Microstructure of directionally solidified Al2O3/EAG eutectic ceramics prepared with high-temperature gradient

Abstract Directionally solidified Al2O3/Er3Al5O12 (EAG) eutectic ceramics are characterized by high melting point, improved high-temperature flexural strength, and high fracture toughness. Therefore, they have recently attracted considerable attention as candidates for high-temperature (>1500 °C) structural materials. In this work, directionally solidified Al2O3/EAG eutectic ceramics were prepared by the optical floating zone technique. 2D and 3D microstructures were observed by scanning electron microscopy and X-ray computerized tomography. The effect of thermal gradient and the solidification rate on Al2O3/EAG eutectic microstructure was investigated. The microstructure was completely irregular, exhibiting 3D interconnected microstructure. The size of eutectic microstructure decreased with increasing growth rate. Stable coupled-growth can be obtained when the solidification rate is less than 60 mm/h. Fracture toughness of Al2O3/EAG eutectic ceramics prepared with a withdrawal rate of 40 mm/h, measured by indentation tests, was KIC = 5.7 ± 0.3 MPa m1/2 and the hardness was HV = 14.5 ± 0.4 GPa. Interfaces between Al2O3 and the EAG phases play important role in improving fracture toughness. The characterization of microstructure and mechanical properties of Al2O3/EAG eutectic ceramics may provide guidance for microstructure design and reveal the deformation mechanisms of Al2O3/EAG eutectic ceramics.