Journal
ACTA MATERIALIA
Volume 53, Issue 10, Pages 3031-3040Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2005.03.016
Keywords
severe plastic deformation; transmission electron microscopy; nickel aluminide; nanostructure; geometrically necessary dislocations
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The evolution of a nanocrystalline structure of a polycrystalline L1(2) ordered Ni3Al alloy was investigated by transmission electron microscopy methods after severe plastic deformation by high pressure torsion. As a precursor of the nanocrystalline structure, blocks and bands are formed containing misoriented fragments in the 100 nm range separated by a three-dimensional array of low angle boundaries. The inhomogeneous deformation leads to localized disorder and a high density of dislocations, especially geometrically necessary ones. Dynamic recovery causes a heterogeneous formation of the nanocrystalline structure. The interplay of dynamic recovery and disordering yields nanograins in the disordered state. At strains of about 8000% a duplex structure is formed consisting of veins of disordered nanograins that are embedded in the ordered coarse-grained structure. The nanocrystalline veins showing a weak texture grow by the formation of nanograins generated autocatalytically at their interface. Finally, at strains above 50,000% the whole volume transforms to the nanocrystalline structure. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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