Sintering densification and microstructure formation of bulk Al_2O_3/YAG eutectic ceramics by hot pressing based on fine eutectic structure

摘要

Highly-dense Al_2O_3/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 (＜4 μm, 4-10 μm, ＜ 25 μm) and homogenous micro-eutectic structure are first prepared by pulverizing Al_2O_3/YAG eutectic rods solidified by laser floating zone and then are consolidated by hot pressing under different sintering temperatures (1450-1650 ℃). 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 ℃ and eutectic particles of 4-10 μm, 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 ＜25 μm and ＜4 μm 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.