Shape casting of Al2O3-YAG ceramics by using Undercooled melt

Al_2O_3-Y_2O_3系统富Al_2O_3部分存在两个共晶系统：一个是Al_2O_3-YAG平衡共晶系统，另一个是Al_2O_3-YAP亚稳态共晶系统。将Al_2O_3-YAP亚稳共晶组织加热到亚稳共晶温度以上，但低于平衡共晶温度，产生过冷熔体。平衡路径上的凝固紧跟在过冷熔体形成之后。随着亚稳共晶组织的熔化，在平衡路径上的凝固形成了细小均匀的平衡共晶组织，片层间距小于1μm，过冷熔体形成所用的亚稳共晶组织不影响平衡共晶组织。利用Al_2O_3-YAP亚稳共晶组织熔化产生的过冷熔体，实现了氧化铝棒材的异形铸造和连接。整个铸件都获得了细小的共晶组织。与传统的过冷熔体凝固相比，凝固与熔化耦合获得了更高的生长速率。动力学效应导致的偏斜耦合生长区有助于在亚稳共晶成分处形成细小的共晶组织。

There are two eutectic systems in the Al_2O_3-rich portion of the AI_2O_3-Y_2O_3 system: one is the A1_2O_3-YAG equilibrium eutectic system and the other is the A1_2O_3-YAP metastable eutectic system. Heating the A1_2O_3-YAP metastable eutectic structure up to temperatures above the metastable eutectic temperature but below the equilibrium eutectic temperature produced the undercooled melt. Solidification in the equilibrium path immediately followed the undercooled melt formation. The solidification in the equilibrium path along with the melting of the metastable eutectic structure resulted in a fine and uniform equilibrium eutectic structure with lamellar spacing of less than 1 μm. The equilibrium eutectic structure was not affected by the metastable eutectic structure used for the undercooled melt formation. Shape casting and joining of alumina rods were demonstrated using the undercooled melt produced by the melting of is the A1_2O_3-YAP metastable eutectic structure. The fine eutectic structure was obtained throughout the castings. Coupling of the solidification and the melting achieved a higher growth rate than conventional solidification from the undercooled melt. The skewed coupled growth zone due to the kinetic effect contributed to formation of the fine eutectic structure at the metastable eutectic composition.