THREE-DIMENSIONAL EVALUATION OF DISLOCATION ARRANGEMENTS USING ELECTRON TOMOGRAPHY IN AUSTENITIC STEEL

In order to comprehend three-dimensional (3D) dislocation arrangements in deformed austenitic steels, we firstly investigated appropriate imaging conditions for electron tomography with scanning transmission electron microscopy (STEM). Dislocation contrast is clearly observed in a bright-field (BF) STEM images due to lowering of dynamical diffraction contrast, such as thickness fringes and bend contours. The high dislocation contrast was maintained at a high specimen-tilt angle. Next, we attempted a 3D reconstruction using two BF-STEM tilt-series to avoid extinction of the dislocation lines. In the resultant 3D microstructure, the dislocation arrangements were clearly observed at an arbitrary orientation. The length and density of dislocations in the whole reconstructed space are 907 mu m and 3.8 x10(13) m(-2), respectively. In addition, it was demonstrated that the dislocation density gradually decreased near free surface.