of YAG was observed even beyond DeltaT(hyp). It can be seen t hat the cellular morphology is retained since the thermal supersaturation d oes not reach unity at DeltaT(hyp) due to the large kinetic effect. (C) 200 1 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserv ed.