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 40MPa and heat-treated in argon. The pieces obtained exhibit different proportions of SiC, MoSi₂ and Mo₅Si₃. The microhardness obtained ranges from 12 to 14GPa, and K_c is over 8MPa·m^1/2, which is higher than that of pieces made of MoSi₂ only.