C. Kaya et al /Journal of the European Ceramic Society 23(2003)935-94 I wt% Boehmite 1 wt Glycer I wt %o Celacol Sol derived rsed in water Paste A AL,O paste B 卡ZrO2 ronia powder(30 nm) + Dispersed in water 16 mm days milling for 2 16 mm First Feedrod ronia sol B Vacuum filtering 40-45 wt solids Each monofilament size First Extrudate Pressure filtration Sol-derived past 4 mm Extrusion Second Feedrod Fig. 2. Flow cha he preparation of zirconia sol-derived paste parameters that describes the paste flow during extru- sion are o. the die entry yield stress; To the die wall shear stress; a, and B, the die entry and die land velocity Each monofilament size Second Extrudate coefficients. The m and n are the die entry and die land velocity exponents; these are used to describe non-linear pressure versus velocity data 2.4. Multiphase green body formation by multiple co- Third Feedrod extrusion The flow chart for multiphase green body formation using multiple co-extrusion, is shown in Fig. 3. As Each monofilament size shown in the monofilament extrusion section, square shaped (4x 4 mm) boehmite and zirconia monofilaments were first extruded separately. Then a total of 16 mono- Fig 3. Schematic representation of multiphase component fabrication filaments( 8 boehmite and 8 zirconia) were un-coated or dip coated with zirconia before they are layed-up in a square die. After the first co-extrusion, each co-extruded conia filaments were first produced with zirconia interface filament included 16 filaments and filament size was These multiple co-extruded and plastically deformable zir reduced from 4 to I mm using a 4 mm square die. 22 For conia coated filaments were layered (two or three multiple the second co-extrusion, the same process was repeated co-extruded filaments in each layer) in a rectangular die and the twice co-extruded filament included 256 mono- (70x 12x50 mm)and then pressed using an applied load filaments(128 boehmite and 128 alumina) having a of 10 kN. If two layers of multiple co-extruded filaments filament size of 250 um. After the third stage co-extru- were pressed in the die, the final test plaque layers, the sion, each extruded filament contained 4096 filaments and 24 546 filaments whilst in the case of three layers, the filament size of 62.5 um. During each step of this process, number of filaments within the test plaque was 36864 a zirconia interface was applied, using dip coating. Manu- facture of the multiphase consolidated test plaques with 2.5. Monofilament coating with ZrOz zirconia interfaces using die pressing was carried out, as shown in the multiphase green body formation section in In order to prepare a low solids -loading zirconia sus Fig 3. For this aim, 3rd stage co-extruded boehmite/zir- pension suitable for coating, Degussa zirconia powdersparameters that describes the paste flow during extru￾sion are o the die entryyield stress; o the die wall shear stress; , and , the die entryand die land velocity coefficients. The m and n are the die entryand die land velocityexponents; these are used to describe non-linear pressure versus velocitydata. 2.4. Multiphase green body formation by multiple co￾extrusion The flow chart for multiphase green bodyformation using multiple co-extrusion, is shown in Fig. 3. As shown in the monofilament extrusion section, square shaped (44 mm) boehmite and zirconia monofilaments were first extruded separately. Then a total of 16 mono- filaments (8 boehmite and 8 zirconia) were un-coated or dip coated with zirconia before theyare layed-up in a square die. After the first co-extrusion, each co-extruded filament included 16 filaments and filament size was reduced from 4 to 1 mm using a 4 mm square die.22 For the second co-extrusion, the same process was repeated and the twice co-extruded filament included 256 mono- filaments (128 boehmite and 128 alumina) having a filament size of 250 mm. After the third stage co-extru￾sion, each extruded filament contained 4096 filaments and a filament size of 62.5 mm. During each step of this process, a zirconia interface was applied, using dip coating. Manu￾facture of the multiphase consolidated test plaques with zirconia interfaces using die pressing was carried out, as shown in the multiphase green bodyformation section in Fig. 3. For this aim, 3rd stage co-extruded boehmite/zir￾conia filaments were first produced with zirconia interface. These multiple co-extruded and plasticallydeformable zir￾conia coated filaments were layered (two or three multiple co-extruded filaments in each layer) in a rectangular die (701250 mm3 ) and then pressed using an applied load of 10 kN. If two layers of multiple co-extruded filaments were pressed in the die, the final test plaque contained 24 546 filaments whilst in the case of three layers, the number of filaments within the test plaque was 36 864. 2.5. Monofilament coating with ZrO2 In order to prepare a low solids-loading zirconia sus￾pension suitable for coating, Degussa zirconia powders Fig. 2. Flow chart for the preparation of zirconia sol-derived paste. Fig. 3. Schematic representation of multiphase component fabrication bymultiple co-extrusion. C. Kaya et al. / Journal of the European Ceramic Society 23 (2003) 935–942 937