Microstructure and Mechanical Properties of Al₂O₃/Er₃Al₅O₁₂ Binary Eutectic Ceramic Prepared by Bridgman Method

Directionally solidified Al₂O₃/Er₃Al₅O₁₂ (EAG) eutectic ceramic was prepared via vertical Bridgman method with high-frequency induction heating. The effects of the growth rate on the microstructure and mechanical properties of the solidified ceramic were investigated. The experimental results showed that there were no pores or amorphous phases in the directionally solidified Al₂O₃/EAG eutectic ceramic. Al₂O₃ phase was embedded in the EAG matrix phase, and the two phases were intertwined with each other to form a typical binary eutectic "hieroglyphic" structure. With the increase of growth rate, the phase size and spacing of the solidified Al₂O₃/EAG ceramic both decreased, and the growth rate and phase spacing satisfied the λ²v ≈ 60 formula of Jackson-Hunt theory. The cross section microstructure of the solidified ceramic always exhibited an irregular eutectic growth, while the longitudinal section microstructure presented a directional growth. The mechanical properties of the solidified ceramic gradually increased with the increase of growth rate, and the maximum hardness and fracture toughness could reach 21.57 GPa and 2.98 MPa·m^1/2 respectively. It was considered that the crack deflection and branching could enhance the toughness of the solidified ceramic effectively.