Microstructures and Mechanical Properties of Ni-Nb Aluminides Produced by MA Process

Abstract

Of all the intermetallics that belong to Ni-Nb-Al system, (Ni₃Al+Ni₃Nb), (NiAl+NiAlNb), (NiAl+Ni₃Al), NiAl and Ni₃Al 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 μm and relative density above 96%. The combination of high strength and large fracture strain of more than 10% at room temperature was confirmed by compression test for each aluminide except for both (NiAl+NiAlNb) and (Ni₃Al+Ni₃Nb). At high temperatures, these aluminides exhibited a steady state deformation and no fracture during the testing. The strain rate sensitivity exponent (m value) of more than 0.3 was obtained for alloys except NiAl. Especially the highest value of m (>0.6) was observed for (Ni₃Al+Ni₃Nb) at 1 173 K. Such large m value more than 0.3 is believed to be associated with the development of superplasticity.