Rapid solidification and fracture behavior of ternary metastable eutectic Al2O3/YAG/YSZ in situ composite ceramic

Directionally solidified oxide ceramic eutectic in situ composites are promising candidate materials for high-temperature structural applications in oxidizing environments. The rapid solidification characteristics of ternary metastable eutectic composition of Al2O3/YAG/YSZ in situ composite ceramics grown by laser zone-remelting technique are investigated. The fracture toughness and crack propagation behavior of the as-solidified composites are examined by the Vickers indentation technique. The metastable eutectic Al2O3/YAG/YSZ ceramic consists of Al2O3, YAG and YSZ phases, showing a typical ultra-fine irregular lamellar microstructure morphology with eutectic spacing as fine as 0.5 μm. Moreover, the ternary eutectic microstructures with coupled growth characteristics are also formed at the off-eutectic composition, effectively enlarging the eutectic growth range. The mean fracture toughness of the metastable eutectic Al2O3/YAG/YSZ ceramic is 3.9 ± 1.0 MPa m1/2. The addition of ZrO2 which weakens the interface bonding between YAG and Al2O3 phases, crack deflection, branching and microcrack toughening are the predominant toughening mechanisms.