Examinando por Autor "Moreno-Botella, Rodrigo"
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Ítem Design and processing of Al2O3–Al2TiO5 layered structures(Elsevier, 2005) Bueno, Salvador; Moreno-Botella, Rodrigo; Baudín, CarmenAl2O3-Al2TiO5 layered composites were manufactured by a colloidal route from aqueous Al2O3 and TiO2 suspensions with 50vol.% solids. The mechanical behaviours of individual monolithic composite materials were combined and taken as basis for the design of the layered structures. Residual stresses which are likely to occur due to processing and thermally introduced misfits were calculated and considered for the manufacture of the laminates. Monoliths with 10, 30 and 40 vol.% of second phase showed that increasing proportions of aluminium titanate decrease strength and increase the non-linear behaviour. In order to obtain the desired combination of mechanical behaviours of the layers, two laminate designs with external and central layers of one composition and the alternating internal layer of the other composition were chosen taking into account chemical compatibility and development of residual stresses. In the system AA10, external and central layers of monophase Al2O3 with high strength were combined with intermediate layers of Al2O3 with 10vol.% of Al2TiO5. The system A10A40 was selected to combine low strength and energy absorbing intermediate layers of Al2O3 with 40vol.% of Al2TiO5 and sufficient strength provided by external layers of Al2O3 with 10vol.% of Al2TiO5. The stress-strain behaviour of the laminates was linear up to their failure stresses, with apparent strain for zero load after fracture larger than that corresponding the monoliths of the same composition as that of the external layers. Moreover, the stress drop of the laminate samples occurred in step-like form thus suggesting the occurrence of additional energy consuming processes during fracture.Ítem Fracture behaviour of microcrack-free alumina-aluminium titanate ceramics with second phase nanoparticles at alumina grain boundaries(Elsevier, 2008) Bueno, Salvador; Berger, Marie Hélène; Moreno-Botella, RodrigoAlumina + 10 vol.% aluminium titanate composites were obtained by colloidal filtration and reaction sintering of alumina and titania. The materials were dense with aluminium titanate grains of average sizes 2.2–2.4 μm located mainly at alumina triple points. The reaction sintering schedule promoted the formation of additional nanometric grains, identified as aluminium titanate using STEM–EDX analysis between the alumina grains. This special microstructure led to a change of the toughening mechanism from the typical crack bridging reported for microcrack-free composites fabricated from alumina and aluminium titanate powders to microcracking. The identification of microcracking as the main toughening mechanism was done from the analysis of stable fracture tests of SENVB samples in three points bending and fractographic observations. Monophase alumina materials with similar grain sizes were used as reference. Different fracture toughness parameters were derived from the load–displacement curves: the critical stress intensity factor, KIC, the critical energy release rate, GIC, the J-Integral and the work of fracture, γWOF, and the R curves were also built. The comparison between the linear elastic fracture parameters and the non-linear ones revealed significant toughening and flaw tolerance.Ítem Reaction sintered Al2O3/Al2TiO5 microcrack-free composites obtained by colloidal filtration(Elsevier, 2004) Bueno, Salvador; Moreno-Botella, Rodrigo; Baudín, CarmenDense and microcrack-free Al2O3 / Al2TiO5 composites (10, 30 and 40 vol. % of Al2TiO5) have been obtained by colloidal filtration and reaction sintering, using alumina and titania as starting powders. The processing of the composites has been studied focusing on the rheological behaviour of aqueous suspensions of each powder and of mixtures. Colloidal filtration of optimised suspensions, with a solid loading as high as 50 vol. %, and a thermal treatment at 1450ºC, lead to completely reacted and uncracked sintered materials with homogeneously distributed aluminium titanate contents up to 40 vol. % and high density. Thermal diffusivity values from 25 to 800ºC are coincident on heating and cooling for the three studied composites, and decrease with temperature and with aluminium titanate content.