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HREM imaging of screw dislocation core structures in bcc metals

Published online by Cambridge University Press:  01 February 2011

B.G. Mendis ,
Y. Mishin ,
C.S. Hartley  and
K.J. Hemker
B.G. Mendis
Affiliation:
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218.
Y. Mishin
Affiliation:
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218. School of Computational Sciences, George Mason University, Fairfax, VA 22030–4444.
C.S. Hartley
Affiliation:
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218. Air Force Office of Scientific Research, Arlington, VA 22203–1954.
K.J. Hemker
Affiliation:
Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218.
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Abstract

Quantitative High Resolution Electron Microscopy (HREM) is used to characterize the in-plane displacements of atoms around a screw dislocation core in bcc molybdenum. The in-plane displacements have an important effect on the bulk mechanical properties of bcc metals and alloys. However, the largest displacements are predicted to be less than 10 pm, requiring that the atom positions in an HREM image be determined to sub-pixel accuracy. In order to calculate the displacements the positions of the atom columns in the undistorted crystal must be determined precisely from the information available in the HREM image. An algorithm for such a task is briefly discussed and the technique applied to several HREM images. It is seen that the atomic displacements are predominantly due to surface relaxation (i.e. Eshelby twist) of a thin TEM foil, thereby masking the finer displacements of the dislocation core. Nye tensor plots, which map the resultant Burgers vector at each point of a distorted crystal, are also used to characterize the core structure. Although the large displacements from the Eshelby twist were completely removed, no signal from the dislocation core region was observed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 839: Symposium P – Electron Microscopy of Molecular and Atom-Scale Mechanical Behavior, Chemistry, and Structure , 2004 , P3.13
Copyright
Copyright © Materials Research Society 2004

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References

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