Spark plasma extrusion (SPE): Prospects and potential K. Morsi, * A. El-Desouky, B. Johnson, A. Mar and S. Lanka Department of Mechanical Engineering, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182, USA Received 25 March 2009; revised 14 April 2009; accepted 14 April 2009 Available online 22 April 2009 Despite the advantages of spark plasma sintering, it has so far been limited to the processing of simple shapes, due to its inherent geometric conﬁguration. This paper discusses the prospects and potential of spark plasma ‘‘extrusion” as a process that can allow the production of extended geometries via electric-current processing. Results on the spark plasma extrusion and properties of alu- minum are also discussed, showing the feasibility of this processing approach, which has major implications for the spark plasma sintering ﬁeld. Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Powder processing; Powder consolidation; Extrusion; Hot working; Aluminum Spark plasma sintering (SPS) of metallic powder involves the passage of pulsed electric current through powder while subjected to an applied pressure. Advanta- ges of the process include sintering at signiﬁcantly lower sintering temperatures, shorter sintering times, higher heating rates and much faster phase transformation kinetics than conventionally possible [1]. The process has been applied to a wide range of materials including nanopowders [2], biomaterials [3], carbon nanotube ceramic composites [4], titanium dual matrix composites [5], shape memory materials [6], intermetallics [7] and transparent ceramics [8]. It is clear that SPS will remain a very important pro- cess for some time to come. However, most research so far has been focused on the processing of simple shapes. Due to the recent intense research and the now docu- mented remarkable advantages of SPS [9], its extension to spark plasma extrusion (SPE) has major implications, including the production of powder-based materials of extended geometries. Other implications include the potential generation of new unique microstructures due to the eﬀect of stress-induced deformation under the inﬂuence of electric current. In addition, material recrys- tallization under the inﬂuence of current during SPE can lead to grain reﬁnement, which would not normally occur in SPS. It is noteworthy that high electric current density has been shown to decrease the ﬂow stress of met- als, and work by Conrad and co-workers have focused on examining this eﬀect in more detail, in addition to establishing a fundamental understanding of mecha- nisms involved [10]. They reported that above critical current densities of 1000–10,000 A cm 2 strain rates were observed to increase by orders of magnitude. It is therefore fair to expect in SPE a reduction in extrusion temperature requirements as well as extrusion pressure at some critical current density. Apart from limited work on the electric rolling of powders [11,12], a literature search by the authors did not reveal any publications on the SPE or electric extrusion of powder-based materi- als. A patent search, though, did reveal that a continuous extrusion apparatus that uses electric current as a means to uniformly heat and simultaneously sinter and ‘‘contin- uously” extrude electrically conductive granulated mate- rials (using ceramic extrusion containers/tooling) had in fact been patented in 1983 [13] (hence the origination of the idea must be placed there), which was before the thrust of the research on SPS [14]. However, to date the SPE of powder-based materials remains a largely vir- gin area from the research point of view, with many ques- tions needing still to be answered and disseminated to the scientiﬁc community. These include:  What is the eﬀect of combined deformation and elec- tric current activation on the recovery and recrystalli- zation behavior of extruding materials?  What is the eﬀect of current density, extrusion speed and extrusion ratio on the activation energy for extru- sion, deformation mechanisms, extrusion pressure requirements and resulting microstructures? 1359-6462/$ - see front matter Ó 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2009.04.026 * Corresponding author. E-mail: kmorsi@mail.sdsu.edu Available online at www.sciencedirect.com Scripta Materialia 61 (2009) 395–398 www.elsevier.com/locate/scriptamat