Development of Advanced Heat Resistant Aluminides Produced by ma Process

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The intermetallics that belong to Ni-Nb-Al system, (Ni_3Al+Ni_3Nb), (NiAl + NiNbAl), (NiAl+Ni_3Al), NiAl and Ni_3Al were produced by mechanical alloying(MA)process with a view to refining microstructures. MA was carried out in the attritor mill using pure nickel, pure niobium powder and NiAl prealloyed powder as starting materials. MA powders were consolidated using the vacuum hot pressing.Sintered aluminides showed fine grain structures with average grain diameter under 5 mu m and relative density above 96%. The combination of high strength and large fracture strain of more than 10% at room temperatures was confirmed by compression test for each aluminide except for both(Ni_3AI+Ni_3Nb) and (NiAl+NiNbAl). At high temperatures, these aluminides exhibited a steady state deformation and no fracture during testing. The strain rate sensitivity exponent of m (>O. 6) was observed for (Ni_3Al+Ni_3Nb) at 1173K. Such large m value more than 0.3 is believed to be associated with the development of superplasticity.