Papers by Keyword: Metallic Powder

Abstract: The article describes the main characteristics of powders of a cobalt alloy and alloyed high carbon steel, which were produced by electroerosion dispersion in the environment of distilled water. The areas for further processing of the powders, depending on the size, morphology and fraction composition of particles were identified in the aim of the best use of the resulting powders, and reducing waste.

Abstract: Low-pressure metal injection molding (LP-MIM) is an advanced manufacturing technology where a wax-based feedstock is injected into a complex shape before densification heat treatments. Feedstock is generally designed to minimize segregation, maximize flowability, maximize the strength of the molded component, maximize the solid loading potential and ease of debinding. In this study, the emphasis is placed on the evaluation of the effect of segregation on different wax-based Inconel 718 superalloy feedstocks used in LP-MIM. In powder metallurgy, particle or phase segregation generates a fluctuation of the particle distribution in powder-binder mixtures from point to point. Such demixing generally occurs before or during the injection process, and can lead to the formation of defects such as cracks, distortions or heterogeneous shrinkage of the sintered parts. Different wax-based feedstocks were poured in cylindrical hot molds (95°C), maintained in molten state for 1 minutes or for 60 minutes, and rapidly cooled to room temperature. The specimens were then extracted from the top and bottom regions of each cylindrical part. A thermogravimetric analysis technique was used to measure the volume fraction of powder at these two locations in order to quantify the degree of segregation in green parts. The best candidate feedstocks minimizing segregation are the mixtures containing only paraffin wax, or those containing paraffin wax and ethylene vinyl acetate combined. An increase in the time spent in the molten state and the use of beeswax or stearic acid promote the powder-binder separation of feedstocks.

Abstract: Powder forming involves fabrication of a preform by conventional press-and-sinter processing, followed by various forming processes, citing as examples, rolling, compaction, forging, extrusion, among others, of the porous preform into a final shape through substantial densification. This work makes a finite element analysis for porous metals. The finite element model was applied to simulating the case of compaction of nanocristalline copper under uniaxial compression conditions in order investigate the densification behavior. The model was simulated using explicit integration method as applied to the evolution variation of the relative density and the dislocation density of the compact. Finite element analysis program used was Abaqus. Finite element calculations were compared with literature data. The agreements between finite element model and literature results for densification of nanocristalline copper were good.

Abstract: Dynamic modeling of compaction process ,and evaluation of hardening parameters of powder compacts undergoing uni-axial/multi compaction is a tedious process and requires many elaborate tests .However ,assuming a two-parameter failure surface ( such as Mohr–Coulomb),evolution of failure surface may be monitored by two points on the failure surface. Results of uni-axial compression and direct or indirect tensile tests may readily provide the two required points. In order to assess this hypothesis ,a laboratory investigation was carried out using atomized iron powder(WPL-200) and aluminum powder(+160Mm) . Green compacts of the said drop-hammer , specifically designed for this purpose. Specimens with various relative compactions were produced and tested in uni-axial compression test and Brazilian split test .Variations of compressive/tensile strength with compaction energy(hammer speed) and relative density were studied and hardening law for green compacts were developed.

Abstract: This paper presents a study on the electrothermal explosion of metallic powders produced by a pulsed high voltage generator, which is a fast-discharge capacitive storage device. The character of instantaneous current, voltage were measured and studied. The energy-utilization ratio was calculated and analyzed. It is shown that the maximum current density and current rise rate obtained during electrothermal explosion of Cu powder were of the order of 10⁸A/cm² and 10¹³A/s, respectively. The total energy deposited on exploding was 38.57%~65.90% of the total electrically stored energy, and increased with the charging voltage and powder masses exploding increasing. Meanwhile, the electrical energy applied to the powder was estimated to be about 1.5~2 times the energy theoretically required to vaporization of the powder and metallic exploding. And the energy input in exploding supplied by circuit increased with the charging voltage and the metallic powder conductor height increasing.

Abstract: Welding materials, that the principal chemical component is nickel, are used usually for the welding between copper and austenitic stainless steels. But many kinds of mechanical or physical properties of welds between two materials will change largely. In this study, Functionally Graded Piping Joints (FGPJ) have been manufactured as an experiment using copper and austenitic stainless steel (SUS304) powder by a process based on HIP. This composition has been confirmed by absorbed electron and characteristics X-ray images of each mixed layer for FGPJ to be uniform or continuous. The following items have been investigated and compared with the linear law of mixture rule: Vickers hardness, thermal expansion, and thermal conductivity at a one-dimensional non-steady state etc. Those physical properties have been identified to depend on the mixing ratios of copper and austenitic stainless steel (SUS304). Pretty good agreements have been obtained between the experimental data and the calculated values according to the linear law of mixture rule.

Abstract: It is known from experimental data that bulk metallic samples reflect microwaves while powdered samples can absorb such radiation and be heated efficiently. In the present paper we investigate theoretically the mechanisms of penetration of microwave radiation through a layer of metallic powder and microwave heating of such system.

Abstract: . It is known that bulk metallic samples reflect microwaves (MWs) while metallic powdered samples can absorb such radiation and be heated efficiently. The present paper shows a direct evidence of penetration of MW radiation into and through a layer of metallic powder and contains theoretical explanation of such behavior.

Abstract: The rising of consumers’ demands and an ever increasing pressure of international markets imposed a deep change in the product development process to respond to an increasing product complexity and higher quality, as well to the need to promptly introduce products into the market. Stereolithography plays an important role on this new product development context. This technology produces models for thermosetting resins through a polymerisation process that transforms liquid resins into solid materials. In this work, a new route to produce metallic parts through stereolithography is explored. The curing analysis of hybrid reinforced polymeric systems, polymerised through radicalar or/and cationic mechanisms, is investigated. The rheological behaviour of these polymeric systems is also evaluated due to its importance for recoating. The influence of other processing and material characteristics like light intensity, initiator concentration, low powder size of metallic powders, degree of dilution, etc. is also investigated.

Abstract: The conditions needed for an efficient separation together with the most important factors influencing the accuracy of the separation are emphasized. Some relationships that allow the evaluation of the covering degree of the separation surface and the volume of the charge with single dimension particles corresponding to a unit separation surface are presented. The efficiency of spherical shape particles separation and the productivity of the separation process have been analysed. Some technical and practical considerations on the separation process are given.