Enrique Rocha-Rangel

Alumina-Copper Composites with High Fracture Toughness and Low Electrical Resistance

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.

Microstructure of alumina-matrix composites reinforced with nanometric titanium and titanium carbide dispersions

-titanium powders which were thoroughly mixed under high energy ball-milling and through the second step it was induced the formation of titanium carbide during different times at 500 °C by the cementation packing process. SEM and EDS analysis of the microstructures obtained in both sintered and cemented bodies were performed in order to know the effect of the activated carbon used as cementing agent on the titanium for each studied composite. It was observed that a titanium carbide layer growth from the surface into the bulk and reaches different depth as the titanium content in the composites increases. On the other hand, the use of ductile titanium notably enhanced density level and fracture toughness of the composites.

Effect of Nickel Addition on Microstructure and Mechanical Properties of Aluminum-Based Alloys

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.

Direct Extrusion Production of Monolithic Ceramics with Different Cross Section

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.

Study of the electrophoretic deposition copper–carbon nanotubes composite coatings in deep eutectic solvent using a Taguchi experimental design approach

ABSTRACT The present work discusses the electrophoretic deposition (EPD) of copper–carbon nanotubes (Cu–CNTs) composite coatings in a Deep Eutectic Solvent (DES) media, using a non-symmetric deposition process. A Taguchi experimental design is implemented in order to assess the effect of the different parameters on the microstructural characteristics of the coatings. The analysis of the design of experiments (DOE) is performed with the signal to noise (S/N) ratio and the analysis of variance. The results clearly reveal that the time of deposition is the most influential parameter on crystallite size, whereas the asymmetric factor has the highest effect on the preferential deposition of Cu or C and thus on the chemical composition. It is therefore concluded that by changing some of the parameters, EPD can be implemented to develop nanostructured composite coating having a desired crystallite size and morphology.

Effect of silver nanoparticles on the microstructure and mechanical properties of alumina ceramics

ABSTRACT In this work, the effect of additions of silver nanoparticles on the microstructure and mechanical properties of alumina-based ceramic was studied. The processing method for the manufacturing of alumina/silver composites imply high energy mechanical milling in a planetary type mill, cold uniaxial compaction and pressureless sintering in an inert atmosphere at 1500°C for 2 h. From the results after the milling step, approximately 45% of the powders have a particle size less than 1 μm. The microstructure observed by SEM is very fine and homogenous; the presence of silver apparently inhibits the grain growth of the alumina. With respect to mechanical properties, increases of the silver content in the matrix causes decrease of Young’s modulus and flexural strength of the composite obtained in 1.5 and 4.6%, respectively. On the other hand, the presence of silver greatly enhances the fracture toughness of alumina, from an increase of 4.2 MPa m−0.5 for monolithic alumina to 10 MPa m−0.5 for alumina with silver additions of 2 wt- %, representing an improvement of 138% in toughness of alumina. Lastly, hardness for this same sample was incremented in 12%.

Synthesis of Al2O3/Ti/TiN Functional Graded Materials by Means of Nitriding in Salts of Al2O3/Ti Composites

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.

Titanium Effect on Microstructure and Fracture toughness of Al2O3-BASED Composites

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.

Alumina-Based Functional Materials Hardened with Al or Ti and Al-nitride or Ti-nitride Dispersions

The synthesis of Al 2 O 3 -based functional materials having 10 vol. % of fine aluminum or titanium and aluminum-disperse or titanium-dispersed nitride hardened-particles has been explored. Two experimental steps have been set for the synthesis; specifically, sintering of Al 2 O 3 -aluminum or Al 2 O 3 -titanium powders which were thoroughly mixed under high energy ball-milling, pressureless-sintered at 1400°C during 1 h in argon atmosphere and then for the second step it was induced formation of aluminum nitride or titanium nitride at 500°C during different times (24, 72 and 120 h) by a nitriding process via immersion in ammoniac salts. SEM analyses of the microstructures obtained in nitride bodies were performed in order to know the effect of the ammoniac salts used as nitrating on the microstructure of aluminum or titanium for each studied functional material. It was observed that an aluminum nitride or titanium nitride layer growth from the surface into the bulk and reaches different depth as the nitriding time of the functional material was increased. The use of aluminum or titanium significantly enhanced density level and hardness of the functional materials.

Synthesis of Al2O3-Ni3Al Cermets by Room-Temperature Ball Milling of Al, Ni and Al2O3 Mixtures

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.