Spark plasma sintering in the presence of a liquid phase

Spark plasma sintering (SPS) is a modern sintering technique based on the application of pulses of direct electric current and pressure to the powder sample. SPS is often regarded as a solid state sintering technique. At the same time, in many studies, the formation of a liquid phase during SPS was observed as an effect concurrent to the powder consolidation. Furthermore, in some cases, the formation of a liquid phase was intentionally stimulated. In this article, we aim to analyze the origin of the liquid phase formation during SPS and discuss its role in the microstructure development of different materials. Two situations are considered: melting occurring when the whole sample reaches a temperature required for the liquid to appear and melting of local character associated with overheating of the inter-particle contacts. The problems of the description of the SPS processes with liquid phases involved are discussed and possible future research directions in this area are proposed.