Navegando por Autor "Vieira, F. A."
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Artigo Effect of Y2O3 addition on the densification and mechanical properties of alumina±niobium carbide composites(Elsevier, 2000-04-21) Acchar, Wilson; Greil, P.; Martinelli, Antonio Eduardo; Vieira, F. A.; Bressiani, A. H. A.; Bressiani, José CarlosAlumina-based composites reinforced with refractory carbides are potential cutting tool materials. They exceed the capabilities of cemented carbides with respect to hot hardness and thermal stability, resulting in faster cutting speeds. Liquid-phase sintering of Al2O3±NbC composites was investigated as an alternative to pressure-assisted processes. Al2O3 reinforced by NbC (5±40 wt.%) was sintered with 3 wt.% Y2O3. In order to assess the e ect of the formation of a liquid phase on the properties of the composites, sintering was carried out either below or above the Al2O3±Y2O3 eutectic temperature, at 1650 and 1800 C, respectively. Density, hardness, fracture toughness and wear resistance of the composite materials were evaluated. Liquid phase sintering did not affect the fracture toughness, but improved both the density and the hardness of the material, regardless of its NbC contents. Higher concentrations of NbC increased the wear resistance of the compositeArtigo Sintering behaviour of alumina–tungsten carbide composites(Elsevier, 2000-05-31) Acchar, Wilson; Martinelli, Antonio Eduardo; Vieira, F. A.; Cairo, Carlos Alberto AlvesAlumina reinforced with tungsten carbide has been investigated as an alternative material for metalworking, combining resistance to high service temperatures and improved toughness. Pressureless sintered and hot-pressed Al2O3–WC composites were manufactured and characterised. The use of Y2O3 as a sintering additive has also been evaluated. Additions of up to 30 wt.% WC resulted in limited grain boundary pinning and corresponding high densification. Although the addition of Y2O3 improved sintering, the presence of a residual grain boundary phase (YAG) was harmful to the fracture toughness of the composites, as it affected the effectiveness of the crack deflection mechanism that takes place at the interfaces between Al2O3 and WC grains. Hot-pressing resulted in hardness ∼17.5 GPa and fracture toughness ∼7 MPa m−1/2, which is an improvement compared to alumina reinforced by other refractory carbides