Abstract
The effects of the additional amount of Y2O3 into ZrO2 on the superplastic characteristics of Al2O3-20 and 30 mass%ZrO2 composites containing 0, 2, 4 and 6 mol%Y2O3 respectively were considered from experimental results carried out by tensile tests at 1400, 1450 and 1500°C and at initial strain rates from 3.33×10−5 to 1.11×10−3 s−1. The obtained main results were as follows.
(1) The values in elongation of most of the Al2O3-30 mass%ZrO2 composites were generally larger than those of the Al2O3-20 mass%ZrO2 composites. A maximum elongation of 164 and 158% was obtained for each Al2O3-30 mass%ZrO2 (4 mol%Y2O3) and Al2O3-20 mass%ZrO2 (4 mol%Y2O3) composite respectively.
(2) The microstructural observation revealed that both Al2O3-20 and 30 mass%ZrO2 composites containing 4 mol%Y2O3 indicated the largest elongation resulting from the finer grain size, more uniform distribution between Al2O3 and ZrO2 phases and less microstructural defects such as voids or cracks.
(3) As a reason why the grain size of the composites containing 4 mol%Y2O3 was so small and stable during hot deformation, it is pointed out that their microstructures consisting of the dual phases of t and c were smaller than those of a single t phase in the composites containing 2 mol%Y2O3. Also these smaller ZrO2 grains were dispersed among Al2O3 grains by a pinning effect, then the composites containing 4 mol%Y2O3 were considered to exhibit larger elongations.
