Microstructure Transformation and Mechanical Properties of the Large-Bulk Solidified Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> (Y<sub>2</sub>O<sub>3</sub>) Micro-Nanocrystalline Composites Prepared by Combustion Synthesis under High Gravity

Abstract

Based on preparing the large-bulk solidified Al2O3-ZrO2 (Y2O3) ceramic composites by combustion synthesis under high gravity, the solidification behavior and microstructure transformation of the ceramics as well as their effects on the ceramic properties were investigated. XRD, SEM and EDS analyses showed the ceramic microstructures were composed of the irregular eutectics at the surface and the tetragonal ZrO2 micrometer spherical crystals in the center of the ceramics respectively. By combining with irreversible nucleation theory, it is considered that the formation of irregular eutectics with micro-nanocrystalline microstructures is a result of the leading nucleation of Al2O3 high-fusion-entropy phases followed by the coupled growth of Al2O3-ZrO2 phases, whereas the presence of the tetragonal ZrO2 spherical microstructures in the center of the ceramics results from the leading nucleation of ZrO2 cubic phases followed by the independent growth of Al2O3-ZrO2 phases. As a result, it is just the unique microstructure transformation during the solidification process that the highest hardness at the surface and the highest fracture toughness in the center of the ceramics are achieved respectively.