Optimizaton of Mo-Si-B intermetallic alloys

Mo-Si-B intermetallics consisting of the phases MO3Si and Mo5SiB2, and a molybdenum solid solution ("alpha-Mo"), have melting points on the order of 2000 degreesC. These alloys have potential as oxidation-resistant ultra-high-temperature structural materials. They can be designed with microstructures containing either individual alpha-Mo particles or a continuous alpha-Mo phase. A compilation of existing data shows that an increase in the volume fraction of the alpha-Mo phase increases the room-temperature fracture toughness at the expense of the oxidation resistance and the creep strength. If the a-Mo phase could be further ductilized, less alpha-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.