Effects of the electric current on conductive Si3N4/TiN composites in spark plasma sintering

► Presence of TiN improved the densification of both α-Si3N4 and β-Si3N4 clearly. ► α–β Transformation of silicon nitride is promoted by the presence of TiN. ► Aspect ratio and porosity of Si3N4/TiN composites is lower than monolithic Si3N4. ► Mechanical properties of Si3N4/TiN composites increases with increase of conductivity. The effect of the electric current in spark plasma sintering (SPS) process on the densification, phase transformation, microstructure and mechanical properties of conductive Si3N4/TiN composites was studied in comparison with non-conductive monolithic α-Si3N4 and β-Si3N4. In SPS, the densification and α–β transformation of Si3N4 were enhanced by the presence of the highly conductive TiN phase, in contrast to its opposite effect in Hot Pressing. The densification of the conductive Si3N4/TiN composites took place at about 100°C lower than that for the non-conductive monolithic Si3N4. Although TiN grains suppressed the formation of elongated β-Si3N4 grains, the beneficial effect of TiN on densification resulted in Si3N4/TiN composites with improved fracture toughness and hardness. The experimental results presented here combined with the literature data suggest that the effects of the presence of TiN on SPS sintered Si3N4 are derived from the increase in the electric current passing through the samples.