Sintering densification and microstructure formation of bulk Al₂O₃/YAG eutectic ceramics by hot pressing based on fine eutectic structure

Highly-dense Al₂O₃/YAG bulk eutectic ceramics with fine irregular eutectic structure are produced by a facile way of hot pressing method based on a unique micro-eutectic structure. The densification behavior and microstructure formation are investigated. The eutectic particles with different sizes (<4μm, 4-10μm, <25μm) and homogenous micro-eutectic structure are first prepared by pulverizing Al₂O₃/YAG eutectic rods solidified by laser floating zone and then are consolidated by hot pressing under different sintering temperatures (1450-1650°C). The results show that the initial eutectic particle size and sintering temperature importantly affect the full-eutectic structure formation during hot pressing. Using the sintering temperature above 1650°C and eutectic particles of 4-10μm, dense bulk eutectic ceramics (99.1%) are obtained, particularly well remaining the initial eutectic structure without grain boundaries, comparable to eutectic ceramics prepared by melt growth method. The <25μm and <4μm eutectic particles are preferred to achieve higher densification (>99.5%) but are difficult to reproduce repeatable full-eutectic microstructure in whole composite. Moreover, the formation mechanism of the full-eutectic structure for the ceramics by sintering is discussed. This method paves a facile and cost-effective way to manufacture near net shaped large bulk eutectic ceramics for applications at elevated temperatures.