Fundamental Understanding of Superplasticity in Nanocrystalline Metals

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9630881 Mukherjee This grant provides fundamental understanding of superplastic behavior in nanocrystalline materials. Ultrafine-grained nanocrystalline materials contain a very large density of interfaces and, therefore, offer unique opportunities for studying the structural state of grain boundaries and their role on grain boundary sliding during superplasticity. Combining methods for synthesis as well as consolidation of nanopowders, the experimental program examines superplastic deformation behavior of nanometals, nanointermetallics, and nanocomposites with nanoscale oxides dispersed in the nanoscale metallic matrix. The scientific goal is to correlate in the context of theoretical models of superplasticity new microstructural information with mechanical data obtained from nanoscale materials. Special emphasis is given to the difficulty of intragranular dislocation generation inside the matrix in truly nanoscale structure and its consequences to slip accommodation in current models of superplasticity. The nanostructure before and after deformation is investigated using transmission electron microscopy, X-ray diffraction and internal friction methods. %%% The research could lead to new processing techniques for deformation processing of nanocrystalline materials and could impact future metal alloy processing in the metal forming industries. ***