A One-Dimensional Model of the Electrical Resistance Sintering Process
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THE conventional powder-metallurgy processing route fundamentally entails the cold compaction of powders to obtain a green compact, followed by a furnace sintering to obtain the final product. Although this method is the most commonly used technology in industrial processes, new alternatives are continuously investigated to improve, at least partially, the problems and deficiencies of the current technology. In this sense, the direct use of electricity as a means of sintering powders (both metals and ceramics) has been suggested and pursued numerous times, generally from an experimental viewpoint. A detailed review of the development of the different modalities of the electrical sintering has been carried out by Grasso et al.[1] The great diversity of proposed modalities could be grouped under the generic name of electric currentactivated/assisted sintering (ECAS). Recently, the expression field-assisted sintering techniques (FAST) have become popular. Indeed, the speed of the processes is the most remarkable characteristic and the common factor among these techniques. The high speed of the ECAS or FAST processes exhibits a significant advantage in that it renders the use of vacuum or inert atmospheres unnecessary. Moreover, similar to the J.M. MONTES and J. CINTAS, Associate Professors, and P. URBAN, Lecturer, are with the Metallurgy and Materials Engineering Group, Escuela Te´cnica Superior de Ingenierı´ a, University of Seville, Camino de los Descubrimientos s/n, 41092 Seville, Spain. Contact e-mail: [email protected] F.G. CUEVAS, Associate Professor, is with the Department of Chemistry and Materials Science, Escuela Te´cnica Superior de Ingenierı´ a, University of Huelva, Campus La Ra´bida, Carretera Palos s/n, 21819 Palos de la Frontera, Huelva, Spain. Manuscript submitted March 20, 2012. Article published online November 14, 2014 METALLURGICAL AND MATERIALS TRANSACTIONS A
effects of hot-press processes (where the FAST techniques are in some way included), the shape that parts acquired after their processing is definitive or near definitive (net-shape or near-net-shape technique). However, one of the problems frequently mentioned by researchers that have pursued the problem of the FAST techniques is related to the dies, especially in cases where the die must be electrically insulating. The unresolved problem of choosing a material that is acceptably durable and economically worthwhile is of great interest and requires an exhaustive study. Although the different FAST variants may appear to have many common aspects, detailed studies lead to the conclusion that the physical phenomena in each of the modalities are very different. One of the FAST techniques, the so-called electrical resistance sintering (ERS), was already described in 1933 by Taylor,[2] and later modified by Cremer[3] in 1944, although its systematic study was not carried out until some years later by Lenel,[4] around 1955. Later, the ERS technique has been revised by incorporating technical variations of different importance.[5–7] Essentially, the ERS entail
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