Processing, microstructure and performance of Al2O3/Er3Al5O12/ZrO2 ternary eutectic ceramics prepared by laser floating zone melting with ultra-high temperature gradient

Directionally solidified Al2O3/Er3Al5O12(EAG)/ZrO2 ternary eutectic/off-eutectic composite ceramics with high density, homogeneous microstructures, well-oriented growth have been prepared by laser floating zone melting at different solidification rates from 4 to 400µm/s. Uniform and stable melting zone is obtained by optimizing temperature field distribution to keep continuous and stable eutectic growth and prevent from cracks and defects. The as-solidified composite ceramic exhibits complexly irregular eutectic structure, in which the eutectic spacing is rapidly refined but dotted ZrO2 number inside Al2O3 phase is decreased as increasing the solidification rate. The formation mechanism of ZrO2 distributed inside Al2O3 matrix is revealed by examining the depression of solid/liquid interface. Furthermore, after heat exposure 1500°C for 200h, the eutectic microstructure only shows tiny coarsening, which indicates it has excellent microstructural stability. As increasing the ZrO2 content, the fracture toughness can be improved up to 3.5MPam1/2 at 20.6mol% ZrO2.