Optimizaton of Mo-Si-B Intermetallic Alloys

Mo-Si-B intermetallics consisting of the phases Mo3Si and Mo5SiB2, and a molybdenum solid solution (“ -Mo”), have melting points on the order of 2000 °C. These alloys have potential as oxidationresistant ultra-high-temperature structural materials. They can be designed with microstructures containing either individual -Mo particles or a continuous -Mo phase. A compilation of existing data shows that an increase in the volume fraction of the -Mo phase increases the room-temperature fracture toughness at the expense of the oxidation resistance and the creep strength. If the -Mo phase could be further ductilized, less -Mo would be needed to achieve an adequate value of the fracture toughness, and the oxidation resistance would be improved. It is shown that microalloying of MoSi-B intermetallics with Zr and the addition of MgAl2O4 spinel particles to Mo both hold promise in this regard.