Development of nano-composite microstructures in ZrO₂-Al₂O₃ via the solution precursor method

Abstract

Aqueous mixtures of zirconium acetate and aluminum nitrate were pyrolyzed and crystallized to form a metastable solid solution, Zr_1-xAl_xO_2-x/2 (x < 0.57). The initial, metastable phase partitions at higher temperatures to form two metastable phases, viz., t-ZrO₂+γ -Al₂O₃ with a nano-scale microstructure. The microstructural observations associated with the - γ-→α-Al₂O₃ phase transformation in the t-ZrO₂ matrix are reported for compositions containing 10, 20, and 40 mol% A1₂O₃. During this phase transformation, the α-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 A1₂O₃ and the heat treatment conditions influence the final microstructure. At lower volume fractions of A1₂O₃, the colonies coarsen to single, irregular plates, surrounded by polycrystalline ZrO₂. Interpenetrating microstructures produced at high volume fractions of A1₂O₃ exhibit very little grain growth for periods up to 24 h at 1400°C.