Development of Nano‐Composite Microstructures in ZrO ₂ ‐Al ₂ O ₃ 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‐ x Al x O 2− x /2 ( x < 0.57). The initial, metastable phase partitions at higher temperatures to form two metastable phases, viz., t −ZrO 2 +γ‐Al 2 O 3 with a nano‐scale microstructure. The microstructural observations associated with the γ‐ →α‐Al 2 O 3 phase transformation in the t ‐ZrO 2 matrix are reported for compositions containing 10, 20, and 40 mol% A1 2 O 3 . During this phase transformation, the α‐Al 2 O 3 grains take the form of a colony of irregular, platelike grains, all with a common crystallographic orientation. The plates contain ZrO 2 inclusions and are separated by ZrO 2 grains. The volume fraction of A1 2 O 3 and the heat treatment conditions influence the final microstructure. At lower volume fractions of A1 2 O 3 , the colonies coarsen to single, irregular plates, surrounded by polycrystalline ZrO 2 . Interpenetrating microstructures produced at high volume fractions of A1 2 O 3 exhibit very little grain growth for periods up to 24 h at 1400°C.