Discrete Finite-Element Simulation of Thermoelectric Phenomena in Spark Plasma Sintering JING ZHANG 1,3 and ANTONIOS ZAVALIANGOS 2 1.—Department of Mechanical Engineering, University of Alaska Fairbanks, Fairbanks, AK 99775, USA. 2.—Department of Materials Science and Engineering, Drexel University, Philadelphia, PA 19104, USA. 3.—e-mail: jzhang6@alaska.edu Realistic microstructures of compacted powders formed by spark plasma sin- tering or field-activated sintering technology were modeled using the discrete finite-element method. Two key thermoelectric characteristics were studied: (1) the effect of the electric current pattern, i.e., direct current (DC) and pulsed current, on temperature distributions in the compacted powders, and (2) the effect of compaction modes, i.e., isostatic compaction and uniaxial compaction, on conductivity. Simulations showed that, for the same electric power input, pulsed current offered faster heating and more uniform temperature distri- bution in the compact than did DC. Additionally, using uniaxial compaction, the effective conductivity of the compact in the compaction direction was higher than in the transverse direction, by as much as 20%. Experimental measurements confirmed the existence of anisotropy of conductivity in the compact. Key words: Discrete finite-element simulation, thermoelectric phenomena, spark plasma sintering, field-activated sintering technology, modeling, anisotropy, conductivity, pulse effect INTRODUCTION Spark plasma sintering (SPS) or field-activated sintering technology (FAST) is a nonconventional powder consolidation method in which densification is achieved by application of electric current and mechanical pressure. Although there have been many successful applications of SPS or FAST in material syntheses, current understanding of the effect of electric pulses on the compact is still incomplete. A few experiments have been conducted to compare the temperature or density of a compact processed by using direct current (DC) and pulsed current. Nishimoto et al. 1 showed that the densifi- cation rate of Fe- and Ni-based alloys was about 5% faster when using pulsed current rather than direct current. Inoue 2 claimed in his patent that there was a frequency-dependent effect. Additionally, thermal properties of densified materials in SPS or FAST are crucial, because temperature distributions are pri- marily affected by conductivity. Many researchers have attempted to measure or model the effective thermal conductivity of particulate materials. 3–12 However, most thermal conduction work has been limited to the compact under isostatic stress or to thermal properties in an axial direction under uni- axial compaction. The result may not be applicable to large, complex-shaped compacts that experience nonisostatic stress. In this work, we use a modeling approach to compare differences in the temperature distribution in the compact for DC versus pulsed current, and we explore anisotropy of conductivity resulting from application of nonisostatic stress. METHOD We investigated the coupling between electrical, thermal, and mechanical responses, and the possi- bility of thermal anisotropy due to nonisostatic stress. The thermoelectric Thomson effect 13 can be included in this work; that is, if current density J (Received May 19, 2010; accepted February 12, 2011; published online March 9, 2011) Journal of ELECTRONIC MATERIALS, Vol. 40, No. 5, 2011 DOI: 10.1007/s11664-011-1606-0 Ó 2011 TMS 873