Evolutions of the Microstructure and Mechanical Properties of Al ₂ O ₃ /YAG DSEC During High‐Temperature Heat Treatment

Directionally solidified eutectic ceramic (DSEC) Al ₂ O ₃ /YAG is fabricated with the high frequency induction heated vertical Bridgman method. The evolutions of the microstructure and the mechanical properties are investigated during a long term heat treatment at 1500°C for 100–300 h for the DSEC samples grown at different growth rates (10–30 mm/h). The results show that the eutectic maintains the two‐phase Al ₂ O ₃ and YAG microstructure after the heat treatment. The eutectic spacing increases significantly with the heat treatment time for all the DSECs, and the higher the growth rate at which the sample is grown, the more pronounced the microstructure coarsening. The eutectic spacing of DSEC Al ₂ O ₃ /YAG grown at 30 mm/h HAY(30) increases by 33.4%, much higher than 7.55% by which HAY(10) grown at 10 mm/h. The hardness and fracture toughness of HAY(10) decrease by only 3.6% and 12.7%, respectively, whereas those of HAY(30) decrease by 9.05% and 21.5%, respectively. The samples grown at lower rates exhibit a better thermal stability. Furthermore, the coarsening‐kinetics analysis indicates that the coarsening of Al ₂ O ₃ /YAG DSEC follows a diffusion‐controlled Ostwald ripening mechanism, governed primarily by the interfacial diffusion at the early stage, transitioning to the volume diffusion at the later stage.