José G. Miranda-Hernández

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.

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.

Synthesis and Characterization of Zn-Nix Advanced Alloys Prepared by Mechanical Milling and Sintering at Solid-State Process

Mechanical ball milling assisted by sintering in the solid state was used in this research to produce the Zn-Nix system alloy. The derivative powder compositions of Zn-Nix (x = 0, 5, 10, 15, and 20 wt.%) were obtained to study the Ni effects on the microstructural and mechanical properties. It is worth remarking that conventional methods are not appropriate for the manufacture of the Zn-Nix system alloy. The morphological structure and phases were examined by optical microscopy, X-ray diffraction, and SEM/EDS elemental mapping, whereas the mechanical behavior was accomplished by means of a diamond indentation print (Hardness Vickers). The results showed that the intermetallic γ-ZnNi phase did not form during milling time (<4 h); it appears after the sintering process, which is associated with atomic diffusion mechanism through grain boundary at the minimum interfacial energy (ΔG256°C = −13.83 kJ·mol−1). The powder Zn-Ni10 was found to have better properties. Semispherical coarser particles were seen into the metal matrix (Zn δ-hcp structure) as segregates; however, each particle contains an intermetallic compound Zn-Ni that encloses the Ni (α-fcc structure) pure phase. The Ni-α phase was then transformed into a γ-ZnNi intermetallic compound which shifts to higher values of mechanical hardness from about 60 HV to 400 HV units.

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.