On the Modernisation of Weber’s Electrodynamics

This work is an attempt to modernise Weber’s electrodynamics to make it compatible with the high-velocity regime, and with the existence of a limiting velocity, c. For this purpose, starting from the law of energy conservation and the mass–energy equivalence, new expressions for potential energy and for kinetic energy are derived jointly which are consistent with an ultimate velocity of the value of c. The new potential energy, already reported by Phipps, becomes Weber’s expression in the limit of low velocities. The new kinetic energy differs from the relativistic expression, but, like the latter, it also becomes the Newtonian expression in the limit of low velocities. New expressions for force and linear momentum are also derived which complete a new mechanics. Phipps’ potential energy and new kinetic energy are applied to the problem of two interacting charges in a radial motion and orbital motion. The new framework is also applied to the problem of a charge moving between the two plates of a charged capacitor, obtaining a result similar to that obtained by means of Maxwell–Lorentz electromagnetism and relativistic mechanics. The metaphysical considerations that clearly differentiate the conventional framework from the new framework proposed here are discussed

Amorphous Al-Ti Powders Prepared by Mechanical Alloying and Consolidated by Electrical Resistance Sintering

A novel processing method for amorphous Al50Ti50 alloy, obtained by mechanical alloying and subsequently consolidated by electrical resistance sintering, has been investigated. The characterisation of the powders and the confirmation of the presence of amorphous phase have been carried out by laser diffraction, scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and transmission electron microscopy. The amorphous Al50Ti50 powders, milled for 75 h, have a high hardness and small plastic deformation capacity, not being possible to achieve green compacts for conventional sintering. Moreover, conventional sintering takes a long time, being not possible to avoid crystallisation. Amorphous powders have been consolidated by electrical resistance sintering. Electrically sintered compacts with different current intensities (7–8 kA) and processing times (0.8–1.6 s) show a porosity between 16.5 and 20%. The highest Vickers hardness of 662 HV is reached in the centre of an electrically sintered compact with 8 kA and 1.2 s from amorphous Al50Ti50 powder. The hardness results are compared with the values found in the literature.Ministerio de Economía y Competitividad (Spain) / Feder (EU) DPI2015-69550-C2-1-PMinisterio de Economía y Competitividad (Spain) / Feder (EU) DPI2015-69550-C2-2-

Use of Urea and Ammonia to Produce High-Strength PM Aluminium Parts

Two methods to obtain bulk nanostructured aluminium parts are compared. The first one consists on milling Al powder in an ammonia gas atmosphere. In the second method, the Al powder is milled in vacuum with the addition of solid urea. In both cases, the milled powders are consolidated to full density by a conventional press-and-sinter powder metallurgy (PM) technique. The produced composites consist on a nanostructured aluminium matrix reinforced with self-forming nanocrystalline nitrides dispersoids. Consolidated compacts reach full densification, and show a high tensile strength (up to 550 MPa) and an outstanding high-temperature behaviour.Ministerio de Ciencia e Innovación DPI2009-0829

Medium-frequency electrical resistance sintering of oxidized C.P. iron powder

Commercially pure (C.P.) iron powders with a deliberate high degree of oxidation were consolidated by medium-frequency electrical resistance sintering (MF-ERS). This is a consolidation technique where pressure, and heat coming from a low-voltage and high-intensity electrical current, are simultaneously applied to a powder mass. In this work, the achieved densification rate is interpreted according to a qualitative microscopic model, based on the compacts global porosity and electrical resistance evolution. The effect of current intensity and sintering time on compacts was studied on the basis of micrographs revealing the porosity distribution inside the sintered compact. The microstructural characteristics of compacts consolidated by the traditional cold-press and furnace-sinter powder metallurgy route are compared with results of MF-ERS consolidation. The goodness of MF-ERS versus the problems of conventional sintering when working with oxidized powders is analyzed. The electrical consolidation can obtain higher densifications than the traditional route under non-reducing atmospheres.Ministerio de Economía y Competitividad DPI2015-69550-C2-1-PMinisterio de Economía y Competitividad DPI2015-69550-C2-2-

Electrical discharge consolidation of Al and Ti powders

In this paper, electrical-discharge-consolidation (EDC technique) experiments were carried out with an equipment based on the technology developed for the stud welding technology. The main advantage of the EDC technique is its high speed, on the order of milliseconds or less, which makes it particularly interesting when a high final porosity is aimed, or when the inherent nanostructure of the powders needs to be preserved. Compacts of Ti and Al were consolidated with this technique, both directly from loose powders and from cold pressed green compacts. Two different configurations (200 V – 66 mF and 800 V − 1.1 mF) were tested. Relative density, microhardness, electrical resistivity and metallographic and SEM studies were carried out to understand the changes in powder particles caused by the electrical discharge. The use of a high capacitance in the capacitors bank, despite the use of a lower voltage, results in a better consolidation process.Ministerio de Economía y Competitividad DPI2015-69550-C2-1-PMinisterio de Economía y Competitividad DPI2015-69550-C2-2-P

