Departamento de Ingeniería Química, Ambiental y de los Materiales
URI permanente para esta comunidadhttps://hdl.handle.net/10953/42
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Examinando Departamento de Ingeniería Química, Ambiental y de los Materiales por Materia "Al2TiO5"
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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; M. Helene, Berger; Moreno, RodrigoÍtem Improved wear behaviour of alumina-aluminium titanate laminates with low residual stresses and large grained interfaces(Elsevier, 2011) Bueno, Salvador; Micele, Lorenzo; Melandri, Cesare; Baudín, Carmen; de-Portu, GoffredoThe wear behaviour of a monolithic alumina and an alumina–aluminium titanate laminated structure was studied. The laminate, containing surface fine grained alumina layers and internal composite layers with 10 vol.% of aluminium titanate, showed relatively low (∼=20 MPa) compressive residual stresses at the surface. Interfaces between layers were constituted by large alumina grains (up to =50 m) that promoted toughening due to crack deflection and branching. Wear tests were performed on square specimens (30 mm × 30 mm × 6 mm) using the pin-on-disc method. The laminates showed higher wear resistance than the monolithic alumina. The analysis of the results together with SEM-EDX observations was performed to identify possible wear mechanisms. The wear resistance improvements are discussed in terms of the residual stresses in the laminate and the properties provided by the special microstructure of the interfaces.Ítem Layered materials with high strength and flaw tolerance based on alumina and aluminium titanate(Elsevier, 2007) Bueno, Salvador; Baudín, CarmenLaminates in which high strength external layers and flaw tolerant internal layers with similar compositions are combined, can provide improved mechanical behavior in relation to that of monolithic materials with the same composition as the layers. The limitation of this design, in which no residual stresses are present, is the difficulty that involves the co-sintering of layers with large microstructural differences in the green state. This work describes a new method to obtain laminates constituted by layers with large differences in terms of grain size starting from green bodies with similar microstructures. The approach is based on the effect of small amounts of titania as agents for alumina grain growth enhancement. Starting from fine grained green bodies that combined alumina layers with composite layers made of mixtures of alumina and titania, additional "in situ" formed layers constituted by large (≅20-30µm) alumina grains were found after sintering contiguous to the composite layers. The thickness of the "in situ" formed layers reached up to 200 µm, depending on the thermal treatment (1450-1550ºC). The fracture behaviour of the laminates and the monoliths was studied, using stable SEVNB (Single Edge V Notched Beam) tests, in terms of work of fracture and the critical stress intensity factor in mode I, KIC. The large grain sized alumina layers reinforced the laminates by crack branching and bridging.Ítem Non-destructive characterization of alumina/aluminium titanate composites using a micromechanical model and ultrasonic determinations. Part I. Evaluation of the effective elastic constants of aluminium titanate.(Elsevier, 2008) Bueno, Salvador; González-Hernández, Margarita; Sánchez-Martín, Teresa; Anaya-Velayos, José Javier; Baudín, CarmenA method to evaluate the elastic constants of aluminium titanate in alumina/aluminium titanate composites is described. Results are derived from a three-phase micromechanical model proposed to relate the velocity of propagation of ultrasounds in the materials with their microstructural characteristics and the elastic behaviour of the constituents. Dense and un-cracked alumina and alumina + 10 vol.% aluminium titanate specimens have been fabricated by colloidal processing and the longitudinal and transverse ultrasound velocities have been determined by the ultrasonic jointly pulse-echo and transmission ultrasound immersion techniques, employing a digital signal processing. In order to assure the adequacy of the proposed method, results for monophase alumina have been compared to those obtained from the resonance frequencies of high density alumina plates tested in flexure and shear. The values of elastic moduli obtained using the two methods were coincident, which assured the validity of the non destructive proposed method.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.Ítem Reduced strength degradation of alumina-aluminium titanate composite subjected to low-velocity impact loading(Elsevier, 2008) Bueno, Salvador; Micele, Lorenzo; Baudín, Carmen; de-Portu, GoffredoThe impact behaviour of monophase alumina and alumina-aluminium titanate monolithic composite ceramics that present flaw tolerant behaviour was studied. Low-velocity impact loading tests were performed on bending bars and the residual strength after the impact was evaluated by 4-point bending tests. The impact tests were monitored using an instrumented drop-weight machine. During impact, the composites absorbed higher energy than the monophase material. The strength retention, in percentage, after the impact was significantly higher for the composite that presented damage tolerance for impact energy levels higher than monophase alumina. These results are discussed and fractographic analysis was used to identify the mechanisms responsible for the lower strength degradation of the composite.