A.J. Sanchez-Herencia et al /Composites: Part B 37(2006)499-508 a)000长x 0.0 0.10 0.15 0.20 A-5YTzP(1)「D=59.4%) A-40YTZP(2)(TD=535% 8009001000110012001300140015 T(C) (b)0.00 -2.0x10 -0.10 40×x104与 0.15 A5YTZP(2)(TD=56.1% -025 800900100011001200130014001500 T(°c) Sintering behavior of A-5YTZP and A-40YTZP monolithic samples. Dilatometric cuves and sintering kinetics for(a) samples with different densities(PA- and(b)samples with similar densities(PA-SYTZP(2)=PA-40YTZP(D)) and A-40YTZP tapes with different green densities (PA- the sintering behavior is very influenced by the packing in 5YTZP()+PA-40YTZP(2) and similar green densities (PA- the green stage. Fig. 4 shows the linear shrinkage and the 5YTZP(2)-PA-40YTZP(I sintering rate curves recorded for the monoliths of the same Fig. 3 shows the strain-stress curves for the layered compositions as those of the layers in the laminates. In material (PA-5YTZP()+PA-40YTZP(2). It can be seen that Fig. 4a, curves for materials with very different green strains as high as 30% can be achieved by working with densities are plotted. It can be seen that sintering started at wet tapes and no inflexion point is detected indicating that similar temperature for both materials, and that the the sample maintains its structural integrity in all the range dilatometric curves run clos to1150°C. After this of pressures. Very similar behavior was observed for the temperature, they shrank in a different way giving a final laminate made with tapes with similar green densities. For shrinkage of 17% for A-5YTZP(I) and 22% for the monolithic and laminated materials described above, a A-40YTZP(2). Also the maximum sintering rate wa ressure of 18 MPa was selected using a 5 wt% dilution of achieved at different temperatures (1400Cfor binder as a gluing agent, as it has been appointed from A-40YTZP(2)and 1460C for A-5YTZP(I). On the other Table 4 hand, the samples with similar green densities(Fig. 4b showed different sintering behavior at low temperatures but 3. 2. Sintering optimization of the laminate finally they achieved similar shrinkages at 1350C, and continued together until a final shrinkage around 20% was The fabrication of multilayer ceramics from powder reached. Also the maximum sintering rate was located at processing techniques involves the co-sintering of green close temperatures(1410C for A-40YTZP(1) and 1425C joined layers. This is a critical point in order to obtain crack for A-5YTZP(2)). The differences in the shrinkage and free layers. Different compositions sinter in different ways sintering rate of the different layers are made evident in the and stresses can be developed between layers if shrinkage microstructure of the samples. Fig. 5a shows a tunneling levels and rates are very different. In this sense, crack developed in a A-40YTZP(2)layer during sintering ofand A-40YTZP tapes with different green densities (rA- 5YTZP(1)srA-40YTZP(2)) and similar green densities (rA- 5YTZP(2)zrA-40YTZP(1)). Fig. 3 shows the strain–stress curves for the layered material (rA-5YTZP(1)srA-40YTZP(2)). It can be seen that strains as high as 30% can be achieved by working with wet tapes and no inflexion point is detected indicating that the sample maintains its structural integrity in all the range of pressures. Very similar behavior was observed for the laminate made with tapes with similar green densities. For the monolithic and laminated materials described above, a pressure of 18 MPa was selected using a 5 wt% dilution of binder as a gluing agent, as it has been appointed from Table 4. 3.2. Sintering optimization of the laminate The fabrication of multilayer ceramics from powder processing techniques involves the co-sintering of green joined layers. This is a critical point in order to obtain crack free layers. Different compositions sinter in different ways and stresses can be developed between layers if shrinkage levels and rates are very different. In this sense, the sintering behavior is very influenced by the packing in the green stage. Fig. 4 shows the linear shrinkage and the sintering rate curves recorded for the monoliths of the same compositions as those of the layers in the laminates. In Fig. 4a, curves for materials with very different green densities are plotted. It can be seen that sintering started at similar temperature for both materials, and that the dilatometric curves run close up to 1150 8C. After this temperature, they shrank in a different way giving a final shrinkage of 17% for A-5YTZP(1) and 22% for A-40YTZP(2). Also the maximum sintering rate was achieved at different temperatures (1400 8C for A-40YTZP(2) and 1460 8C for A-5YTZP(1)). On the other hand, the samples with similar green densities (Fig. 4b) showed different sintering behavior at low temperatures but finally they achieved similar shrinkages at 1350 8C, and continued together until a final shrinkage around 20% was reached. Also the maximum sintering rate was located at close temperatures (1410 8C for A-40YTZP(1) and 1425 8C for A-5YTZP(2)). The differences in the shrinkage and sintering rate of the different layers are made evident in the microstructure of the samples. Fig. 5a shows a tunneling crack developed in a A-40YTZP(2) layer during sintering of Fig. 4. Sintering behavior of A-5YTZP and A-40YTZP monolithic samples. Dilatometric cuves and sintering kinetics for (a) samples with different densities (rA- 5YTZP(1)srA-40YTZP(2)) and (b) samples with similar densities (rA-5YTZP(2)zrA-40YTZP(1)). A.J. Sa´nchez-Herencia et al. / Composites: Part B 37 (2006) 499–508 505