MICROSTRUCTURE DEVELOPMENT AND MECHANICAL-PROPERTIES OF Y2O3-DOPED TETRAGONAL ZRO2 POLYCRYSTALS AND MULLITE COMPOSITES

Composites containing Y2O3-doped tetragonal ZrO2 polycrystals (Y-TZP) and mullite were prepared by adding Y-TZP powder to a silicon aluminate sol, which is the precursor of the mullite phase. After filtration and drying, the mixed powder was compacted and sintered at 1500-degrees-C in air for various lengths of time. The mullite particles were uniformly distributed in a Y-TZP matrix; energy-dispersive spectroscopy microanalysis indicated that the chemical composition of these particles ranged from 3Al2O3-2SiO2 to 2Al2O3-SiO2. Incorporating mullite particles in a Y-TZP matrix had two evident effects on the composites: first, the ZrO2 grain size was substantially increased; second, the fracture toughness of the composites showed a 50% increase (from 9 to 13.5 MPa m0.5). This increased toughness was due to the enhanced transformability of the tetragonal ZrO2 (t-ZrO2), which resulted mainly from the enlarged grain size and the increased tetragonality of the t-ZrO2.