Effect of in-situ formed MoSi2 on phase transformation and thermal diffusivity of spark plasma sintered silicon nitride

Dense silicon nitride - Molybdenum disilicide (Si3N4-MoSi2) was prepared by spark plasma sintering (SPS) of the Si3N4 and Mo powder mixture with 7 mol% CeO2 sintering additives. The sintering time and sintering temperature were optimized, and the effect of in-situ formed MoSi2 on the microstructure, phase transformation and thermal diffusivity of Si3N4 ceramic was investigated. The α - β transformation ratio and the thermal diffusivity of Si3N4 ceramic composites were both higher than the monolithic Si3N4 that had a β:α ratio of 84.3:15.7 and the thermal diffusivity of 10.24 mm2/s. Furthermore, the Si3N4 ceramic composites densified by two-stage SPS exhibited 100% β phase ratio of Si3N4, and the highest thermal diffusivity of the composites was 23.17 mm2/s when the content of Mo particles was under 6 wt%. The in-situ synthesis of MoSi2 is proposed as explaining the improvement of α to β-phase transformation and thermal diffusivity of Si3N4 ceramic composites, due to the enhanced SPS process.