THERMODYNAMICALLY STABLE BETA[NI(AL,TI)]-BETA'[NI2ALTI]-GAMMA'[NI-3(AL,TI)] METAL-METAL COMPOSITES

Single-phase intermetallic compounds are often quite brittle. Experiments are reported in which a metallic composite consisting of three different intermetallic compounds (beta, beta', and gamma') in the Ni-Ti-Al system was fabricated by extruding a mechanical mixture of the compounds. In this way, the microstructure could be engineered to disperse the most ductile intermetallic in between the more brittle components. An additional feature was to choose the beta, beta', and gamma' powders with compositions which allowed them to coexist in equilibrium when coextruded to form the composite. It is found that this approach confers elevated temperature microstructural stability, a crack arresting ability, reasonable ductility, and considerable strength even at high temperatures.