Preparation of directionally solidified Al2O3/YAG/ZrO2 ternary eutectic ceramic with induction heating zone melting

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Al2O3/YAG/ZrO2 directionally solidified eutectic ceramics (DSECs) were prepared via induction heating zone melting (IHZM), in which sintered ceramic rods were used as the preform. The DSECs consisted of Al2O3, Y3Al5O12 (YAG), and ZrO2 phases, similar to the sintered preforms. The microstructure of the DSECs was similar to a “sponge-net” structure, wherein the three phases exhibited coupled growth; the YAG phase made up the matrix, and the Al2O3 and ZrO2 phases formed the framework of the sponge-net. The eutectic inter-phase spacing (λ) gradually decreased with an increase in the growth rate (v), and this was in accordance with a constant λ2v of about 100. The difference in the microstructures of the DSECs prepared via IHZM and a natural-cooling solidified eutectic ceramic (NCSEC) was attributed to the different nucleation and growth modes. The hardness and fracture toughness of the DSECs were 16.1 GPa and 2.98 MPa m1/2, respectively, which were 1.82 and 1.27 times those of a sintered ceramic. The ZrO2 phase exhibited a toughening effect in a variety of ways such as crack bridging, crack deflection, crack branching, and crack pinning. The hardness and fracture toughness showed complex variations due to the size effect of the ZrO2 phase and defect reduction. The ZrO2 phase distribution effect improved the fracture toughness of the NCSEC and the DSECs prepared at high growth rates.