Structure and properties of ultrafine-grained MoSi2 + Si3N4 composites synthesized by mechanical alloying

Monolithic MoSi2 and MoSi2 + Si3N4 ultrafine-grained composites with 2.5 or 5.0 wt.% Si3N4 were synthesized by mechanical alloying. The microstructure and crystal structure of the phases present in the as-milled powders were determined by electron microscopy and X-ray diffraction methods. The mechanically alloyed powders were successfully consolidated to full density by vacuum hot pressing. A detailed microstructural investigation and mechanical properties (hardness and fracture toughness) evaluation of the consolidated products was presented. After consolidation, the microstructure continued to be fine-grained (in the submicron range), but no appreciable increase in the room temperature fracture toughness of MoSi2 was observed for the composites by the addition of Si3N4.