DEVELOPMENT OF CONTINUOUS-FIBER-REINFORCED MOSI2-BASE COMPOSITES

MoSi2-base composites are currently being developed as structural aerospace materials for use at temperatures up to 1400-degrees-C. Work is being carried out on improving high-temperature creep resistance and room temperature fracture toughness by continuous fiber reinforcement. Candidate fibers consist of high-strength ceramic fibers, such as SiC and single-crystal Al2O3, and ductile high-strength molybdenum and tungsten alloy fibers. Critical issues being addressed concerning development of refractory-metal-fiber-reinforced MoSi2-base composites include identification of diffusion barrier fiber coatings that prevent reaction between the fiber and matrix, identification of fabrication techniques that do not result in loss of fiber ductility and fiber coating integrity, and oxidation resistance. A key issue regarding the development of ceramic-fiber-reinforced MoSi2-base composites is identification of debond fiber coatings that provide necessary fracture toughness and damage tolerance. Additions of SiC and Si3N4 particulate to MoSi2 are effective in lowering matrix thermal expansion to match more closely that of reinforcing fibers. Mechanical properties and environmental resistance of composite systems will be discussed.