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S. Bueno et al. /Journal of the European Ceramic Society 28 (2008)1961-1971 a decrease of the fracture toughness of the material. Neverthe- 10. Bueno, S and Baudin, C, Layered materials with high strength and less, such microcracks could lead to the branching of the main tolerance based on alumina and aluminium titanate. J. Eur Ceram. crack and, consequently, to the increase of the fracture surface, 2007,27,1455-1462. leading to the increase of the total energy consumed during crack 11. Dakskobler, A and Kosmac, T, Preparation and properties of aluminium propagation. This second phenomenon would contribute to the 12 Manurung, P, Low, L M and o' Connor, B H, Effect of beta-spodumene on the phase development in an alumina/aluminium-titanate system Mater high crack driving forces such as thermal shock Res.Bul.,2005,40,2047-2055 13. Taylor, D. Thermal expansion data. XI. Complex oxides, A2 BOs, and the garnets. Br. Ceram. Trans. J., 1987, 86, 1-6. 5. Conclusions 14. Taylor, D, Thermal expansion data. Ill. Sesquioxides, M2O3 with the corun- dum and the A B- and C-M O3 structures. Br. Ceram. Trans. J, 1984, 83 Alumina+10 vol. aluminium titanate composites were 15. Bueno. S. Moreno, R and Baudin, C, Reaction sintered Al2O3/Al2TiOs 92-98 obtained by reaction sintering of alumina and titania. The reac microcrack-free composites obtained by colloidal filtration. J. Eur Ceram. ion sintering process promoted the formation of aluminium Soc.,2004,24.2785-2791 titanate nanometric grains at grain boundaries between the alu- 16. Guinea, G. V, Pastor, J. Y, Planas, J and Elices, M. Stress intensity factor, mina graIn ompliance and CMOD for a general three-point-bend beam. Int J. fract. 1998,89,103-118 as the main toughening mechanism in the composites, which 17 Gogotsi, G A The use of brittleness measure(x)to represent mechanical behaviour of ceramics Ceram. Int. 1989. 15. 127-129 showed significant increments in work of fracture and faw tol- 18.Sakai, M, Yoshimura, J, Goto, Y and Inagaki, M. R-curve behaviour of erance as compared with monophase alumina materials with a polycrystalline graphite: microcracking and grain bridging in the wake similar microstructures egion. J. Am. Ceram. Soc. 1988, 71, 609-616 The classical linear fracture toughness parameters, KIC and 19. Steinbrech R. W, Reichl. A and Schaarwaichter, W.J. R-curve behaviou of long cracks in alumina. J. An. Ceram. Soc. 1990, 73, 2009-2015 IC, have demonstrated not to be adequate to characterize frac- 20. Fett, T. Munz, D, Geraghty, R D and White, K W, Influence of specimen ture of the composites, each fracture parameter analyzed, JIC, R geometry and relative crack size on the R-curve. Eng. Fract. Mech., 2000 curve and work of fracture gave different information about the 66.375-386 fracture behaviour of the material 21. Wachtman, J. B, Stable crack propagation and R-curve behaviour. Mechan- ical Properties of Ceramics. John Willey Sons Inc, New York, NY, 1996, pp.141-15 Acknowledgments 22. Fett, T and Munz D. Evaluation of R-curve effects in ceramics. J Mater Sci.,1993,28,742-752. This work has been supported by the EC Human Poten- 23. Hubner, H and Jillek, w, Sub-critical crack extension and crack resistance tial Programme HPRN-CT-2002-00203, by the Project CICYT 24. Tanaka. K. Akiniwa. Y. Kimachi. H and Kita. YR MAT2006-13480(Spain) and the Postdoctoral Fellowship MEC fracture of notched porous ceramics. Eng. Fract. Mech., 2003, 70, 1101 EX-2006-0555 (Spain 25. Ebrahimi, M. E, Chevalier. J. and Fantozzi, G, R-curve evaluation and bridging stress determination in alumina by compliance analysis. J. Eur References Ceram.Soc.,2003,23,943-949 26. Hashida, T, Li, C. and Takahashi, H, New development of the J-based 1. Harmer, M. P, Chan, H. M. and Miller, G. A, Unique opportunities for fracture testing r ceramic matrix composites. J. Am. Ceram. Soc.,1994,77,1553-156 J.Am.Cerm.Soc,1992,75,1715-1728 27. Homeny, J, Darroudi, T and Bradt, R C, J-integral measurements of the Steinbrech, R. w, Toughening mechanisms for ceramic materials. J. Eur fracture of 50% alumina refractories. J. Am. Ceram Soc. 1980. 63. 326- Ceran.Soc.,1992,10,131-142 3. Evans. A G. P ve on the development of high-toughness ceramics. 28. Rice, J.R, A path independent integral and the approximate analysis 丿Am. Ceram.Soc.,1980,73,187-206 of strain concentration by notches and cracks. J. AppL. Mech., 1968, 3 4. Lawn, B. R, Padture, N. P. Braun, L. M. and Bennison, S.J., Model for 379-386. 