High strain rate superplasticity in mechanically alloyed nickel aluminides

Grain refining for three nickel aluminides such as γ′-Ni₃Al (25Al) and β-NiAl (49Al) single-phase intermetallics, and (γ′+β) two-phase intermetallic (34Al) has been attained by using a wet mechanical alloying and vacuum hot pressing process. The values of average grain size of the three compacted intermetallics were very close and as small as about 1.0 μm. The superplastic flow behaviors of the fine grain intermetallics were examined mainly by hot compression tests, together with some tensile tests. The compression tests were performed at the temperatures of 1073K-1273K and at an initial strain rate range from 1.4×10^-4s^-1 to 5.6×10^-2s^-1. The results obtained from the compression and tensile tests revealed that γ′ single-phase intermetallic (25Al) and (γ′+β) two-phase intermetallic (34Al) can be deformed superplastically at 1273K and at a high strain rate range of about 4×10^-3s^-1 ∼ 5.6×10^-2s^-1. However, β (49Al)single-phase intermetallics showed poor ductility in tensile tests, probably due to a cavity formation during the deformation. Grain boundary sliding accommodated by slip was considered to contribute much to the high strain rate superplasticity in the intermetallics including γ′ phase.