Superplasticity in nanocrystalline Ni 3Al

Abstract

Tensile testing at constant strain rate and temperature has shown that superplasticity can be observed at lower temperatures in nanocrystalline materials than in the microcrystalline state. However, even at lower superplastic temperatures the onset of superplastic deformation in nanocrystalline materials coincides with microstructural instability. Consequently, ordered intermetallics such as Ni 3Al are attractive systems for the study of nanocrystalline superplasticity because grain growth kinetics is inhibited by preferred atomic pairing. Ni 3Al was processed by severe plastic deformation to obtain nanocrystalline samples. The strain rate sensitivity, n, was estimated from strain rate jump tests to be 2.6. The grain size dependence of superplastic flow, p, was estimated by testing tensile specimens annealed to produce a range of grain size. The value of p was estimated to be 2.4–1.8. Several interesting features of nanocrystalline superplasticity, such as strain hardening and high flow stresses, were investigated.