Texturescope: An automatic TEM technique for the imaging of preferred orientations

Abstract

The distribution of crystallographic orientations, the texture, is one of the basic structural parameters. Knowledge of the texture on a very local scale is necessary to study aspects of processes such as recrystallization and deformation. With an electron microscope, the texture can be determined1 either by measuring the orientations of individual grains or by measuring local pole figures and obtaining in this way the orientation distribution of hundreds of grains. The latter method, however, does not preserve the spatial distribution of the orientations.The measurement of pole figures in the TEM is based on the same principles used for conventional pole figure determination by X-rays in transmission. The electron microscope has the additional capability that the area of interest can be imaged. For the measurement of local pole figures, the intensity distribution along a selected hkl-diffraction ring is measured, while the specimen is tilted around a specified axis over a large range (e.g. sheet products are usually tilted around the rolling direction). The measured diffracted intensities must be corrected for absorption of the primary and diffracted beams as well as for the change in diffracting volume. Using selected area diffraction, pole figures of specimen areas between 300 μm and 1 μm in diameter can be analyzed quantitatively.