Materials Science Forum Vols. 660-661

Abstract: This work have like object to research the metallic matrix, Ni-Sn and Co-Sn, and subsequent to add up to diamond for analyses the possibility the to replace the Co with Ni in the metallic matrix for to act like binder for subsequent use in cutting tools. The metallic powders and the composites were mixed and then hot pressed and processed at 35MPa/800°C/3 min. In these sintered samples, it was made hardness HRB, wear resistance test and scanning electron microscopy for to identify which one matrix owns better mechanical resistance and diamond adherence required for diamond cutting tools.

Abstract: A new integrated method for direct preparation of cermet materials is proposed consisting of a powder processing method allied to a special sintering step. The powder is obtained by mechanical alloying route where a specific morphologic design is searched to yield thin metal plated ceramic particles. These have the proper characteristics to engage the sintering by activated surface (SAS) consolidation method. The last is triggered by partial evaporation and reactive sintering of thin metal layers, therefore exposing high active surfaces with superior sinterability. Refractory sacrifice metal components are found to play an important role. The application of the integrated method to Ni-ZrO2 cermet with selected metal additives is investigated. Sintering temperatures can be reduced by more than 300°C for the same final density range. The resulted powders and pellets microstructures are analysed accordingly to the projected expected ones. The thermophysical and electrical properties measurements are performed for evaluate phases percolation.

Abstract: In most engineering fields there is increasing demand for materials with enhanced physical properties. Components of complex systems exposed to severe environments often require coatings for adequate thermal insulation and to prevent wear, erosion and/or oxidation. Coatings prepared with nanostructured material have, in general, exhibited higher hardness and strength compared to conventional coatings. This paper presents the microstructure, mechanical properties, thermal stability and erosion-oxidation resistance of HVOF (High Velocity Oxygen Fuel) sprayed coatings of Cr3C2-X(Ni20Cr) prepared using nanocrystalline and as-received (AR) powder as feedstock. Details about nanocrystalline powder synthesis and characterization are also presented.

Abstract: In recent years, scientific research showed an increasing interest in the field of nanotechnology, resulting in several techniques for the production of nanoparticles, such as methods of chemical synthesis. Among the various existing methods, the Pechini method has been used to obtain nanoparticles of titanium dioxide (TiO2). Thus, this work aims to synthesize and characterize nanoparticles of TiO2 obtained by this method. The technique constitutes in the reaction between citric acid with titanium isopropoxide, resulting as the product the titanium citrate. With the addition of the ethylene glycol polymerization occurs, resulting in a polymeric resin. At the end of the process, the resin is calcined to remove organic matter, creating nanoparticles of TiO2. The resulting powders were characterized by thermogravimetric analysis (TGA) and thermal differential analysis (DTA), X-ray diffraction, absorption spectrophotometry in the infrared, method of adsorption nitrogen / helium (BET method) and scanning electron microscopy. The results obtained in the characterization techniques showed that the Pechini method is promising in obtaining nanosized TiO2.

Abstract: Power metallurgy has been used to produce compacts by two different routes. In this work, porous three-dimensional (3-D) substrates were prepared by the conventional pre-forms sintering method. Titanium powders were uniaxial pressed at 110 Mpa and vacuum (1 x 10-5 Pa) sintered at 1500 K. Another group of substrates were obtained by the space holder technique. Irregular shaped carbamide particles (210 – 250 m diameters) were mixed to Ti powders, pressed and sintered. Before the sintering the compacts were heated at 470 K for 3 h to eliminate the spacing holder agent. Nanodiamond films were grown by hot-filament chemical vapor deposition technique on such substrates at 870 K from a mixture of Ar/H2 (80%-18,5%) respectively and a solid carbon source. SEM images show the substrates totally covered by a nanodiamond film including deeper planes. Raman Spectra confirm the good quality of the nanodiamond film.

Abstract: From studies on the Damascus steel, the manufacturing of ultra-high carbon content steel (UHCS) by powder metallurgy has been carried out in previous works. UHCSs have been manufactured mixing iron and graphite powders, uniaxial compacting, and sintering in vacuum atmosphere. Finally, they have been hot-rolled at relatively low temperatures using their superplasticity to obtain optimum properties. High hardness particles of SiC (micro and nanometric size) and diamond (with and without coating) were added to UHCS to produce inserts for cutting discs. Their mechanical properties have been studied through bending tests and hardness measurements. SEM observations have shown how the structure of the steel and the particles has been modified depending on the performed thermo-mechanical treatment. This way, it is possible to justify the effect of the addition of high hardness particles in the reduction of plasticity and wear resistance of the material.

Abstract: Beta titanium alloys parts are used on advanced aerospace systems because of their high strength to weight ratio and excellent corrosion resistance. Production of powder metallurgy titanium alloys components may lead to a substantial reduction in the cost, compared to those produced by conventional cast and wrought processes, because additional working operations and material waste can be avoided. In this work, beta Ti-45Nb and Ti-50Nb were produced by the blended elemental technique, followed by uniaxial and cold isostatic pressing with subsequent densification by sintering. Sintered samples were characterized for phase composition by XRD, microstructure by SEM, hardness by Vickers indentation, specific mass by the Archimedes method and elastic modulus by resonance ultrasound. The sintered samples presented only the beta phase, higher hardness and lower elastic modulus when compared to Ti6Al4V alloy and experimental specific mass value near theoretical specific mass. These characteristics are adequate for application on several aerospace parts.

Abstract: This work has as objective the study experimental and computational of the hydrodynamics of gas-solid fluidized bed. The gas-solid fluidized beds present important applications in chemical industry; among typical examples of fluidized beds some applications could be outlined: the syntheses and catalytic reactions, the catalytic regeneration, the combustion and gasification of coal, coating, drying, etc. The simulated data were obtained through the commercial CFD (Computational fluid dynamics), and the results were compared to those obtained by experiments conducted in a fluidized bed, containing jambu seeds (Sphilantes oleracea L.) of 772.21  2.98 μm in diameter, sphericity de 0.45  0.0066, bulk density 1130.8 ± 0.22 Kg/m3 and with porosity 0.2303  0.0099. In this work the porosity profile and characteristic curve of fluidized bed were calculated by using an Eulerian multiphase model. The comparisons showed a very good agreement between experimental and simulation results.

Abstract: The coating of vegetable seeds is a very common technique, mainly for the species which have small seeds. One of its functions is to increase the seed size to direct sowing. In the present study the coating of Spilanthes oleracea L. seeds with a polymeric suspension in fluidized bed was analyzed. The effects of process variables on the coating efficiency of top-spray fluidized bed coating were evaluated. The independent variables studied were the flow rate of coating suspension and the air mass flow. The quantification for the entrance variables influence on the coating efficiency and granule growth, as well as the identification of optimal conditions were made by means of an experiment factorial design technique. Polynomial models for the responses: efficiency and relative growth of the particles were deduced. The highest coating efficiency was achieved at a high flow rate of coating suspension.

Abstract: This work was observed the phase formations of the mixture Al-Cu-Fe processed vial mechanical alloying, powders pressing at room temperature and subsequent heat treatment. The mixture of powders was made on the nominal composition Al65Cu20Fe15. A mill of high energy of the horizontal atrittor type was used to process the powders mixtures, in fixed time of two hours of milling. After milling, the powders were pressing in a die closed, with a diameter of about 28mm. The samples were observed by optical microscopy and analyzed X-ray diffractometry. The results obtained in this study provide a basis for setting parameters may be used as a basis for future research and possible applications.