Synthesis of a (MoSi2, Mo5Si3)/SiC composite using an in situ solid-state displacement reaction between Mo2C and Si

Abstract

The intermetallic compound, MoSi2, has great potential as an elevated-temperature structural material but it exhibits some undesirable properties such as low fracture toughness and low strength at elevated temperatures. Improvement of these properties can be achieved by reinforcing MoSi2 with the addition of SiC particles or whiskers, or by alloying it with Mo5Si3. The preparation of MoSi2 composites from powders gives rise to an oxidation problem since SiO2 covers the raw powder. To avoid this problem, the material must be prepared in situ. In this work, multiphase composites based on the Mo-Si-C system have been prepared using a solid-state displacement reaction between Mo2C and Si. Samples were prepared from a mixture, containing different proportions of Si and Mo2C powders, which was pelletized under vacuum at 40 MPa and heat-treated in argon. The pieces obtained exhibit different proportions of SiC, MoSi2 and Mo5Si3. The microhardness obtained ranges from 12 to 14 GPa, and Kc is over 8 MPa·m1/2, which is higher than that of pieces made of MoSi2 only.