| Microstructure and micro-indentation fracture of pressureless-sintered Al₂O₃/ZrO₂(0%Y₂O₃) composite containing different Y₂O₃, content were investigated by transmission and high-resolution electron microscopy. In the Al₂O₃/ZrO₂(0%Y₂O₃) composite, strong strain field contrasts were observed in Al₂O₃ near m-ZrO₂ grains. ZrO₂ with a lamella-shaped twin structure produces compressive and expansive strain field in adjoining Al₂O₃ matrix and microcracks at the interfaces between Al₂O₃ and ZrO₂ with no twins are joined without any impurity phases. However, amorphous phases appear at the interfaces and triple points with increasing Y₂O₃ contents. The main fracture toughening effect in Al₂O₃-ZrO₂(0%Y₂O₃) is due to crack deflection and plastic deformation in m-ZrO₂ grains. In the Al₂O₃/ZrO₂(3%Y₂O₃), main fracture mode is a mixed type with intergranular, and transgranular, and stress-induced phase transformation in tetragonal-ZrO₂ grains partially occurs by crack propagation. In Al₂O₃/ZrO₂(8%Y₂O₃), fracture was mainly transgranular, but serious plastic deformation is not observed in transgranularly fractured cubic-ZrO₂ grains. |
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