Abstract
We have studied three-dimensional (3D) configurations of dislocations in the β phase of a Ti–35mass%Nb alloy by means of single-axis tilt tomography using bright-field scanning transmission electron microscopy (BF-STEM). To visualize dislocations, the hh0 systematic reflections were excited throughout tilt-series acquisition with the maximum tilt angle of 70°. Dislocations in the β grains were clearly reconstructed by the weighted back-projection algorithm. The slip planes of the dislocations were deduced by rotating the reconstructed volumes with the aid of selected area electron diffraction patterns. It was found that BF-STEM images with relatively low contrasts, taken along low-order zone axes, are capable to reproduce and preserve the quality of reconstructed image of dislocations. We also found that tilt angles as low as 40° are practically acceptable to visualize 3D configurations of dislocations, while there exists limitation in resolution due to the existence of a large missing wedge.
Highlights
Electron tomography is a technique to visualize three-dimensional (3D) structures inside materials in a transmission electron microscope (TEM) with the aid of computational reconstruction processes.This technique has been applied for various fields of materials science so far [1]
Hh0 systematic reflections are excited along the tilt axis of the triple-axes holder
To check the effect of such Bragg reflections other than the hh0 systematic reflections on the quality of reconstructed dislocation images, we examined 3D reconstruction removing images obtained under low-order zone axes incidence
Summary
Electron tomography is a technique to visualize three-dimensional (3D) structures inside materials in a transmission electron microscope (TEM) with the aid of computational reconstruction processes. This technique has been applied for various fields of materials science so far [1]. Our attempt here is to visualize dislocations in a rather narrow area in two-phase alloys. For this purpose, we selected a quenched Ti–35mass%Nb alloy composed of a so-called α'' martensite with an orthorhombic structure and a small amount of the β phase with a body centered cubic (bcc) structure [11]. It is noted that there is few report on the dislocation tomography of bcc crystals
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