Dense Amorphous Zirconia-Alumina by Low Temperature Consolidation of Spray Pyrolyzed Powders

Hot-pressing of metastable amorphous ZrO2-Al2O3 powders was performed at low temperatures (873 and 923 K), under moderately high pressures (500 and 750 MPa), and amorphous pellets with 1 to 8 % porosity were obtained. Crystallization of the amorphous pieces between 1173 and 1673 K produced a range of ultrafine microstructures, the finest of which had 6-8 nm grains of tetragonal (ZrO2-40 mol % Al2O3) solid solution formed at 1173 K. Sub-micron grain sizes of the equilibrium m-ZrO2 and α-Al2O3 are stable against coarsening at 1673 K. The new technique was applied to produce a silicon carbide reinforced composite with an amorphous ZrO2-80 mol % Al2O3 matrix; the high matrix sinterability overcame the reinforcement constraint. The results suggest a possible solution to the difficulties in bulk processing of amorphous, nanocrystalline and other novel ceramics. Based on a poster presented at Ceramics Processing ’97, Santa Barbara, CA, USA (September, 1997)