Characterization of Al₂O₃-ZrO₂ powders produced by electrohydrodynamic atomization

Abstract

The roles of supercooling and alloy composition in the microstructure evolution of rapidly solidified powders have been systematically examined across the Al₂O₃-ZrO₂ binary system. Powders ranging in diameter from 10 nm to over 100 μ m were produced by electrohydrodynamic atomization of Al₂O₃-ZrO₂ rods prepared by colloidal techniques. At the largest supercoolings (powders less than 1 μm), single-phase homogeneous structures, both amorphous and crystalline, may be observed across the entire phase diagram. With increasing particle size, segregation gives rise to duplex microstructures which consist of metastable alumina and monoclinic or tetragonal zirconia, or of tetragonal zirconia and glass. Coarse (greater than 10 μm) powders exhibit different morphologies in the primary phase and the eutectic constituent, with varying supercoolings and cooling rates. The trends in phase selection and segregation are examined with the aid of available information on T_g and schematic T₀ curves for the different phases.