S. Bueno et al. /Journal of the European Ceramic Sociery 28(2008)1961-1971 1965 3 0100020003000400050006000 Energy (ev C 1000200030 400050006000 100nm 95 Fig. 2. Characteristic scanning transmission electron microscopy(STEM)observations for the A10 composites sintered at 1550C together with EDX chemical nalysis(au -arbitrary units). (a) Alumina and aluminium titanate grains. No Ti was detected inside the alumina grains (b)Chemical profile along a line traversing an alumina/alumina grain boundary showing enrichment in Ti Negligible Si contents are detected. lar to those of the monophase specimens. However, the eDx should be aluminium titanate, formed by reaction of the thermo- line profiles across alumina grain boundaries in the composites dynamically incompatible compounds alumina and titania. The (Fig. 2b) showed a systematic evidence of Ti segregation at the fact that such particles were not observed by STEM should be alumina/alumina grain boundaries. Values from 0.5 to 2.5 Ti due to the relatively small portions of material characterized by wt% were detected with no systematic variation with alumina this method(two samples were observed) graIn size. The presence of the major impurity in the starting pow- 4.2. Toughness parameters ders, Si, was also investigated and only no Si or negligible Si contents were found in the grain boundaries(Fig. 2b). More- The load-displacement curves for both composites and for over, STEM-EDX analysis evidenced diffusion of titanium ions the three relative notch sizes showed stable fracture In Fig. 3 across the alumina grain boundaries during sintering. Thus, the characteristic curves for specimens with a relative notch length composition of the nanosized particles found by SEM(Fig. 1b) a/W=0.5 are shown. Controlled fracture was difficult to achieveS. Bueno et al. / Journal of the European Ceramic Society 28 (2008) 1961–1971 1965 Fig. 2. Characteristic scanning transmission electron microscopy (STEM) observations for the A10 composites sintered at 1550 ◦C together with EDX chemical analysis (a.u. = arbitrary units). (a) Alumina and aluminium titanate grains. No Ti was detected inside the alumina grains. (b) Chemical profile along a line traversing an alumina/alumina grain boundary showing enrichment in Ti. Negligible Si contents are detected. lar to those of the monophase specimens. However, the EDX line profiles across alumina grain boundaries in the composites (Fig. 2b) showed a systematic evidence of Ti segregation at the alumina/alumina grain boundaries. Values from 0.5 to 2.5 Ti wt.% were detected with no systematic variation with alumina grain size. The presence of the major impurity in the starting pow￾ders, Si, was also investigated and only no Si or negligible Si contents were found in the grain boundaries (Fig. 2b). More￾over, STEM–EDX analysis evidenced diffusion of titanium ions across the alumina grain boundaries during sintering. Thus, the composition of the nanosized particles found by SEM (Fig. 1b) should be aluminium titanate, formed by reaction of the thermo￾dynamically incompatible compounds alumina and titania. The fact that such particles were not observed by STEM should be due to the relatively small portions of material characterized by this method (two samples were observed). 4.2. Toughness parameters The load–displacement curves for both composites and for the three relative notch sizes showed stable fracture. In Fig. 3 characteristic curves for specimens with a relative notch length a/W = 0.5 are shown. Controlled fracture was difficult to achieve