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-degrees-C. The effects of strain rate on the flow stress for Mo5Si3-, SiO2- and CaO-containing composites are presented. Effects of several processing routes and microstructural modifications on the mechanical behavior of MoSi2-Mo5Si3 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 MoSi2-Mo5Si3 eutectics prepared by arc melting. Initial results on microstructural modeling of the deformation and fracture of MoSi2-based composites are also reported.