Microstructural stability and high temperature strength of directionally solidified Al2O3/Er3Al5O12/ZrO2 eutectic ceramics

Al2O3/Er3Al5O12(EAG)/ZrO2 directionally solidified eutectic ceramics (DSECs) were prepared with high frequency induction heating zone melting (IHZM), and heat treated at high temperature. Their phase components, microstructures, flexural and tensile strengths were investigated. The results indicated that the microstructures were composed of the mutually interpenetrated Al2O3, EAG and ZrO2 (stabilized by Er3+ ion) phases. As the growth rate increased from 2 mm/h to 20 mm/h, the phase size decreased and the irregular microstructure became regular. When the heat treatment temperature was up to 1400 °C, the ionic diffusion was triggered and the phase began to grow. Under the action of surface energy and special microstructure, the growth of phase stopped after it reached a certain threshold. The sample with smaller phase size exhibited higher strength at room temperature, which was dependent on the crack propagation resistance. However, the speed of strength reduction was faster. The formation of surface groove, microcrack and malignant growth phase was responsible for this rapidly decreasing of strength. The flexural and tensile strengths of eutectic ceramic with larger phase size remained at 671.6 MPa and 359.45 MPa after long-term heat treatment at 1500 °C, respectively. The smaller difference between the original phase size and the maximum coarsened phase size was beneficial to avoid the occurrence of the above mentioned harmful factors and was the source of strength stability.