Large Scale Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> (Y<sub>2</sub>O<sub>3</sub>) Eutectic and Hypereutectic Achieved by Combustion Synthesis in High Gravity Field

Abstract

By introducing ZrO2 (4Y) powder into the thermit, the solidified Al2O3-ZrO2 (4Y) ceramic composites with eutectic and hypereutectic microstructures were prepared via combustion synthesis in high gravity field, and the microstructures and mechanical properties of the solidified ceramic composites were discussed. XRD, SEM and EDS showed that the Al2O3-33%ZrO2 (4Y) as the eutectic were composed of random-orientated rod-shaped colonies consisting of a triangular dispersion of orderly submicron-nanometer t-ZrO2 fibers, surrounded by inter-colony regions consisting of spherically-shaped micrometer t-ZrO2 grains, whereas Al2O3-45%ZrO2 (4Y) as the hypereutectic were comprised of spherically-shaped micron-meter t-ZrO2 grains, surround by irregularly-shaped α-Al2O3 grains and a few colonies. Compared to the directionally solidified Al2O3-ZrO2 (Y2O3), the increase in hardness and flexural strength of the eutectic obtained in current experiment was due to high densification, small-size defect and high fracture toughness induced by residual stress toughening and transformation toughening mechanisms; meanwhile, in despite of the moderate decrease in hardness, high flexural strength of the hypereutectic was considered to be a result of small-size defect and high fracture toughness induced by transformation toughening and microcrack toughening mechanisms.