Metallic powder injection molding using low pressure

The demand by high performance materials that have to support severe service conditions at a reasonable cost has been forcing the powder metallurgy to improve constantly. The most recent and more important innovation in the area is the process of powder injection.Powder injection molding (PIM) is a technology capable of producing a new range of components from powders. This advanced technology overcomes the existent limitations in the forming of products with complex geometry. The process presents countless variations which are used in the industry today. Invariably, it consists of mixing the powders and a thermo-plastic binder, injecting the mass in the mold in the wanted form, debinding, sintering and making optional secondary operations, as for example, machinery.The purpose of this work is to review the metal injection molding techniques and apply the low pressure injection molding process to family of parts using metallic powder with 10 mum particle size. This work also comments the design and construction of a low pressure injection machine and injection molds. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Production of Ti-35Nb alloy by powder metallurgy for aerospace application

Titanium and its alloys provide high strength-to-weight ratios, good fatigue strength and increased corrosion resistance compared with others materials. Its acceptance in aerospace has been limited by costs considerations such as high cost of raw material, high buy-to-fly ratios and expensive machining operations. Significant cost reductions can be obtained by vacuum sintering and powder metallurgy (P/M) techniques by producing near net shapes and consequently minimizing material waste and machining time. The Ti 35Nb alloy exhibit a low modulus of elasticity. Stemming from the unique combination of high strength, low modulus of elasticity and low density, this alloy is intrinsically more resistant to shock and explosion damages than most other engineering materials. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by sintering between 900 and 1600 °C, in vacuum. Sintering behavior was studied by means of dilatometry. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Density was measured by Archimedes method. Copyright © 2004 Society of Automotive Engineers, Inc.

Gamma decay of the lowly excited states of 189Re

189W activities were produced via the 192Os(n, α) reaction using irradiation of isotopically enriched 192Os metallic powder of ～100 mg/cm2 with 14 MeV neutrons. The X-γ and γ-γ coincidence measurements were made so as to obtain γ rays from 189W decay and its coincidence relations. A new simple decay scheme of 189W including three γ rays of 210.2, 229.6 and 260.2 keV is proposed. Two new levels of 189Re at 470.4 and 489.8 keV are assigned.

A powder neutron diffraction study of the metallic ferromagnet Co3Sn2S2

Variable-temperature powder neutron diffraction data reveal that Co3Sn2S2 crystallizes in the shandite structure (space group R (3) over barm, a = 5.36855(3)angstrom, c = 13.1903(1) angstrom at 300 K). The structural relationship between Co3Sn2S2 and the intermetallic compound CoSn, both of which contain Kagome nets of cobalt atoms, is discussed. Resistivity and Seebeck coefficient measurements for Co3Sn2S2 are consistent with metallic behaviour. Magnetic susceptibility measurements indicate that Co3Sn2S2 orders ferromagnetically at 180(10) K, with a saturation moment of 0.29 mu(B) per cobalt atom at 5 K. The onset of magnetic ordering is accompanied by marked anomalies in the electrical transport properties. (c) 2008 Elsevier Masson SAS. All rights reserve

Morphological Evolution in Air-Stable Metallic Iron Nanostructures and Their Magnetic Study

Iron nanostructures with morphology ranging from discrete nanoparticles to nearly monodisperse hierarchical nanostructures have been successfully synthesized using solvated metal atom dispersion (SMAD) method. Such a morphological evolution was realized by tuning the molar ratio of ligand to metal. Surface energy minimization in confluence with strong magnetic interactions and ligand-based stabilization results in the formation of nanospheres of iron. The as-prepared amorphous iron nanostructures exhibit remarkably high coercivity in comparison to the discrete nanoparticles and bulk counterpart. Annealing the as-prepared amorphous Fe nanostructures under anaerobic conditions affords air-stable carbon-encapsulated Fe(0) and Fe3C nanostructures with retention of the morphology. The resulting nanostructures were thoroughly analyzed by powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and Raman spectroscopy. TGA brought out that Fe3C nanostructures are more robust toward oxidation than those of a-Fe. Finally, detailed magnetic studies were carried out by superconducting quantum interference device (SQUID) magnetometer and it was found that the magnetic properties remain conserved even upon exposure of the annealed samples to ambient conditions for months.

