S. Bueno et al. /Journal of the European Ceramic Sociery 25(2005)847-856 1 mm 40(A+T A40(A+ characteristic fracture surfaces of the laminates. The tensile surfaces are located at the lower part of th micrographs (a)AA10; (b)A10A40 behaviours of the composites due to the occurrence of microcracking at different levels. as discussed below Thermal expansion and dynamic Youngs modulus are the highest for alumina and the composite containing the low- Alumina est amount of aluminium titanate(Table 2). For alumina, AAl these values are in the range of those of dense and fine the 10(A+T) composite which, in principle, might be at tributed to the presence of Al2TiO5. In this way, the ma- terial AlO(A-+T) presented linear behaviour up to fracture, similar to monophase alumina, steeply stress drop and the lowest strains at fracture, as compared with the composites with higher Al TiOs contents(Fig 3a), in agreement with the smooth fracture surfaces of these samples(Fig. 4a). This fracture behaviour is characteristic of non-microcracked ma- terials. There are differences between alumina and 10(A+T) (a Strain [% Table 3 A10(A+T) Casting time and comparison between the obtained and calculated thick. ness for the layers A10A40 Casting Calculated Obtained time(s) thickness thickness A10A40 AlO(A+T)Layer I AlO(A+T)Layer 3 1200-1240 AlO(A+T)Layer 5 1449 2 Alumina-Layer 1 2200 AlO(A+T)Layer 2 91 300-330 1400-1500 Fig. 7. Characteristic nominal stress-apparent strain curves for AlO(A+T)Layer 4 149 310-335 compared to those for thick (25 mm x 5.5mm x 3.5mm) Alumina-Layer 5 105 2200 amples with the same compositions as those of the correspond layers (a)AA10 and alumina;(b)A10A40 and AlO(A+TS. Bueno et al. / Journal of the European Ceramic Society 25 (2005) 847–856 853 Fig. 6. Scanning electron micrographs of characteristic fracture surfaces of the laminates. The tensile surfaces are located at the lower part of the micrographs. (a) AA10; (b) A10A40. behaviours of the composites due to the occurrence of microcracking at different levels, as discussed below. Thermal expansion and dynamic Young’s modulus are the highest for alumina and the composite containing the low￾est amount of aluminium titanate (Table 2). For alumina, these values are in the range of those of dense and fine grained uncracked materials, and they are slightly lower in the 10(A+T) composite which, in principle, might be at￾tributed to the presence of Al2TiO5. In this way, the ma￾terial A10(A+T) presented linear behaviour up to fracture, similar to monophase alumina, steeply stress drop and the lowest strains at fracture, as compared with the composites with higher Al2TiO5 contents (Fig. 3a), in agreement with the smooth fracture surfaces of these samples (Fig. 4a). This fracture behaviour is characteristic of non-microcracked ma￾terials. There are differences between alumina and 10(A+T) Table 3 Casting time and comparison between the obtained and calculated thick￾ness for the layers Casting time (s) Calculated thickness (
m) Obtained thickness (
m) A10A40 A10(A+T)—Layer 1 313 2200 – A40(A+T)—Layer 2 70 300 360–390 A10(A+T)—Layer 3 481 1200 1200–1240 A40(A+T)—Layer 4 115 300 390–420 A10(A+T)—Layer 5 1449 2200 – AA10 Alumina—Layer 1 639 2200 – A10(A+T)—Layer 2 91 300 300–330 Alumina—Layer 3 996 1200 1400–1500 A10(A+T)—Layer 4 149 300 310–335 Alumina—Layer 5 3005 2200 – Fig. 7. Characteristic nominal stress–apparent strain curves for laminates compared to those for thick (25 mm × 5.5 mm × 3.5 mm) monolith samples with the same compositions as those of the corresponding external layers. (a) AA10 and alumina; (b) A10A40 and A10(A+T)