INFLUENCE OF Y2O3 ADDITION ON SUPERPLASTIC CHARACTERISTICS OF AL2O3-20 AND AL2O3-30 MASS-PERCENT-ZRO2 COMPOSITES

The effects of the additional amount of Y2O3 into ZrO2 on the superpla stic characteristics of Al2O3-20 and 30 mass%ZrO2 composites containin g 0, 2, 4 and 6 mol%Y2O3 respectively were considered from experimenta l results carried out by tensile tests at 1400, 1450 and 1500 degrees C and at initial strain rates from 3.33 x 10(-5) to 1.11 x 10(-3) s(-1 ). The obtained main results were as follows. (1) The values in elonga tion of most of the Al2O3-30 mass%ZrO2 composites were generally large r than those of the Al2O3-20 mass%ZrO2 composites. A maximum elongatio n 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%Zr O2 composites containing 4 mol%Y2O3 indicated the largest elongation r esulting from the finer grain size, more uniform distribution between Al2O3 and ZrO2 phases and less microstructural defects such as voids o r cracks. (3) As a reason why the grain size of the composites contain ing 4 mol%Y2O3 was so small and stable during hot deformation, it is p ointed 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 a ere considered to exhibit larger elongations.