Auto ignition synthesis and consolidation of Al₂O₃–ZrO₂ nano/nano composite powders

An “Auto Ignition” technique was utilized in synthesizing Al₂O₃ –ZrO₂ powders with nano/nano microstructure. The process used the corresponding nitrates as oxidizers and urea as the fuel. The as-synthesized powders were characterized by x-ray diffraction and transmission electron microscopy. It was observed that the microstructure consisted of crystallites of Al₂O₃ and ZrO₂, both of which were nanocrystalline. As opposed to the other nanocomposite ceramics, this feature of the microstructure classifies the present powders as nano/nano type. This nanocrystallinity of the microstructure (crystallite size less than 100 nm) was maintained even after a soaking at 1200 °C for 2 h. Since the microstructure is stable at high temperatures, it was possible to densify the powders by hot isostatic pressing at 1200 °C. The product was 99% of the theoretical density and maintained nanocrystalline grain size. The average hardness and toughness values, as determined by an indentation technique, were 4.45 GPa and 8.38 MPa · m^1/2, respectively. These values represent evidence of ductility in these composites since transformation toughening was ruled out in this case. The potential application of these results is expected to be in net shape deformation forming of ceramics.