DEVELOPMENT OF NANO-COMPOSITE MICROSTRUCTURES IN ZRO2-AL2O3 VIA THE SOLUTION PRECURSOR METHOD

Aqueous mixtures of zirconium acetate and aluminum nitrate mere pyrolyzed and crystallized to form a metastable solid solution, Zr1-xAlxO2-x/2 (x less than or equal to 0.57). The initial, metastable phase partitions at higher temperatures to form two metastable phases, viz., t-ZrO2 + gamma-Al2O3 with a nano-scale microstructure. The microstructural observations associated with the gamma- --> alpha-Al2O3 phase transformation in the t-ZrO2 matrix are reported for compositions containing 10, 20, and 40 mol% Al2O3. During this phase transformation, the alpha-Al2O3 grains take the form of a colony of irregular, platelike grains, all with a common crystallographic orientation. The plates contain ZrO2 inclusions and are separated by ZrO2 grains. The volume fraction of Al2O3 and the heat treatment conditions influence the final microstructure. At lower volume fractions of Al2O3, the colonies coarsen to single, irregular plates, surrounded by polycrystalline ZrO2. Interpenetrating microstructures produced at high volume fractions of Al2O3 exhibit very little grain growth for periods up to 24 h at 1400 degrees C.