Mechanical Properties and Characterization of ZrO₂-Al₂O₃ Composites with High Fracture Strength

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 MPam^1/2 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.