MoSi2-Si3N4 composites: Influence of starting materials and fabrication route on electrical and mechanical properties

The fabrication method and the mechanical and electrical properties of different MoSi2-Si3N4 composite materials were investigated. Commercially available individual compounds, one-stage combustion synthesized MoSi2-Si3N4 and submicron MoSi2 powders were used as starting materials, followed by hot pressing. It was found that the sintering atmosphere used, nitrogen or argon, had a significant effect on the phase composition, mechanical and electrical properties of the final materials. It was shown that in some cases partial nitridation of MoSi2 occurred with the formation of MoSi2-Mo5Si3-Si3N4 ternary composites. The electrical conductivity of the composites depends also on the microstructure of materials. It was shown that the composites fabricated using combustion synthesized MoSi2 powders (500 nm) are characterized by higher flexural strength at room temperature compared to those from commercial powders. On the other hand, the composites fabricated from the commercial powders had higher strength and fracture toughness at elevated temperatures (up to 1200 °C). For all composites, the strength decreased significantly at temperatures over 1000 °C due to the brittle-ductile transition of the MoSi2 phase.