Papers by Keyword: Convergent Beam Electron Diffraction (CBED)

Abstract: Orientation mapping in transmission electron microscope was successfully applied to study microstructural changes at the initial stage of recrystallization in the aluminum alloy with a bimodal second-phase particle distribution. The alloy samples were reversibly cold rolled resulting in the formation of laminar structure with zones of localized strain around large second-phase particles. Orientation mapping and in-situ investigations carry information about the processes which are active in the deformation zones during annealing.

Abstract: The ambiguity in determination of complete elastic strain tensor by convergent beam electron diffraction can be overcome by simultaneous use of multiple diffraction patterns. Numerical tests of strain determining procedure based on multiple patterns have been carried out. Patterns were simulated using both kinematic and dynamic approaches, and then they were used as input in the tested procedure. The tests indicate that, in practice, at least three patterns are needed in order to determine a complete strain tensor with reasonable accuracy. The strain resolution of two parts per ten thousand was achieved with five diffraction patterns. Moreover, the impact of errors in voltage and camera length is considered. It is shown that within the kinematic description, the deviations from the correct voltage are equivalent to errors in the isotropic part of strain.

Abstract: Internal stress field in a severely deformed aluminium with ultrafine grained microstructure has been studied by convergent-beam electron diffraction (CBED) technique in transmission electron microscopy (TEM). A commercial purity aluminium (99.1%Al) sheet was highly strained by the accumulative roll-bonding (ARB) process to evolve an ultrafine grained structure. Higher-order Laue zone (HOLZ) lines in the incidence disk of the ] 12 1 [ zone axis have been observed at various positions within an identical ultrafine grain. The key finding is that the HOLZ line pattern taken from the vicinity (~50nm) of the grain boundary (lamellar boundary) looses ) 1 1 0 ( mirror symmetry, whereas the pattern from the grain centre has the symmetry. The former and the latter represent the existence of a large non-hydrostatic stress field and a small internal stress field, respectively. The magnitude of the internal stress becomes larger with approaching to a grain boundary.