期刊
ACTA MATERIALIA
卷 56, 期 14, 页码 3663-3671出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2008.04.003
关键词
nanocrystalline; theoretical density; excess volume; dislocation density; grain size
资金
- Los Alamos National Laboratory
- US Department of Energy's Office of Basic Energy Sciences
- DOE [DE-AC52-06NA25396]
We prepared nanocrystalline Ni by a severe deformation method - high-energy ball milling - and collected neutron diffraction patterns during the annealing of nanocrystalline Ni. Analyzing the neutron diffraction patterns provides the lattice parameter, dislocation density and grain size of nanocrystalline Ni. We found that a low-temperature (T < 260 degrees C) anneal annihilates the statistically stored dislocations whereas a high-temperature (T > 260 degrees C) anneal grows the nanograins. For T < 260 degrees C. where nanocrystalline Ni has a constant grain size, the excess volume is proportional to the density of statistically stored dislocations. For T > 260 degrees C, where the statistically stored dislocations are completely annealed out, the excess volume is inversely proportional to the grain size. However, 80% of the excess volume in our severely deformed nanocrystalline Ni is due to the statistically stored dislocations. We finally used our experimental data to derive the grain size dependence of the theoretical density of a nanocrystalline material free from excess dislocations. The derived theoretical density agrees well with the experimentally measured density of nanocrystalline metallic materials that are relatively free from deformation-induced defects. Published by Elsevier Ltd on behalf of Acta Materialia Inc.
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