Mechanical behavior and interface design of MoSi₂-based alloys and composites

The mechanical behavior of hot pressed MoSi₂-based composites containing Mo₅Si₃, SiO₂, CaO and TiC as reinforcing second phases was investigated in the temperature regime 1000-1300 °C. The effects of strain rate on the flow stress for Mo₅Si₃, SiO^-₂ and CaO-containing composites are presented. Effects of several processing routes and microstructural modifications on the mechanical behavior of MoSi^-₂Mo₅Si₃ composites are given. Of these four composite additions, Mo₅Si₃ and CaO produce strengthening of MoSi₂ in the temperature range investigated. SiO₂ greatly reduces the strength, consistent with the formation of a glassy phase at interface and interphase boundaries. TiC reduces the flow stress of MoSi₂ in a manner that suggests dislocation pumping into the MoSi₂ matrix. The strain rate effects indicate that dislocation creep (glide and climb) processes operate over the temperature range investigated, with some contribution from diffusional processes at the higher temperatures and lower strain rates. Erbium is found to be very effective in refining the microstructures and in increasing the hardness and fracture properties of MoSi₂Mo₅Si₃ eutectics prepared by arc melting. Initial results on microstructural modeling of the deformation and fracture of MoSi₂-based composites are also reported.