Spark Plasma Sintering as a Multifield Processing Platform: Extended Fundamentals and Hybrid Electric Field–Assisted Routes

Spark plasma sintering (SPS) has evolved from a rapid powder-consolidation technique into a multifield processing platform capable of directing microstructural evolution through the controlled interaction of pulsed electric current, thermal gradients, and mechanical loading. This chapter establishes a critically synthesized, experimentally grounded framework that reinterprets SPS as a coupled charge–heat–mass-transport phenomenon operating far from equilibrium. Rather than treating Joule heating as the sole driving force, the analysis evaluates the relative credibility of microdischarge hypotheses, electroplasticity, localized current concentration, and interfacial activation mechanisms across metallic, ceramic, and composite systems. The discussion explicitly links these mechanisms to measurable outcomes, including density gradients, grain refinement, residual stresses, and interfacial cohesion. Building on this extended physical foundation, the chapter examines spark plasma extrusion (SPE), current-assisted metal infiltration (CAMI)/current-assisted infiltration sintering (CAIS), and pressureless SPS (PL-SPS) as technologically mature hybrid routes. Experimental results – such as grain-size refinement in extruded Cu and Al systems, functional gradients induced by controlled deformation, and high-integrity Mg/hydroxyapatite (HA) interfaces produced by electric-field-activated infiltration – demonstrate how field-assisted processing can be deliberately engineered rather than phenomenologically described. The chapter positions SPS and its derivatives as scalable, decision-oriented platforms for advanced materials design, offering both mechanistic clarity and actionable guidance for next-generation structural, biomedical, and multifunctional systems.