29. Stevens, R. N and Guiu, F, The application of the J-integral to problems of Ceran.Soc.,1993,76,2235-2240 crack bridging. Acta Metall. Mater, 1994, 42, 1805-1810 5.Padture,NP Runyan, J. L. Bennison, SJ, Braun, L.M. and Lawn, B. 30. Droillard, C and Lamon, J.J. Fracture toughness of 2-D woven Sic/Sic R. Model for toughness curves in two-phase ceramics. Il. Microstructural CVl-composites with multilayered interphases. J Am Ceram Soc., 1996 variables. J. Am. Ceram Soc. 1993.76.2241-2247 79,849858 6. Padture, N. P. Bennison. S. J. and Chan. H. M. Flaw-tolerance and 31. Bueno, S, Moreno, R and Baudin, C, Design and processing of Al2O3 crack-resistance properties of alumina-aluminium titanate I2TiOs layered structures. J. Eur Ceram Soc., 2005, 25, 847-856 with tailored microstructures. J. Am. Ceram. Soc., 1993, 76. 2312- 32. Fullmann, R. L. Measurement of particle sizes in opaque bodies. Trans AME,J.Met.,1953,197,447. 7. Runyan, I L and Bennison, S J, Fabrication of flaw-tolerant aluminium- 33. Uribe, R and Baudin, C Aluminium titanate formation by solid-state reac tion of alumina and titania. Bol. Soc. Esp Ceram. vid, 2000, 39, 221- 8. Uribe, R. and Baudin, C, Infuence of a dispersion of aluminium titanate 228 particles of controlled size on the thermal shock resistance of alumina. J. 34. wieninger, H, Kromp, k and Pabst, R. F. Crack resistance curves of Am Ceram Soc. 2003. 86.846 alumina and zirconia at room temperature. J Mater. Sci, 1986, 21, 411-418 9.Baudin, C, Sayir, A. and Berger, M. H, Mechanical behaviour of direction- 35. Rice, R. W, Freiman, S. w and Becher, P. F- Grain-size dependence of ally solidified alumina/aluminium titanate ceramics. Acta Mater, 2006, 54, fracture energy in ceramics. I. Experiment. J. Am. Ceram. Soc., 1981, 64 3835-3841.1970 S. Bueno et al. / Journal of the European Ceramic Society 28 (2008) 1961–1971 a decrease of the fracture toughness of the material. Nevertheless, such microcracks could lead to the branching of the main crack and, consequently, to the increase of the fracture surface, leading to the increase of the total energy consumed during crack propagation. This second phenomenon would contribute to the resistance of the materials under loading conditions that imply high crack driving forces such as thermal shock. 5. Conclusions Alumina + 10 vol.% aluminium titanate composites were obtained by reaction sintering of alumina and titania. The reaction sintering process promoted the formation of aluminium titanate nanometric grains at grain boundaries between the alumina grains. This special microstructure led to extensive microcracking as the main toughening mechanism in the composites, which showed significant increments in work of fracture and flaw tolerance as compared with monophase alumina materials with similar microstructures. The classical linear fracture toughness parameters, KIC and GIC, have demonstrated not to be adequate to characterize fracture of the composites, each fracture parameter analyzed, JIC, R curve and work of fracture gave different information about the fracture behaviour of the material. Acknowledgments This work has been supported by the EC Human Potential Programme HPRN-CT-2002-00203, by the Project CICYT MAT2006-13480 (Spain) and the Postdoctoral Fellowship MEC EX-2006-0555 (Spain). References 1. Harmer, M. P., Chan, H. M. and Miller, G. A., Unique opportunities for microstructural engineering with duplex and laminar ceramics composites. J. Am. Ceram. Soc., 1992, 75, 1715–1728. 2. Steinbrech, R. W., Toughening mechanisms for ceramic materials. J. Eur. Ceram. Soc., 1992, 10, 131–142. 3. Evans, A. G., Perspective on the development of high-toughness ceramics. J. Am. Ceram. Soc., 1980, 73, 187–206. 4. Lawn, B. R., Padture, N. P., Braun, L. M. and Bennison, S. J., Model for toughness curves in two-phase ceramics. I. Basic fracture mechanics. J. Am. Ceram. Soc., 1993, 76, 2235–2240. 5. Padture, N. P., Runyan, J. L., Bennison, S. J., Braun, L. M. and Lawn, B. R., Model for toughness curves in two-phase ceramics. II. Microstructural variables. J. Am. Ceram. Soc., 1993, 76, 2241–2247. 6. Padture, N. P., Bennison, S. J. and Chan, H. M., Flaw-tolerance and crack-resistance properties of alumina–aluminium titanate composites with tailored microstructures. J. Am. Ceram. Soc., 1993, 76, 2312– 2320. 