Coupled thermo-electric discrete element model for spark plasma sintering

Spark Plasma Sintering (SPS) is an emerging powder consolidation technique that employs electric current to generate heat through the Joule effect while applying pressure to achieve densification efficiently. A common concern in this process is the localization of Joule heat at the contacts between particles where electrical resistance is highest. This study investigates the coupled thermo-electric phenomena in sintered material using an original discrete element model (DEM). The model employs a two-particle sintering geometry, with particles interconnected by the neck. Neck size is evaluated using volume preservation criteria, and a correction factor compensating for non-physical overlaps as well as additional grain boundary resistance is introduced. The DEM model is verified by comparing with FEM simulations. A simple three-particle geometry is used to demonstrate that the simple DEM model gives the same potential evolution, resultant currents and temperature evolution as the more complex finite element model. Thereafter, the DEM model is validated on geometry generated using real particle size distribution to ensure heterogeneous microstructure. The effect of density on the electrical potential evolution, Joule heating and resulting increase in temperature is analysed. It is shown that the Joule heat is concentrated in the smaller particles and is conducted throughout the sample, resulting in a homogeneous increase in temperature. Ultimately, the effect of densification on heating rate is analysed. This study improves the overall understanding of thermo-electric behaviour in the SPS process, providing significant insights into the microscopic phenomena.