MoSi{sub 2} matrix composites have been recognized lately as potential materials for structural applications at elevated temperatures. Specifically, MoSi{sub 2} composites may exhibit useful properties at temperatures to 1400{degrees}C. Previous work improved the yield strength of MoSi{sub 2} at 1400{degrees}C by a factor of five through SiC whisker reinforcement. Current research is directed towards increasing the fracture toughness of MoSi{sub 2} through the addition of ductile phase reinforcements such as niobium and tantalum. The reaction between Nb and MoSi{sub 2} to form (Mo,Nb){sub 5}Si{sub 3} proceeds with faster kinetics at hot isostatic press temperatures as low as 1100{degrees}C when compared to the reaction between Ta and MoSi{sub 2} to form (Mo,Ta){sub 5}Si{sub 3}. This reaction product exhibits very poor properties, as evidenced by crack propagation through this layer during fracture. The feasibility of hot working these composites to produce tailored microstructures is examined. 11 refs., 10 figs.

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