Abstract
ZrO2-Al2O3 composites with high fracture strength were developed. The maximum bending strength occured at the addition of 20-40 wt% Al2O3 and reached about 3000MPa. Fracture toughness measured by SEPB method showed the same trend as bending strength and was about 7.5 MPam1/2 at the addition of 20-40 wt% Al2O3. And then, each of large Al2O3 grains was dispersed in the matrix of ZrO2 with small grains.
The addition of Al2O3 reduced the crystal grain size of tetragonal ZrO2 and caused the residual stresses due to the thermal expansion mismatch between ZrO2 and Al2O3. Tensile stress in ZrO2 grains and compressive stress in Al2O3 grains were observed. These residual stresses led to the strengthening of Al2O3 grains and the fracture mode change from inter-granular to trans-granular fracture at ZrO2 grains. From above-mentioned results, it was considered that the enhancement of fracture strength resulted in the increase of fracture toughness, the rise of critical stress to initiate tetragonal to monoclinic ZrO2 transformation and the reduction of flaw size.
