C. Reynaud et al. International Journal of Refractory Metals Hard Materials 19(2001)425-435 average feret diameter Layered structures without defects have been obtained with parallel layers and uniform thickness(dense layer eigthed mean 70 um; porous layer: 80 um) The last step of our research will be the study rupture behaviour This process, using PFAs to elaborate laminar com- posites, can be transposed to other materials and ce- ramIcs 2 Acknowledgements The authors would like to thank r. Gibert (SPIN center, ENS Mines St-Etienne) for carrying out the !∴: pectrometry of gases produced during the ther mal degradation of PFA 8g88 analysis performed on dense and porous layers of [Clegg wJ, Kendall K, Alford NMcN, Button TW A simple way to make tough ceramics. Nature 1990 wo svm layered composites containing, respectively. 45 and 45 vol% of PA-A. CS corresponds to corn 2Vandeperre L, Van Der Biest O. Composite PL and IPL, are, respectively, the abbreviations of terlayers for crack deflection in ceramic laminates. Silic Ind external dense layer, internal dense layer, external porous layer, in 8:63:39-43 ernal porous laye 3 Blanks Ks, Kristoffersson A, Carlstrom E, Clegg, WJ. Crack deflection in ceramic laminates using porous interlayers. J Eur eram Soc 1998;18:1945-51. 4 Davis JB, Kristoffersson A, Carlstrom E, Clegg, WJ. Fabrication durry. Different PFA with a narrow size distribution and crack deflection in ceramic laminates with porous interlayers. have been used(corn starch and powders of polyamide [5 Liu H, Hsu SM. fracture behavior of multilayer silicon nitride/ 12). Two types of samples have been prepared: mono- boron nitride ceramics. J Am Ceram Soc 1996: 79: 2452-7 lithic blocks and alternate laminates (laminar compo 6 Kovar D, Thouless MD, Halloran Jw. Crack deflection and ites) of dense and porous layers propagation in layered silicon nitride/boron nitride cer J Am Ceram Soc 1998: 81: 1004-12 For each PFA, the porosity attains a maximum value Ohji T, Shigegaki Y, Miyajima T, Kanzaki S. Fracture resistance dependent on the PFA size and nature(41 vol% with behavior of multilayered silicon nitride. J Am Ceram Soc corn starch) 199780:991-4 Only laminates using corn starch present a level of 8 Chartier T, Merle D, Besson JL. Laminar ceramic composites. orosity higher than the theoretical level of porosity J Eur Ceram Soc 1995: 15: 101-7. required to ensure crack deflection. Furthermore the 9 Chartier T, Rouxel T. Tape cast alumina-zirconia laminates: processing and mechanical properties. J Eur Ceram Soc 1997; 17 volumetric shrinkage during sintering for porous mate- 299-308 rial using corn starch is quite constant and is similar to [10] She J, Inoue T, Kazuo U. MultilayerAlOj/SiC cs with that of free PFA materials for PFA content up to 45 proved mechanical behavior. J Eur Ceram Soc 2000: 20: 1771-5 vol% due to the lowest chemical interaction between I Lyckfeldt O, Liden E, Carlsson R. Processing of thermal corn starch and the tape casting additives. No residual insulation materials with controlled porosity. In: Linton DP, Limaye SY, editors. Ceramic transactions Low-exp thermal stresses induced during cooling can be expected ials. The American Ceramic Society: 1995. p. 217- The thermal degradation of corn starch produces a [12] Corbin SF, Apte Ps. Engineered porosity via lower amount of gas than polyamide PFA and is less lamination and the percolation of pyrolysable particulates. J Am Ceram Soc1999:82:1693-701 ensitive to the nature of the gas used during the burn- [13] Baud S, Thevenot F Effect of powder bed composition on liquid ing-out. Consequently, corn starch appears the most phase sintered silicon carbide. In: Vincenzini P, editor. Ninth favourite candidate to elaborate laminar composites Cimtec- World Ceramic Congress Ceramics Getting into the 2000s with engineered porosity Part B. Faenza: Techna: 1999. p. 805-12 Homogeneous distribution of porosity has beer [14 Furnas CC. The relations between specific tained for both monolithic and composites laminates An equiaxed and homogeneous silicon carbide micro- Rep Invest 1928: 2894: 1-10. [5 Zok F, Lange FF, Porter JR. Packing density of composite structure has been obtained and was unaffected by PFA owder mixtures. J Am Ceram Soc 1991: 74: 1880-5. O0
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