Significant differences have been observed in the deformation characteristics of nanocrystalline materials at elevated temperatures as compared to their microcrystalline counterparts. This includes significantly higher flow stresses and much enhanced strain hardening rates in nanocrystalline structure. Conventional understanding on elevated temperature crystalline plasticity cannot explain these observations. Cooperative grain boundary sliding (CGBS) has 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 no TEM results showing occurrence in the bulk of the material, and the details behind the micromechanism of CBGS. In this work, nanocrystalline Ni3Al produced via High Pressure Torsion is deformed superplastically in the TEM. High-temperature (~700 C) in-situ tensile testing shows the nature of CGBS at the nanoscale through direct observation of this phenomenon. The second part of this presentation is devoted to demonstrating the potential of using spark plasma sintering (SPS) equipment to consolidate nanocrystalline powder ceramics and the subsequent superplastic deformation of the compact to near-finished shape. This procedure has provided one of the lowest temperature, high strain rate superplastic formings of nanocrystalline ceramics to date. Time permitting; the authors would also like to present the superplastic properties of carbon nanotube-reinforced alumina nanocomposites at ultralow temperature deformation in the SPS environment. This investigation is funded by grants from the U.S. National Science Foundation Division of Materials Research, U.S. Army Research Office, and Office of Naval Research.
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