The composites were prepared by ball-milling ZrO2（3%Y2O3） and γ-Al2O3 nanoparticles, pressing unidirectionally, cold-pressing isostatically and pressurelessly sintering in air. The phases of ZrO2 in composites were examined by X-ray diffraction. The microstructure of Al2O3/3Y-TZP composites was observed by scanning electron microscope （SEM） and transmission electron microscopy （TEM） respectively. The X-ray analysis reveals that ZrO2 of both surface and fracture surface is mainly t-ZrO2. The SEM image shows that there are some intragranular particles in large granulars. The fracture toughness K 1c of Al2O3/70%ZrO2（3%Y2O3（mole fraction）） composite tested by single-edge notched bending is 13.5 MPa·m 1/2. Being toughened by the ferroelastic domain switching and the intragranular microstructure explains high toughness of the composite.
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