Crystallographic and electrochemical characteristics of Ti45Zr35Ni17Cu3 quasicrystalline alloy ball-milled with nickel powder

Crystallographic and electrochemical characteristics of ball-milled Ti45Zr35Ni17Cu3 +xNi (x = 0, 5, 10, 15 and 20 mass%) composite powders have been investigated. The powders are composed of amorphous, I- and Ni-phases when x increases from 5 to 20. With increasing x, the amount of Ni-phase increases but the quasi-lattice constant decreases. The maximum discharge capacity first increases as x increases from 0 to 15 and then decreases when x increases further from 15 to 20. The high-rate dischargeability and cycling stability increase monotonically with increasing x. The improvement of the electrochemical characteristics is ascribed to the metallic nickel particles highly dispersed in the alloys, which improves the electrochemical kinetic properties and prevents the oxidation of the alloy electrodes, as well as to the mixed structure of amorphous and icosahedral quasicrystal line phases, which enhances the hydrogen diffusivity in the bulk of the alloy electrodes and efficiently inhibits the pulverization of the alloy particles.

Powder Diffraction of Components Subject to Corrosion in Fuse Cutouts with CeramicInsulation

Aiming identification of the components most affected by corrosion under saline environment conditions, we have carried out X-ray diffraction measurements in ceramic and bond materials, all in the powder form. The ceramic is analyzed before and after thermal annealing at 1000 degrees C, showing the same DRX peaks, although better defined after annealing. Identification suggests the presence of Al(6)Si(2)O(13) (Mullite) and SiO(2) (Quartz). Analysis of the junction (bond) material shows similar peaks, but a metallic preponderance is observed. Thermal annealing of the junction is done at much lower temperature, because it melts in the range 135 degrees C-170 degrees C, when a whitish smoke begins to show up along with strong sulfur odor.

Production of a low young modulus titanium alloy by powder metallurgy

Titanium alloys have several advantages over ferrous and non-ferrous metallic materials, such as high strengthto-weight ratio and excellent corrosion resistance. A blended elemental titanium powder metallurgy process has been developed to offer low cost commercial products. The process employs hydride-dehydride (HDH) powders as raw material. In this work, results of the Ti-35Nb alloy sintering are presented. This alloy due to its lower modulus of elasticity and high biocompatibility is a promising candidate for aerospace and medical use. Samples were produced by mixing of initial metallic powders followed by uniaxial and cold isostatic pressing with subsequent densification by isochronal sintering between 900 up to 1600 °C, in vacuum. Sintering behavior was studied by means of microscopy and density. Sintered samples were characterized for phase composition, microstructure and microhardness by X-ray diffraction, scanning electron microscopy and Vickers indentation, respectively. Samples sintered at high temperatures display a fine plate-like alpha structure and intergranular beta. A few remaining pores are still found and density above 90% for specimens sintered in temperatures over 1500 °C is reached.

BaTiO3 obtained through metallic stearate precursors

Metallic stearates were used as precursors to obtain BaTiO3. Barium and titanium stearate mixtures were homogenized in ball mill containing some amount of ammonium stearate. The mixture of the precursors was evaluated by simultaneous TG/ DTA and TMA, and residues from thermal decomposition were characterized by XRD and SEM. It could be verified that the residues from the thermal decomposition in both oxidant and inert atmospheres were the BaTiO3 but with characteristic morphological and crystalline aspects depending on the experimental conditions in which the mixtures of precursors were obtained. (C) 2002 Elsevier B.V. B.V. All rights reserved.

High activity photocatalyst powder formed by three ceramic oxides

A Photocatalyst ceramic powder that presented high photoactivity based on TiO2 modified with 25% molar of SnO2 and up to 5% molar of Ag2O was obtained in the present work. The aforementioned ceramic powder was obtained using all commercial oxides as well as the oxides mixture technique. The powders were ground in high energy mill for one hour with subsequent thermal treatment at 400°C for four hours. They were, furthermore, characterized using surface area of around 6m2/g, where the X-Ray diffraction results provided evidence for the presence of anatase and rutile phases, known to be typical characteristics of both the TiO2 and SnO2 used. During the thermal treatment, Ag2O was reduced to metallic silver. The photodegradation rehearsals were carried out using a 0.01 mmol/L Rhodamine B solution in a 100mg/L photocatalyst suspension in a 500ml beaker, which was irradiated with 4W germicide Ultraviolet light of 254nm. In addition, samples were removed after duration of about 10 minutes to an hour, where they were analyzed thoroughly in UV-vis spectrophotometer. The analysis of the results indicated that for the compositions up to 2.5% molar of Ag2O, the photoactivity was found to be greater than that of Degussa P25 photocatalyst powder, and as such it was then used as a reference. Taking into account 90% degradation of Rhodamine B, a duration period of 11 minutes was obtained for the developed photocatalyst powder compared to the 38 minutes observed for the Degussa P25. FEG-SEM micrographies enabled the verification of the morphology as well as the interaction of the oxide particles with the metallic silver, which led us to propose a model for the increase in photoactivity observed in the photocatalyst powder under investigation.

