V. Gallegos-Orozco

Electronic Structure of YFe2 by EELS and Ab Initio Calculations

The dielectric properties of the intermetallic cubic Laves phase compound YFe2 were determined by analyzing the low loss region of the EELS spectrum in a transmission electron microscope. From these data, the optical joint density of states (OJDS) was obtained by Kramers-Kronig analysis. Since maxima observed in the OJDS spectra are assigned to interband transitions; these spectra can be interpreted on the basis of numerical calculations performed with the Wien2k code, using the Fully-Linearized-Augmented-Plane wave (FLAPW) method within the Local-Spin-Density Approximation. Comparison between experimental results and theory shows good agreement.

Recycled Al Reinforced with Oxide Nanoparticles Produced by Stir-Casting Method

Aluminum alloys reinforced with hard nanoparticles named Metal Matrix Nanocomposites (MMNCs) are very attractive in many applications in the industry, this kind of materials exhibit improved mechanical properties with relatively low contents of reinforcement. Automotive and aerospace industries are demanding these composites for critical applications taking into account their low density and high temperature resistance characteristics. MMNC’s are materials reinforced with hard particles (e.g. oxides and nitrides) with size ranging from 10 nm to 100 nm. In the present work, nanocomposites based aluminum with hard nanoparticles of TiO2 and CeO2 were fabricated by combining two techniques such as mechanical milling and the stir-casting method. Compared to other routes, melt stirring process has some important advantages, e.g., the wide selection of materials, better matrix– particle bonding, easier control of matrix structure, simple and inexpensive processing, flexibility and applicability to large quantity production and excellent productivity for nearnet shaped components [1,2]. Nanoparticles and metallic powders, in the weight ratio of Recycled Al/nanoparticles = 3, were separately milled using a Spex ball mill in uncontrolled atmosphere during 2h. The device and milling media used were made from hardened steel. The milling ball to powder weight ratio was set to 5:1. Consolidated samples were added into molten recycled Al using a resistance furnace equipped with a graphite stirring system. Each cylinder was hot extruded in a direct extrusion system at 550 °C. The specimens in both asmilled and as-sintered conditions were studied by scan electron microscopy (SEM) and atomic force microscopy (AFM). The SEM bright-field image (see Fig. 1a) shows the microstructure of the Al-TiO2 nanocomposite, the inset shows a close up image of the TiO2 nanoparticles dispersed into the recycled Al matrix; these particles are in the size range of about 80 to 100 nm. Fig. 1b shows the AFM topography image of the Al-TiO2 composite after the hot extrusion process, the image reveal a homogeneous crystallite size distribution of about 50 to 100 nm. The inset shows the profile of the crystallite. Fig. 2a shows the SEM bright-field image of the microstructure of the Al-CeO2 nanocomposite after the hot extrusion process; the image also shows the presence of some fiber-shaped CeAl intermetallic compound. In the inset is clearly observed the CeO2 nanoparticles dispersed into the recycled Al matrix. The Figure 1b shows the crystallite size distribution where most of these crystallites are below 100 nm in size. The presence of these hard nanoparticles dispersed into the recycled Al prevents by the pinning effect, the excessive increase of the crystallite during thermo-mechanical extrusion process. The combined effect of hard nanoparticles dispersion and the small crystallite size, improved the mechanical properties of the recycled Al matrix.

Effect on Microstructure and Hardness of A2024 Aluminum Alloy Doped Cerium Oxide Nanoparticle

1. Centro de Investigación en Materiales Avanzados (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes 120, 31109 Chihuahua, Chih., México. 2. Facultad de Ingeniería Mochis, Universidad Autónoma de Sinaloa, Prol. Ángel Flores y Fuente de Poseidón, S.N., 81223 Los Mochis, Sinaloa, México. 3. Universidad Tecnológica de Chihuahua Sur, Carr. Chihuahua a Aldama Km. 3.5, 31313 Chihuahua, Chih., México.

Zinc Doped SnO2 Electronic Structure Study by EELS

F.C. Vasquez, V. Gallegos-Orozco, C. Ornelas-Gutierrez, W. Antunez-Flores, A. Santos-Beltran and F. Paraguay-Delgado 1. Centro de Investigación en Materiales Avanzados, S.C. (CIMAV), Laboratorio Nacional de Nanotecnología, Miguel de Cervantes 120, Complejo Industrial Chihuahua, 31109 Chihuahua, Chih., México. 2. Universidad Tecnológica Junta de los Ríos, Departamento de Nanotecnología, Av. Independencia 5007, C.P. 31050, Chihuahua, Chihuahua, México.

Study of Al 2 O 3 Nanofibers Dispersed in Al Matrix by EELS and Calculations Ab Initio

The necessity for improving the mechanical properties of aluminum alloys has motivated the study of Al base composites [1]. Mechanical Alloying process is employed to produce hardened composites to introduce reinforcing particles; this process is able to produce several phases including supersaturated solid solutions, metastable phases, amorphous phases, as well as reinforced metal-particle composites [2]. Using techniques like Electron Energy Loss Spectroscopy (EELS) and Transmission Electron Microscopy, it is possible to characterize this kind of materials. Recently, very important advances have been achieved in the description of the crystalline solid electronic structure through numerical calculations. There is a great diversity of available codes for DFT calculations, among them are the CASTEP code (pseudopotentials) and WIEN2k code, two available commercial programs that offer the possibility of ELNES calculations. ELNES provides details of the atomic local environment, coordination, bond type and valence states. The ELNES calculation can be performed with an energy resolution much better than those obtained by experiment. In this work, Al2O3 nanofibers were synthesized using Al powders (99 % pure) and C as raw materials. A mixture of Al powders at 75 wt. % and C powder at 25 wt. % was used to produce the compound. The mixture was mechanically processed in a high energy mill (Spex) for 4h and the product was compacted at ~950 MPa of pressure. The consolidated samples were sintered for 2h at 550°C. The characterization was carried out by Transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS).

Microstructural Characterization in Al-C-Al2O3 Composites Produced by Mechanical Milling

Aluminum-graphite-copper (Al-C-Cu) novel micro-composites have been produced using the Mechanical Alloying process (MA). The mechanical properties of the obtained composites have been evaluated. Yield strength (σy) values reached in the composites are considerably higher than those reported for pure aluminum. There is a direct relationship between σy and final graphite content in the composite. σy values increase as the nominal C content increases as well. We found that the most important hardening element was the graphite. We found that the optimal ratio Cu/C correspond to 0.33% for different volume fractions of graphite and cooper. There is an apparent synergy effect in σy between Cu and C. Results of TEM analysis have shown the presence of alumina particles in fiber shape from oxide surface of powder. Presence of alumina fibers in the composite improves the mechanical properties.