Microstructure and fracture toughness of directionally solidified Al₂O₃/YAG/ZrO₂ eutectic ceramics by laser zone remelting

Directionally solidified Al₂O₃/YAG/ZrO₂ eutectic ceramics were prepared by laser zone remelting technique to investigate the rapid solidification microstructure characteristic under ultra-high temperature gradient and different laser processing conditions. The fracture toughness and toughen mechanism were analyzed and discussed. The results show the following. (1) The directionally solidified Al₂O₃/YAG/ZrO₂ eutectic ceramic shows a ‘Chinese script’ microstructure consisting of only three phases of Al₂O₃, YAG and ZrO₂, and no other phases and colonies. The three phases distribute homogeneously and continuously, connect and finely couple each other to form an interpenetrating network, which belongs to the typical lamellar structure of a rapidly solidified irregular eutectic. (2) The eutectic spacing decreases with the increase of scanning rate under certain laser power intensity, and the smallest spacing is only about 0.2~0.3 μm. (3) Some amount of Y₂O₃ dissolves in ZrO₂ phase and this influences the micro-patterns of ZrO₂. (4) The maximum hardness reaches 18.67 GPa and the room-temperature fracture toughness is 8.O MPa·m^1/2. Adding the third component of ZrO₂, small size of phases and crack branching may contribute to the increased fracture toughness.