Image contrast of dislocating loops in anisotropic cubic crystals
A computer program to generate simulated electron micrographs has been used to calculate the image contrast of dislocation loops in cubic crystals by taking into account the effect of elastic anisotropy. The displacement field was numerically calculated for a circular dislocation loop of finite size from the Fourier transform of the elastic Green's function. The image contrast was calculated under two-beam dynamical diffraction conditions using the Howie-Whelan equations. In an isotropic medium, the black-white contrast direction of a Frank loop imaged under the exact (002) Bragg reflection makes an angle of approximately 15/sup 0/ from the direction of Burgers vector. In copper and nickel, the anisotropic calculations show that the black-white contrast is parallel to and is elongated considerably along the direction of the Burgers vector. In niobium, the black-white contrast direction of a perfect loop of a/2(111) type lies about halfway between the directions of the Burgers vector and the diffraction vector. It is concluded that the image contrast of dislocation loops in cubic crystals is highly sensitive to the elastic anisotropy and hence it is necessary to take the effect of anisotropy into account in order to perform an accurate analysis of the loop image.
- Research Organization:
- Oak Ridge National Lab., TN (USA)
- DOE Contract Number:
- W-7405-ENG-26
- OSTI ID:
- 6629495
- Report Number(s):
- CONF-780818-7
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360102* -- Metals & Alloys-- Structure & Phase Studies
COPPER
CRYSTAL DEFECTS
CRYSTAL LATTICES
CRYSTAL STRUCTURE
CRYSTALS
DISLOCATIONS
ELECTRON MICROSCOPY
ELEMENTS
FOURIER TRANSFORMATION
FUNCTIONS
GREEN FUNCTION
IMAGE PROCESSING
IMAGES
INTEGRAL TRANSFORMATIONS
LINE DEFECTS
METALS
MICROSCOPY
MONOCRYSTALS
NICKEL
NIOBIUM
REFRACTORY METALS
SIMULATION
TRANSFORMATIONS
TRANSITION ELEMENTS