7. Runyan, J. L. and Bennison, S. J., Fabrication of flaw-tolerant aluminiumtitanate-reinforced alumina. J. Eur. Ceram. Soc., 1991, 7, 93–99. 8. Uribe, R. and Baudin, C., Influence of a dispersion of aluminium titanate particles of controlled size on the thermal shock resistance of alumina. J. Am. Ceram. Soc., 2003, 86, 846–850. 9. Baudin, C., Sayir, A. and Berger, M. H., Mechanical behaviour of directionally solidified alumina/aluminium titanate ceramics. Acta Mater., 2006, 54, 3835–3841. 10. Bueno, S. and Baudin, C., Layered materials with high strength and flaw tolerance based on alumina and aluminium titanate. J. Eur. Ceram. Soc., 2007, 27, 1455–1462. 11. Dakskobler, A. and Kosmac, T., Preparation and properties of aluminium titanate–alumina composites. J. Mat. Res., 2006, 21, 448–454. 12. Manurung, P., Low, I. M. and O‘Connor, B. H., Effect of beta-spodumene on the phase development in an alumina/aluminium-titanate system. Mater. Res. Bull., 2005, 40, 2047–2055. 13. Taylor, D., Thermal expansion data. XI. Complex oxides, A2BO5, and the garnets. Br. Ceram. Trans. J., 1987, 86, 1–6. 14. Taylor, D., Thermal expansion data. III. Sesquioxides, M2O3 with the corundum and the A-, B- and C-M2O3 structures. Br. Ceram. Trans. J., 1984, 83, 92–98. 15. Bueno, S., Moreno, R. and Baudin, C., Reaction sintered Al2O3/Al2TiO5 microcrack-free composites obtained by colloidal filtration. J. Eur. Ceram. Soc., 2004, 24, 2785–2791. 16. Guinea, G. V., Pastor, J. Y., Planas, J. and Elices, M., Stress intensity factor, compliance and CMOD for a general three-point-bend beam. Int. J. Fract., 1998, 89, 103–118. 17. Gogotsi, G. A., The use of brittleness measure (x) to represent mechanical behaviour of ceramics. Ceram. Int., 1989, 15, 127–129. 18. Sakai, M., Yoshimura, J., Goto, Y. and Inagaki, M., R-curve behaviour of a polycrystalline graphite: microcracking and grain bridging in the wake region. J. Am. Ceram. Soc., 1988, 71, 609–616. 19. Steinbrech, R. W., Reichl, A. and Schaarwachter, W. J., R-curve behaviour ¨ of long cracks in alumina. J. Am. Ceram. Soc., 1990, 73, 2009–2015. 20. Fett, T., Munz, D., Geraghty, R. D. and White, K. W., Influence of specimen geometry and relative crack size on the R-curve. Eng. Fract. Mech., 2000, 66, 375–386. 21. Wachtman, J. B., Stable crack propagation and R-curve behaviour. Mechanical Properties of Ceramics. John Willey & Sons Inc., New York, NY, 1996, pp. 141–157. 22. Fett, T. and Munz, D., Evaluation of R-curve effects in ceramics. J. Mater. Sci., 1993, 28, 742–752. 23. Hubner, H. and Jillek, W., Sub-critical crack extension and crack resistance ¨ in polycrystalline alumina. J. Mater. Sci., 1977, 12, 117–125. 24. Tanaka, K., Akiniwa, Y., Kimachi, H. and Kita, Y., R-curve behaviour in fracture of notched porous ceramics. Eng. Fract. Mech., 2003, 70, 1101– 1113. 25. Ebrahimi, M. E., Chevalier, J. and Fantozzi, G., R-curve evaluation and bridging stress determination in alumina by compliance analysis. J. Eur. Ceram. Soc., 2003, 23, 943–949. 26. Hashida, T., Li, C. and Takahashi, H., New development of the J-based fracture testing technique for ceramic matrix composites. J. Am. Ceram. Soc., 1994, 77, 1553–1561. 27. Homeny, J., Darroudi, T. and Bradt, R. C., J-integral measurements of the fracture of 50% alumina refractories. J. Am. Ceram. Soc., 1980, 63, 326– 331. 28. Rice, J. R., A path independent integral and the approximate analysis of strain concentration by notches and cracks. J. Appl. Mech., 1968, 35, 379–386. 29. Stevens, R. N. and Guiu, F., The application of the J-integral to problems of crack bridging. Acta Metall. Mater., 1994, 42, 1805–1810. 30. Droillard, C. and Lamon, J. J., Fracture toughness of 2-D woven SiC/SiC CVI-composites with multilayered interphases. J. Am. Ceram. Soc., 1996, 79, 849–858. 31. Bueno, S., Moreno, R. and Baud´ın, C., Design and processing of Al2O3- Al2TiO5 layered structures. J. Eur. Ceram. Soc., 2005, 25, 847–856. 32. Fullmann, R. L., Measurement of particle sizes in opaque bodies. Trans. AIME, J. Met., 1953, 197, 447. 33. Uribe, R. and Baudin, C., Aluminium titanate formation by solid-state reaction of alumina and titania. Bol. Soc. Esp. Ceram. Vidr., 2000, 39, 221– 228. 34. Wieninger, H., Kromp, K. and Pabst, R. F., Crack resistance curves of alumina and zirconia at room temperature. J. Mater. Sci., 1986, 21, 411–418. 35. Rice, R. W., Freiman, S. W. and Becher, P. F., Grain-size dependence of fracture energy in ceramics. I. Experiment. J. Am. Ceram. Soc., 1981, 64, 345–350