High-resolution TEM Analysis of Defect Structures in Mechanically Milled, Nanocrystalline Fe

Grain interior and grain-boundary structures of mechanically milled ultrafine-grained iron powder were investigated with atomic resolution using high-resolution transmission electron microscopy (HRTEM). Grain boundaries in the powder appear wavy and irregular, with no amorphous or other unusual defe...

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Bibliographic Details
Published in:ISIJ International 2003/05/15, Vol.43(5), pp.755-760
Main Authors: Murayama, M., Howe, J. M., Hidaka, H., Takaki, S.
Format: Article
Language:English
Subjects:
Applied sciences
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
high-resolution transmission electron microscopy
Materials science
Materials synthesis
materials processing
mechanically milled iron
Metals. Metallurgy
nanostructure
Physics
Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
ultrafine-grained material
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Summary:Grain interior and grain-boundary structures of mechanically milled ultrafine-grained iron powder were investigated with atomic resolution using high-resolution transmission electron microscopy (HRTEM). Grain boundaries in the powder appear wavy and irregular, with no amorphous or other unusual defect structures present. Diffraction analysis of HRTEM images indicates that elongated grains approximately 100 nm long and 20 nm wide consist of several sub-grains along their length, each rotated by several degrees around a common ‹110› axis. The presence of partial disclination dipoles in the sub-grains was also observed by HRTEM. Such structures indicate that shear, fragmentation and rotation of grains several to tens of nanometers in diameter occurs during severe plastic deformation. A mechanism for the formation of an ultrafine-grained structure in mechanically milled Fe involving partial disclinations is proposed.
ISSN:0915-1559
1347-5460
DOI:10.2355/isijinternational.43.755