C. Kaya et al /Journal of the European Ceramic Society 23(2003)935-94 sae 1i:9 Fig. 10. SEM images of a zirconia coated monofilament, showing(a)the homogeneous zirconia layer around the filament, (b)the thickness of the zirconia layer to be about 10 um and(c) the propagation of an indenter-induced crack at the alumina/ zirconia interface(A: alumina and z: zirconia) is about 10 um as shown in Fig. 10(b). These pictures the two pastes, drying and sintering shrinkage are both clearly show the effectiveness of the dip-coating process optimised and controlled in order to eliminate the crack which relies on the strong electrostatic attraction formation within the filaments or at the interface. 3rd between the coating sol particles and extrudate surface. co-extrusion provides a filament size of about 60-70 um The propagation of an indenter induced crack on a co- and these plastically deformable co-extruded filaments extruded filament with zirconia interface is shown in in green state are layed up in desired shape mold to Fig. 10(c). It is shown that the zirconia interface created produce net shape components. The final pressureless between alumina and zirconia phases within the co- sintered (1400C for 2 h)alumina and zirconia micro- extruded filament is able to deflect the crack along the structures within the co-extruded matrix are very fine boundary. (the average grain size of alumina and zirconia are determined to be 1.6 and 0.45 um, respectively) and pore free. This processing technique allows us to pro 4. Conclusions duce damage-tolerant components with the application of zirconia interface during co-extrusion or lay up stages This work introduces a new method of fabricating in the final mold diphasic ceramic microstructures with controlled phase dimensionality and anisotropy provided by thin paralle arrays(microlaminae) of 2 thermodynamically-compa- Acknowledgements tible ceramic pastes (boehmite/zirconia). Multiphase alumina/zirconia components were produced from This project is supported by the European Commis nano-size sol-derived pastes using co-extrusion. The sion under the contract number BRITE- EURAM feasibility of forming multiphase aligned fibrilar micro- BRPR-CT 97-0609. Project partners; University of structures using the innovative co-extrusion process Warwick (UK), Morgan Materials Technology, M-T developed is shown to be achiaviable if the rheology of (UK), Centro de estudios e Investigaciones, CEITis about 10 mm as shown in Fig. 10(b). These pictures clearlyshow the effectiveness of the dip-coating process which relies on the strong electrostatic attraction between the coating sol particles and extrudate surface. The propagation of an indenter induced crack on a co￾extruded filament with zirconia interface is shown in Fig. 10(c). It is shown that the zirconia interface created between alumina and zirconia phases within the co￾extruded filament is able to deflect the crack along the boundary. 4. Conclusions This work introduces a new method of fabricating diphasic ceramic microstructures with controlled phase dimensionalityand anisotropyprovided bythin parallel arrays (microlaminae) of 2 thermodynamically-compa￾tible ceramic pastes (boehmite/zirconia). Multiphase alumina/zirconia components were produced from nano-size sol-derived pastes using co-extrusion. The feasibilityof forming multiphase aligned fibrilar micro￾structures using the innovative co-extrusion process developed is shown to be achiaviable if the rheologyof the two pastes, drying and sintering shrinkage are both optimised and controlled in order to eliminate the crack formation within the filaments or at the interface. 3rd co-extrusion provides a filament size of about 60–70 mm and these plasticallydeformable co-extruded filaments in green state are layed up in desired shape mold to produce net shape components. The final pressureless sintered (1400 C for 2 h) alumina and zirconia micro￾structures within the co-extruded matrix are veryfine (the average grain size of alumina and zirconia are determined to be 1.6 and 0.45 mm, respectively) and pore free. This processing technique allows us to pro￾duce damage-tolerant components with the application of zirconia interface during co-extrusion or layup stages in the final mold. Acknowledgements This project is supported bythe European Commis￾sion under the contract number BRITE- EURAM, BRPR- CT 97- 0609. Project partners; Universityof Warwick (UK), Morgan Materials Technology, M2 T (UK), Centro de Estudios e Investigaciones, CEIT Fig. 10. SEM images of a zirconia coated monofilament, showing (a) the homogeneous zirconia layer around the filament, (b) the thickness of the zirconia layer to be about 10 mm and (c) the propagation of an indenter-induced crack at the alumina/zirconia interface (A: alumina and Z: zirconia). C. Kaya et al. / Journal of the European Ceramic Society 23 (2003) 935–942 941