Abstract
The crystal phase and mechanical properties of 2.0 to 3.5 mol% Y2O3-stabilized zirconia polycrystals sintered from agitator milled powders (solid phase mixing, SPM) were investigated. Powders containing 2.5 and 2.8 mol% Y2O3 showed higher sinterability than those containing 2.0 and 3.5 mol% Y2O3. The thermal expansion curve of the 2.5 and 2.8 mol% Y2O3 samples exhibited a monoclinic to tetragonal phase transformation during the heating stage, with a linear relationship observed during cooling. However, a hysteresis was not observed during the heating and cooling stages when the Y2O3 content and sintering temperature were increased. The 2.0 mol% Y2O3 sample exhibited the transformation and hysteresis, even though the sintering temperature was increased. The relationship between the flexural strength and grain size for the sample with 2.0 mol% Y2O3 was not linear, but exhibited a peak. The flexural strength of the 2.5 and 2.8 mol% Y2O3 samples increased as the grain size increased, and then over a certain grain size the flexural strength remained constant and independent of the grain size. The flexural strength and fracture toughness of the 2.0 mol% Y2O3 sample might be dominated by microcrack-toughening. On the other hand, those for the 2.5 and 2.8 mol% Y2O3 samples were dependent not only on the stress-induced transformation, but also on the compressive residual stress and microcrack-toughening caused by the transformation. The relationship between the fracture toughness and Vf √h, where Vf is the tetragonal phase fraction and h is the transformation depth, for the 2.0, 2.5 and 3.5 mol% Y2O3 samples was non-linear and exhibited a peak; however, that for the 2.8 mol% Y2O3 sample was linear.
