Rapid formation of α-sialon during spark plasma sintering: Its origin and implications

α-Sialons with varied chemical compositions and starting precursors were sintered in spark plasma sintering (SPS) furnace to verify the influence of electrical conduction, mechanical pressure and heat transfer efficiency. The internal temperature that the sample was exposed to and its evolution during the heating were experimentally estimated and discussed. XRD and SEM grain size analysis were carried out to evaluate the phase and microstructure evolution. Mechanical pressure was eliminated to create a free sintering condition under SPS. By free sintering and surrounding the sample with graphite wool the heat transfer was sufficiently retarded and a usual slow reaction was demonstrated. It is verified that the efficiency of heat transfer is more influential in the enhancement of α-sialon formation and grain growth by SPS than the efficiency of electric conduction.