A.J. Sanchez Herencia et al. Composites: Part B 37(2006)499-508 aspect similar to a crack partially healed into the A-5YTZP(I) Fig. 8 is the main conclusion of this work: dense multilayer ceramics with strong joining between layers and free of defects can be obtained by stacking water-based tapes and pressure less sintering. The use of wet tapes and a glue agent, with the same composition that the tape binder, avoids defects in the stacks due to the pressure and allows the use of higher pressures than with dry tapes. By controlling the solid content of the startin slurries, it is possible to control the final green density of the tapes and consequently the shrinkage and sintering rate of the layers that compose the laminate. The differential sintering between layers develops tunneling cracks that extend into the tapes that supposedly are under compression. If tapes with the appropriate green density are selected, stresses due to sinterin ell as the associated defects can be avoided This work has been supported by Comunidad de madrid project GRMAT 0707-2004 and by CiCYT project MAT2003- 00836 and partly by the Europan Communitys Human Potential programme under contract HPRN-CT-2002-00203 (SICMAC). Jonas Gurauskis acknowledges the financial upport provided by the Europan Communitys Human Potential programme under contract HPRN-CT-2002-00203 Fig. 7. SEM micrographs at the cross-section of laminated samples obtained (SICMAC) from tapes with different green densities showing(a) the aspect of tunneling crack in A-40YTZP(2) layer and( b) a close up to the low density zone into A-5YTZP(1)layer. References [1] Lange FF. Powder processing science and technology for increased liability. J Am Ceram Soc 1989:72(1): 3-15 [2 Weiner S, Addadi L. Design strategies in mineralized biological materials. J Mater Chem 1997: 7(5): 689-702. [3] Aksay IA, Sarikaya M. Bioinspired processing of composite materials. In: Ceramics toward the 21st century. Tokyo: The Ceramic Society of Japan 1991.p.136-9 [4] Pyzik AJ, Aksay IA. Microdesign of B4C-Al cermets. In: Proceeding of 'oPamic and metal matrix composites. New York, NY: Pergamon Press, [5] Schwartz B, Wilcox DL. Laminated ceramics Ceram Age 1967: 83(6 Ceram Soc Bull 1972: 51(5): 482-5 [7] Mistler RE. High-strength alumina substrates produced by a multiple- layer casting technique. Am Ceram Soc Bull 1973: 52(11): 850-4 [8 Russo C, Harmer MP, Chan HM, Miller GA Desig eramic composite for improved strength and toughness. J Am Ceram Soc 1992;75(12)3396-400 [9] Clegg wJ, Kendall K, Alford NM, Button Tw. Birchall JD. A simple way to make tough ceramics. Nature 1990: 347(6292): 455-7. 58m [10] Katsuki H, Ichinose H, Shiraishi A, Takagi H, Hirata Y. Preparation and fracture characteristic of laminated alumina mullite composite. Nippon Seram Kyo Gak1993:101(9):1068-70. 8. General view of a crack free A-5YTZP(2)A-40YTZP(1) laminate [11 Davis JB, Kristoffersson A, Carlstrom E, Clegg wJ. Fabrication and crack fuced by gluing, piling up and pressing wet layers obtained by a water- deflection in ceramic laminates with porous interlayers. J Am Ceram Soc 2000;83(10):2369-74aspect similar to a crack partially healed into the A-5YTZP(1) layer. 4. Conclusions Fig. 8 is the main conclusion of this work: dense multilayer ceramics with strong joining between layers and free of defects can be obtained by stacking water-based tapes and pressure less sintering. The use of wet tapes and a glue agent, with the same composition that the tape binder, avoids defects in the stacks due to the pressure and allows the use of higher pressures than with dry tapes. By controlling the solid content of the starting slurries, it is possible to control the final green density of the tapes and consequently the shrinkage and sintering rate of the layers that compose the laminate. The differential sintering between layers develops tunneling cracks that extend into the tapes that supposedly are under compression. If tapes with the appropriate green density are selected, stresses due to sintering as well as the associated defects can be avoided. Acknowledgements This work has been supported by Comunidad de Madrid project GRMAT 0707-2004 and by CICYT project MAT2003- 00836 and partly by the Europan Community’s Human Potential Programme under contract HPRN-CT-2002-00203 (SICMAC). Jonas Gurauskis acknowledges the financial support provided by the Europan Community’s Human Potential Programme under contract HPRN-CT-2002-00203 (SICMAC). References [1] Lange FF. Powder processing science and technology for increased reliability. J Am Ceram Soc 1989;72(1):3–15. [2] Weiner S, Addadi L. Design strategies in mineralized biological materials. J Mater Chem 1997;7(5):689–702. [3] Aksay IA, Sarikaya M. Bioinspired processing of composite materials. In: Ceramics toward the 21st century. Tokyo: The Ceramic Society of Japan; 1991. p. 136–9. [4] Pyzik AJ, Aksay IA. Microdesign of B4C-Al cermets. In: Proceeding of ceramic and metal matrix composites. New York, NY: Pergamon Press; 1989. p. 169–80. [5] Schwartz B, Wilcox DL. Laminated ceramics. Ceram Age 1967;83(6): 40–4. [6] Ettre K, Castles GR. Pressure-fusible tapes for multilayer structures. Am Ceram Soc Bull 1972;51(5):482–5. [7] Mistler RE. High-strength alumina substrates produced by a multiple￾layer casting technique. Am Ceram Soc Bull 1973;52(11):850–4. [8] Russo CJ, Harmer MP, Chan HM, Miller GA. Design of a laminated ceramic composite for improved strength and toughness. J Am Ceram Soc 1992;75(12):3396–400. [9] Clegg WJ, Kendall K, Alford NM, Button TW, Birchall JD. A simple way to make tough ceramics. Nature 1990;347(6292):455–7. [10] Katsuki H, Ichinose H, Shiraishi A, Takagi H, Hirata Y. Preparation and fracture characteristic of laminated alumina mullite composite. Nippon Seram Kyo Gak 1993;101(9):1068–70. [11] Davis JB, Kristoffersson A, Carlstrom E, Clegg WJ. Fabrication and crack deflection in ceramic laminates with porous interlayers. J Am Ceram Soc 2000;83(10):2369–74. Fig. 8. General view of a crack free A-5YTZP(2)/A-40YTZP(1) laminate produced by gluing, piling up and pressing wet layers obtained by a water￾based tape casting. Fig. 7. SEM micrographs at the cross-section of laminated samples obtained from tapes with different green densities showing (a) the aspect of tunneling crack in A-40YTZP(2) layer and (b) a close up to the low density zone extension into A-5YTZP(1) layer. A.J. Sa´nchez-Herencia et al. / Composites: Part B 37 (2006) 499–508 507