INVESTIGATION OF AIR JIGGING AND AIR CLASSIFICATION TO RECOVER METALLIC PARTICLES FROM ANALYTICAL SAMPLES

Analyzing “nuggety” gold samples commonly produces erratic fire assay results, due to random inclusion or exclusion of coarse gold in analytical samples. Preconcentrating gold samples might allow the nuggets to be concentrated and fire assayed separately. In this investigation synthetic gold samples were made using similar density tungsten powder and silica, and were preconcentrated using two approaches: an air jig and an air classifier. Current analytical gold sampling method is time and labor intensive and our aim is to design a set-up for rapid testing. It was observed that the preliminary air classifier design showed more promise than the air jig in terms of control over mineral recovery and preconcentrating bulk ore sub-samples. Hence the air classifier was modified with the goal of producing 10-30 grams samples aiming to capture all of the high density metallic particles, tungsten in this case. Effects of air velocity and feed rate on the recovery of tungsten from synthetic tungsten-silica mixtures were studied. The air classifier achieved optimal high density metal recovery of 97.7% at an air velocity of 0.72 m/s and feed rate of 160 g/min. Effects of density on classification were investigated by using iron as the dense metal instead of tungsten and the recovery was seen to drop from 96.13% to 20.82%. Preliminary investigations suggest that preconcentration of gold samples is feasible using the laboratory designed air classifier.

Measurements of the Magnetic Permeabilities of the Iron-Manganese Alloy System Prepared by the Methods of Powder Metallurgy

Powder metallurgy is a branch of metallurgy which produces metallic compacts in their final forms by means of pressure and heat-treatment from the pow­ders. The products of powder metallurgy are being used in our daily lives quite often. For example, the tungsten wires in the electric bulbs to the silver-tin fillings of our teeth.

The Corrosion Resistance of Iron-Tin Compacts as Produced by Powder Metallurgy

The art of Powder Metallurgy deals with the preparation of metal powders and their utilization. As a more pertinent definition, the following has been suggest­ed: "Powder Metallurgy is the art of producing metal powders and shaped objects from individual, mixed, or alloyed metal powders, with or without the inclusion of non-metallic consti­tuents".

Manufacturing of self-passivating tungsten based alloys by different powder metallurgical routes

Self-passivating tungsten based alloys will provide a major safety advantage compared to pure tungsten when used as first wall armor of future fusion reactors, due to the formation of a protective oxide layer which prevents the formation of volatile and radioactive WO3 in case of a loss of coolant accident with simultaneous air ingress. Bulk WCr10Ti2 alloys were manufactured by two different powder metallurgical routes: (1) mechanical alloying (MA) followed by hot isostatic pressing (HIP) of metallic capsules, and (2) MA, compaction, pressureless sintering in H2 and subsequent HIPing without encapsulation. Both routes resulted in fully dense materials with homogeneous microstructure and grain sizes of 300 nm and 1 μm, respectively. The content of impurities remained unchanged after HIP, but it increased after sintering due to binder residue. It was not possible to produce large samples by route (2) due to difficulties in the uniaxial compaction stage. Flexural strength and fracture toughness measured on samples produced by route (1) revealed a ductile-to-brittle-transition temperature (DBTT) of about 950 °C. The strength increased from room temperature to 800 °C, decreasing significantly in the plastic region. An increase of fracture toughness is observed around the DBTT.

Powder painting of aluminium

The mechanisms involved in the production of chromate-phosphate conversion coatings on aluminium have been investigated. A sequence of coating nucleation and growth has been outlined and the principle roles of the constituent ingredients of the chromate-phosphate solution have been shown. The effect of dissolved aluminium has been studied and its role in producing sound conversion coatings has been shown. Metallic contamination has been found to have a dramatic influence on chromate-phosphate coatings when particular levels have been exceeded. Coating formation was seen to be affected in proportion to the level of contaminaton; no evidence of sudden failure was noted. The influence of substrate and the effect of an acidic cleaner prior to conversion coating have been studied and explained. It was found that the cleaner ages rapidly and that this must .be allowed for when attempting to reproduce industrial conditions in the laboratory. A study was carried out on the flowing characteristics of polyester powders of various size distributions as they melt using the hot-stage microscopy techniques developed at Aston. It was found that the condition of the substrate (ie extent of pretreatment), had a significant effect on particle flow. This was explained by considering the topography of the substrate surface. A number of 'low-bake' polyester powders were developed and tested for mechanical, physical and chemical resistance. The best formulation had overall properties which were as good as the standard polyester in many respects. However chemical resistance was found to be slightly lower. The charging characteristics of powder paints during application by means of electrostatic spraying was studied by measuring the charge per unit mass and relating this to the surface area. A high degree of correlation was found between charge carried and surface area, and the charge retained was related to the powder's formulation.