Examinando por Autor "de-Portu, Goffredo"
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Ítem 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 Processing of alumina-coated tetragonal zirconia materials and their response to sliding wear(Elsevier, 2010) Bueno, Salvador; Ferrari, Begoña; Melandri, Cesare; de-Portu, Goffredo; Baudín, CarmenAlumina-coated tetragonal zirconia stabilised with 3 mol% of Y2O3 (YTZP) specimens (30 mm × 30 mm × 6 mm) have been obtained by dipping of pre-sintered YTZP compacts in alumina suspensions and subsequent sintering. The coated specimens present hardness values and a wear resistance similar to those of reference dense alumina specimens and significantly higher than those of the YTZP substrates. The optimisation of the processing parameters is described. First, YTZP compacts with different open porosity levels were fabricated by colloidal filtration and subsequent thermal treatment at temperatures ranging from 1100 to 1400 °C. Coated compacts were obtained by dipping the porous ones in alumina suspensions prepared in ethanol with two different solid loadings: 3 and 10 vol.%, during immersion times up to 40 min. Sintering (1500 °C–2 h) of the coated compacts was performed and microstructural analysis allowed the selection of the optimum porosity levels for the YTZP substrates and dipping conditions. For the optimised conditions, YTZP plates (30 mm × 30 mm × 6 mm) were coated and the thermal treatment to reach densification of the substrate and the coating was optimised. Relatively thick coatings (≅200 μm) were obtained. Hardness and wear resistance were evaluated for sintered monolithic and coated YTZP compacts and an alumina reference material and the wear damage of the tested specimens was analysed.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.