Superplasticity and cooperative grain boundary sliding in nanocrystalline Ni3Al

Cooperative grain boundary sliding (CGBS) has been shown to account for the majority of macroscopic strain seen in microcrystalline metallic systems undergoing superplastic deformation. While CGBS has been observed on the surface of microcrystalline samples deforming superplastically through the shifting of diamond scribe lines, there have been few transmission electron microscopy results showing such occurrences in the bulk of the material, or the details behind the micromechanism of CGBS. In this work, nanocrystalline Ni3Al produced via high-pressure torsion is deformed superplastically in the electron microscope. High-temperature (∼700 °C) in situ tensile testing shows the nature of CGBS at the nanoscale through direct observation of this phenomenon.