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

Superplasticity and Cooperative Grain Boundary Sliding in Nanocrystalline Ni3Al. Mara, N.A., Sergueeva, A.V., Mara, T.D., McFadden, S.X., Mukherjee, A.K.: Materials Science and Engineering A, 2007, 463[1-2], 238-44