Papers by Author: Enrique Rocha-Rangel

Abstract: The synthesis of Al₂O₃/Ti/TiN functional graded material (FGM) through the nitriding in salts of previously Al₂O₃-10 vol. % Ti fabricated composites was studied. The matrix for the preparation of the FGM is formulated of an Al₂O₃-based composite that presents a homogeneous dispersion of very fine metallic titanium particles. After nitriding process, microstructural observations were carry out on the transversal zone of the materials’ surface showing the presence of a very thin film of about 37 µm of a constituent that was identified as TiN. Micro-hardness measurements performed from the surface to the core of the FGM confirm an increment on the hardness near the material’s surface.

Abstract: The effect of different titanium additions (0.5, 1, 2, 3 and 10 vol. %), milling intensity (4 and 8 h) and sintered temperature (1500 and 1600 °C) on microstructure and fracture toughness of Al₂O₃-based composites was analyzed in this study. After high energy milling of a titanium and Al₂O₃ mixtures, powder mixture presents fine distribution and good homogenization between ceramic and metal. After milling powders during 8 h they were obtained very fine particles with 200 nm average sizes. Microstructures of the sintered bodies were analyzed with a scanning electron microscopy, where it was observed that the microstructure presents the formation of a small and fine metallic net inside the ceramic matrix. From fracture toughness measurements realized by the fracture indentation method, it had that when titanium content in the composite increases, fracture toughness is enhanced until 83% with respect to the fracture toughness of pure Al₂O₃. This behavior is due to the formation of metallic bridges by titanium in the Al₂O₃ matrix.

Abstract: In this work a comparative study between microstructure and mechanical properties of aluminum-nickel alloys with different contents of nickel was carried out. Alloys were produced by powders metallurgy. Characterization results indicates that the microstructure of the aluminum-nickel alloys present a thin and homogeneous distribution of an intermetallic compound in the aluminum’s matrix, identified as Al₃Ni. Furthermore, it was find out that the amount of intermetallic Al₃Ni increase as the nickel content in the alloy rises. Regarding the mechanical properties evaluated; it was establishes that the hardness, compression and flexion resistances also were improved due to the presence of the intermetallic compound.

Abstract: Through an intense mixing process of Al2O3 powder with different copper contents, Al2O3-Cu composites were fabricated by sintered at 1300°C during 1h, where the likely liquid sintering mechanism, lead to obtain composites with relative densities greater than 95%. Scanning electron microscopy was used to observe the resulting microstructures, which indicated that these composites were mostly formed by a fine and homogeneous Al2O3-ceramic matrix with immerse nano-metallic copper particles. The behavior of both fracture toughness and electrical resistance of the composites is directly dependent with the copper content in the matrix. As the copper contents increased, the composites exhibited high values of fracture toughness, whereas, their electrical resistance is reduced considerably.

Abstract: The present work describes the fabrication of monolithic ceramics of different geometries through direct extrusion of ceramic pastes. Using this technique, ceramic rods with triangular, hexagonal, honey-like and tubular cross sections have been produced. The shape of some of these monolithic materials allows piling them up for building big catalytic reactors. After extruding and sintering, all processed ceramics have appropriate characteristics such as homogeneous texture, and controlled density and porosity. These results suggest the feasibility of using the extruded ceramics for different catalysis and filtering applications. Some features of the monolithic ceramics and the fabrication process will be analyzed.

Abstract: The synthesis of Al2O3-Ni3Al cermets with interpenetrating networks has been performed via a pressureless reactive sintering process. The synthesis has been induced by means of a solidstate reaction of Al + Ni + Al2O3 powders under intensive ball milling. The mixtures have been heat treated in an inert atmosphere (N2) in order to control the exothermic reaction between Ni and Al, with special care at temperatures near the melting point of Al. Dense and homogeneous microstructures have been obtained, composed by a matrix of Al2O3 reinforced with a Ni3Al intermetallic. Thermodynamic calculations indicate that such a cermet can be fabricated by in situ reaction synthesis. This suggests that a pressureless reaction sintering process may be a general route to synthesizing cermets with the prospect for the production of cermets with interpenetrating networks.