Materials Science Forum Vols. 660-661

Abstract: Ti-35Nb-7Zr-5Ta alloy is considered an attractive material for implants manufacture due to an excellent combination of properties, including high mechanical and corrosion resistance, beyond the lowest elastic modulus among the titanium alloys. The alloy processing by powder metallurgy (P/M) eases the obtainment of parts with near-net shape forming and low production costs. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 800-1600 °C, in vacuum. The isochronal sintering demonstrated to be efficient for the study of the microstructural evolution. The samples presented high densification and adequate microstructure. The results show that a beta-homogeneous microstructure is obtained in the whole sample extension when sintered at high temperatures beyond that P/M technology allows an effective porosity control.

Abstract: It is important to control the martensitic transformation start temperature (Ms) of Ti–Ni alloys because it determines the temperature range over which the shape memory effect and superelasticity appear. Powder metallurgy (PM) is known to provide the possibility of material-saving and automated fabrication of at least semi-finished products as well as net-shape components for NiTi alloys. In this study powder with different particle sizes was subjected by gas atomization. The evolution of the control the martensitic transformation start temperature (Ms) was studied by differential scanning calorimetry. The effect of the particle size of powders on the transformation temperatures behaviors was discussed.

Abstract: The preparation of negative electrodes for nickel-metal hydride (Ni-MH) batteries using a La0.7Mg0.3Al0.3Mn0.4Co0.5Ni3.8 alloy in the as-cast state has been carried out. The alloy was mechanically crushed (<44 m) and a battery was manufactured with this material. The mean discharge capacity achieved using this method was 384 mAh/g. Another two batteries were prepared using a hydrogen powdered La0.7Mg0.3Al0.3Mn0.4Co0.5Ni3.8 alloy at low and high pressures (2-10 bar). It has been shown that hydrogen powdering facilitates the activation of the negative electrode for Ni-MH batteries. This study also included the characterization of the hydrogenated and crushed powders. These materials were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD).

Abstract: A nickel-metal hydride (Ni-MH) rechargeable battery has been prepared using a La0.7Mg0.3Al0.3Mn0.4Co0.5Ni3.8 alloy as the negative electrode. The maximum discharge capacity of the La0.7Mg0.3Al0.3Mn0.4Co0.5Ni3.8 alloy has been determined (350 mAh/g). Using a high starting charging rate (2857 mAg-1) an efficiency of 49% has been achieved in the 4th cycle. The alloy and powders have been characterized by scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and X-ray diffraction (XRD).

Abstract: The crystallographic alignment of various permanent magnets has been investigated by X-ray pole figure analysis. Attempts have been made to measure the degree of alignment of these sintered magnets using the (105) reflection. It has been shown that the (105) pole figure can be used only to verify small differences in texture in magnets high degree of crystallographic alignment. A comparison between the measured and the calculated L105 index showed good agreement.

Abstract: Nanometric powders of WC with 10 weight% Co were mixed in high-energy mill. Compaction was performed at 200MPa and processed by the technique of high pressure and high temperature (HPHT). Sintering conditions were P = 5GPa, T = 1300-1400-1500° C, t = 2-4 min. For comparative purposes, samples were conventionally sintered at T = 1400° C, t = 45 min, vacuum of 10-2 mbar.

Abstract: Alfa/beta titanium alloys have been intensely used for aerospace and biomedical applications. Production of powder metallurgy titanium alloys components may lead to a reduction in the cost of parts, compared to those produced by conventional cast and wrought (ingot metallurgy) processes, because additional working operations (machining, turning, milling, etc.) and material waste can be avoided. In this work, samples of Ti- 10, 15Nb (weight%) alloys were obtained by the blended elemental technique using hydride-dehydride (HDH) powders as raw material, followed by uniaxial and cold isostatic pressing with subsequent densification by sintering carried out in the range 900–1500 °C. These alloys were characterized by X-ray diffractometry for phase composition, scanning electron microscopy for microstructure, Vickers indentation for hardness, Archimedes method for specific mass and resonance ultrasound device for elastic modulus. For the samples sintered at 1500°C it was identified  and  phases. It was observed the influence of the sintering temperatures on the final microstructure. With increasing sintering temperature, microstructure homogenization of the alloy takes place and at 1500 °C this process is complete. The same behavior is observed for densification. Comparing to the Ti6Al4V alloy properties, these alloys hardness (sintered at 1500 °C) are near and elastic modulus are 18% less.

Abstract: In recent years, many computational fluid dynamics (CFD) studies have appeared attempting to predict cyclone pressure drop and collection efficiency. While these studies have been able to predict pressure drop well, they have been only moderately successful in predicting collection efficiency. Part of the reason for this failure has been attributed to the relatively simple wall boundary conditions implemented in the commercially available CFD software, which are not capable of accurately describing the complex particle-wall interaction present in a cyclone. According, researches have proposed a number of different boundary conditions in order to improve the model performance. This work implemented the critical velocity boundary condition through a user defined function (UDF) in the Fluent software and compared its predictions both with experimental data and with the predictions obtained when using Fluent’s built-in boundary conditions. Experimental data was obtained from eight laboratory scale cyclones with varying geometric ratios. The CFD simulations were made using the software Fluent 6.3.26.

Abstract: Ceramic materials have properties defined by their chemical and micro-structural composition. The quantification of the crystalline phases is a fundamental stage in the determination of the structure, properties and applications of a ceramic material. Within this context, this study aims is the quantitative determination of the crystalline phases of the ceramic materials developed with addition of mineral coal bottom ash, utilizing the X ray diffraction technique, through the method proposed by Rietveld. For the formulation of the ceramic mixtures a {3,3} simplex-lattice design was used, giving ten formulations of three components (two different types of clays and coal bottom ash). The crystalline phases identified in the ceramic materials after sintering at 1150oC during two hours are: quartz, tridimite, mullite and hematite. The proposed methodology utilizing the Rietveld method for the quantification relating to crystalline phases of the materials was shown to be adequate and efficient.

Abstract: The effect of three different sintering additive systems on densification of boron carbide powder was investigated. The sintering additives were Al2O3:Y2O3, AlN:Y2O3 and BN:Y2O3 compositions. Powder mixtures were prepared with 10 vol% of sintering aids following conventional powder technology processes. Samples were sintered by pressureless sintering at 2050 °C/30min in argon atmosphere. Sintered samples were compared to a sintered B4C without sintering additive. Samples were characterized by XRD to analyze the crystalline phases after sintering and SEM to observe the microstructure and the second phase distribution. YB4 and YB2C2 were identified in all samples, indicating a reaction between Y2O3, B4C and B2O3 present at the B4C particle surface. The best densification result was achieved with Al2O3:Y2O3 additive system, showing 92.0 % of theoretical density, low porosity and 15.2 % of linear shrinkage. But this sample showed the highest weight loss.