Enhanced particle rearrangement during liquid phase spark plasma sintering of silicon nitride-based ceramics

Densification evolution has been analysed in liquid phase assisted spark plasma sintering (SPS) of silicon nitride (Si3N4)-based materials. Monolithic ceramics with variable amounts of Al2O3/Y2O3 sintering additives, and carbon nanotubes (CNTs) containing Si3N4 composites have been considered. The shrinkage behaviour of SPSed monolithic Si3N4 showed a noticeable enhancement of the particle rearrangement stage, exhibiting a complete wetting of the grain boundary phase even for the lowest additive content (1.70 vol.%), unlike the corresponding hot pressed (HPed) material. An improvement of the liquid phase wetting by the presence of electromechanical forces is proposed to explain the enhanced densification occurring in the particle rearrangement stage of the SPS process. Furthermore, the addition of CNTs seems to increase the efficiency of this mechanism, decreasing the particle rearrangement temperature.