Microstructure of the directionally solidified ternary eutectic ceramic Al2O3/MgAl2O4/ZrO2

The directionally solidified Al2O3/MgAl2O4/ZrO2 ternary eutectic ceramic was prepared via induction heating zone melting. Smooth Al2O3/MgAl2O4/ZrO2 eutectic ceramic rods with diameters of 10 mm were successfully obtained. The results demonstrate that the eutectic rods consist of Al2O3, MgAl2O4 and ZrO2 phases. In the eutectic microstructure, the MgAl2O4 and Al2O3 phases form the matrix, the ZrO2 phase with a fibre or shuttle shape is embedded in the matrix, and a quasi-regular eutectic microstructure formed, presenting a typical in situ composite pattern. During the eutectic growth, the ZrO2 phase grew on non-faceted phases ahead of the matrix growing on the faceted phase. The hardness and fracture toughness of the eutectic ceramics reached 12 GPa and 6.1 MPa·m 1/2, respectively, i.e., two times and 1.7 times the values of the pre-sintered ceramic, respectively. In addition, the ZrO2 phase in the matrix reinforced the matrix, acting as crystal whiskers to reinforce the sintered ceramic.