Changes in the microstructure and mechanical properties of Al2O3/YSZ directionally solidified eutectic ceramics during long-time heat treatment

Al2O3/YSZ directionally solidified eutectic ceramics (DSECs) were prepared using the induction heating zone melting (IHZM) method. The microstructures of the DSECs formed with various crucible pulling rates (2.5-300 mm/h) changed from the discontinuous lamellar into the colony structure, finally into the cell structure. The intracolony had better microstructural stability than the intercolony during heat treatment due to two factors: the size effect and the t-m transformation effect. The hardness changes were mainly related to the release and generation of residual stress caused by repeated heating and cooling. The quantity of cracks in DSECs increased with the heat treatment time, leading to a gradual decrease in the fracture toughness, 300 mm/h DSEC had the lowest reduction in fracture toughness after 500 h heat treatment due to fine microstructure, the fracture toughness was 7.15 MPa.m(1/2), which was 76 % of that before the heat treatment (9.39 MPa.m(1/2)).