Near net-shape manufacturing of alumina/zirconia high temperature ceramics with fine scale aligned multiphase microstructures using co-extrusion

Structural materials capable of operating up to 1400 °C, in air and without cooling, are produced using sol-based technology which involves the extrusion, at room temperature, of a two-phase material (Al2O3/ZrO2) resulting in an aligned bi-phase structure which is then multiple re-extruded to reduce the widths of the phases. Two sol-based pastes (of differing chemistry) are co-extruded in parallel, and layed-up in closed-packed linear array to form a heterogeneous macro-plug for subsequent extrusion. The second and third extrusion steps produce a filament with markedly reduced lateral paste dimensions provided that the flow properties of the chemically different pastes are similar. The resulting extrudates that are in the form of continuous green monofilaments are subsequently laid up in a mould where the structure is pressed and consolidated into the desired shape, and then pressureless sintered in air to form the multiphase component. The developed process allows the microstructure to be controlled at a nanometer scale within each extruded filament. It is also demonstrated that this novel process is a powerful tool to obtain damage-tolerant components if the green monofilaments are coated with ZrO2 prior to each step of extrusion and lay-up.