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.