Papers by Keyword: Graintracking

Abstract: Grain tracking is a term used to describe experiments that investigate polycrystalline materials in terms of the crystallites or grains from which they are composed, non-destructively and in three dimensions. The new German high brilliance synchrotron radiation source, Petra III, will become available to users in 2010 [1]. The GKSS research centre will operate two beamlines, including the high energy materials science beamline (HEMS) [2]. HEMS will feature an instrument dedicated to grain tracking, able to support a range of experiments of this kind. This paper describes the design and specification of this instrument, and gives examples of the types of experiments that will be possible.

Abstract: In this paper the authors describe a technique based on synchrotron x-ray diffraction which has been used to produce full 3D grain maps (both grain shapes and orientations) in annealed aluminium alloy and stainless steel samples containing around 500 grains. The procedure is termed diffraction contrast tomography (DCT), reflecting its similarities with conventional absorption contrast tomography. It is an extension of the 3D X-ray diffraction microscopy (3DXRD) concept, and has been developed in collaboration with its inventors. The specimen is illuminated using a monochromatic synchrotron x-ray beam, and grains imaged using the extinction contrast that appears in the transmitted beam when grains are aligned in the diffraction condition during rotation of the sample. The beams of radiation diffracted by the grains are captured simultaneously on the same detector as the direct beam image. The combination of diffraction and extinction information aids the grain indexing operation, in which pairs of diffraction and extinction images are assigned to grain sets. 3D grain shapes are determined by algebraic reconstruction from the limited number of extinction projections, while crystallographic orientation is found from the diffraction geometry. The non-destructive nature of the technique allows for in-situ studies of mapped samples. Research is in progress to extend the technique to allow the determination of the elastic strain and stress tensors on a grain-by-grain basis.