Magnetic properties of iron powder sintered by medium-frequency electrical resistance sintering

Medium-frequency electrical resistance sintering (MF-ERS) is a technique that uses the application of pressure and heat, heat coming from the Joule effect, simultaneously to metallic powders. In this study, this technique consolidates commercial iron powders, and the porosity distribution and hysteresis curves of the compacts were analysed. Compact consolidated by conventional powder metallurgy (PM) was compared with the results obtained

Polvos de Al-Al 3Ti obtenidos mediante aleado mecánico y tratamiento térmico

Polvos mezclados de aluminio y titanio ( 10 % en peso) han sido aleados mecánicamente en un molino Attritor, obteniéndose una solución metaestable de titanio en la matriz de aluminio. Se han estudiado los cambios producidos en la forma y tamaño de las partículas, estructura y microestructura, al variar el tiempo de molienda entre 2 y 10 h. El procesado final se realiza para un tiempo de 10 h, habiéndose disuelto aproximadamente un 9 % en peso de titanio. Finalmente, se realiza un tratamiento térmico a diversas temperaturas, hasta un máximo de 625 °C, lo que produce la precipitación de diversas fases, como distintas estructuras de AI3TÍ y AI4C3. La aparición de estas segundas fases es caracterizada en función de la temperatura de tratamiento utilizada

Ceramic dies selection for electrical resistance sintering of metallic materials

Processing metallic powders by electrical resistance sintering requires the use of insulating ceramics dies. Selecting the appropriate ceramic material according to the electrical, thermal and mechanical properties is a need. Dies produced with several ceramic materials have been tested during the production of cemented carbide in order to check their behaviour in the process and final product properties. Tialite/mullite, zircon/mullite, zirconium phosphate based ceramic, yttria-stabilized zirconia and sialon, in most cases with modified compositions and shaping processes in order to achieve a high density, have been tested. Dry powder processing by cold isostatic pressing and furnace sintering resulted to be the better process for dies production. The effect of die properties on the produced cemented carbide, and the behaviour and life of the die during the production have been analysed. Very smooth die surface increases the number of cycles withstood during metallic parts production, because of lower extraction stresses, as checked for sialon dies. Zirconium phosphate based dies, with low thermal conductivity, show the most densified hard metal parts surface.Pproject EFFIPRO (EU) FP7-2013-NMP-ICT-FoF GRANT AGREEMENT N° 6087

Nickel Porous Compacts Obtained by Medium-Frequency Electrical Resistance Sintering

A commercially pure (c.p.) nickel powder was consolidated by Medium-Frequency Electrical Resistance Sintering (MF-ERS). In this consolidation technique, a pressure and the heat released by a high-intensity and low-voltage electrical current are concurrently applied to a metal powder mass. A nickel powder with a high tap porosity (86%) and a low applied pressure (only 100 MPa) is chosen in order to be able to obtain compacts with different levels of porosity, to facilitate the study of the porosity influence on the compact properties. The influence of current intensity and heating time on the global porosity values, the porosity and microhardness distribution, and the electrical conductivity of the sintered compacts is studied. The properties of the compacts consolidated by MF-ERS are compared with the results obtained by the conventional powder metallurgy route, consisting of cold pressing and furnace sintering. A universal equation to describe the porosity influence on all the analyzed properties of powder aggregates and sintered compacts is proposed and validated

Medium-Frequency Electrical Resistance Sintering of Soft Magnetic Powder Metallurgy Iron Parts

The fabrication of soft magnetic Fe parts by the medium-frequency electrical resistance sintering (MF-ERS) technique is studied in this paper. This consolidation technique involves the simultaneous application to metallic powders of pressure and heat, the latter coming from the Joule effect of a low-voltage and high-intensity electric current. Commercially pure iron powder was used in the consolidation experiences. The porosity distribution, microhardness, electrical resistivity and hysteresis curves of the final compacts were determined and analysed. The results obtained were compared both with those of compacts consolidated by the conventional powder metallurgy (PM) route of cold pressing and vacuum furnace sintering, and with fully dense compacts obtained by double cycle of cold pressing and furnace sintering in hydrogen atmosphereFinancial support of the Ministerio de Economía y Competitividad (Spain) and Feder (EU) through the research projects DPI2015-69550-C2-1-P and DPI2015-69550-C2-2-P is gratefully acknowledged The authors also wish to thank the technicians J. Pinto, M. Madrid and M. Sánchez (University of Seville, Spain) for experimental assistanc