Co-extrusion of Al2O3/ZrO2 bi-phase high temperature ceramics with fine scale aligned microstructures

Structural ceramic composites comprising continuous fibrillar microstructure 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 co-extruded to reduce the lateral dimensions of the phases. Two sol-derived pastes of differing chemistry (gamma-AlOOH as alumina source and zirconia) are co-extruded in parallel, and layed-up in closed-packed linear array to form a heterogeneous macro-plug for subsequent extrusion with or without zirconia coating. 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 in the form of continuous green monofilaments, are subsequently laid up in a mould where the structure is pressed and consolidated in desired shape, then pressureless sintered in air to form the multi-phase component. The developed process allows the microstructure to be controlled at a nanometer scale within each extruded filament and after the 3rd stage coextrusion, each filament size within the final extrudate is reduced to similar to 65 mum. (C) 2002 Elsevier Science Ltd. All rights reserved.