Papers by Keyword: Diffraction Contrast Tomography

Abstract: The formability of Aluminum 2050 alloy is critical for manufacturing large and thick components while maintaining its outstanding performance. To link the damage development during high-temperature loading with the alloy microstructure evolution, a time resolved tensile loading experiment at 480 °C was performed on this alloy using synchrotron diffraction and tomography, i.e. diffraction contrast tomography (DCT) to provide 3D grain maps and phase contrast tomography (PCT) to characterize pores and intermetallics. The evolution of both was quantified as a function of macroscopic strain up to 20.15%. Three pore formation mechanisms were identified: growth from pre-existing pores, fracture of the intermetallics, and nucleation of new pores. The characteristics of the pore evolution are linked with the grain structure characterized by DCT. Additionally, the grain maps reconstructed for initial and final strained states show newly recrystallized grains, indicating the presence of dynamic recrystallization. To exclude the possible explanation by annealing recrystallization, an extra annealing experiment was performed and no recrystallized grains were observed. A comprehensive insight into linking the damage development with the microstructure evolution under high-temperature deformation has been obtained by using synchrotron grain mapping techniques and tomography.

Abstract: Diffraction contrast tomography using ultrabright synchrotron radiation X-rays was performed on an austenitic stainless steel with a bimodal harmonic structure in which a network structure of fine grains (Shell) surrounds a coarse grain structure (Core). Then, not only were the shape and position of each grain reconstructed, but the change in excess dislocation density during the fatigue process, Δρ, was also measured. The results show that Δρ depends on the diffraction plane, Schmidt factor, and grain size, and that the change in Δρ during the fatigue process of a harmonic structured material is less than that of a conventional material. This result indicates that the network of fine grains in the harmonic structure supports microdeformation and suppresses the deformation of coarse grains. Furthermore, it was found that Δρ of grains unrelated to crack initiation increased continuously with the number of cycles, whereas that around the crack initiation site decreased with crack initiation.

Abstract: A three dimensional grain mapping technique for polycrystalline materials, called X-ray diffraction contrast tomography (DCT), was developed at SPring-8, which is the brightest synchrotron radiation facility in Japan. The developed technique was applied to a commercially pure iron and austenitic stainless steel. The shape and location of grains could be determined by DCT using the apparatus in a beam line of SPring-8. To evaluate the dislocation structure in fatigue, the total misorientation of individual grains was measured by DCT. The average value of the total misorientation over one sample was increased with the number of cycles. In a grain, the change of the total misorientation was largest for primary slip plane. For austenitic stainless steel (fcc), the change of the total misorientation in fatigue was larger for planes with larger Schmid factor, while it was not depended on the Schmid factor for commercially pure iron (bcc). This different behavior must come from planer slip in fcc structure and wavy slip in bcc structure.

Abstract: The three dimensional grain mapping technique for polycrystalline material, which is called X-ray diffraction contrast tomography (DCT) has proposed. In the present study, the measurement of DCT was conducted in SPring-8, which is the brightest synchrotron radiation facility in Japan, and the condition of measurement and data procedure are discussed. Developed technique was applied to aluminium alloy and stainless steel. The shape and location of grain could be determined by the developed three-dimensional mapping technique using the apparatus in a bending beam line of SPring-8. To evaluate plastic deformation, the grain orientation spreads of individual grains were measured. The grain orientation spread is caused by the mosaicity, which relates to the dislocation structure in a grain. The grain orientation spread was found to increase with increasing plastic strain. Fatigue damage also could be evaluated by the grain orientation spread in the DCT measurement.

Abstract: The three dimensional grain mapping technique for polycrystalline material, which is called X-ray diffraction contrast tomography (DCT) has proposed. In the present study, the measurement of DCT was conducted in SPring-8, which is the brightest synchrotron radiation facility in Japan, and the condition of measurement and data procedure are discussed. Developed technique was applied to aluminium alloy and stainless steel. The shape and location of grain could be determined by the developed three-dimensional mapping technique using the apparatus in a bending beam line of SPring-8. To evaluate plastic deformation, the grain orientation spreads of individual grains were measured. The grain orientation spread is caused by the mosaicity, which relates to the dislocation structure in a grain. The grain orientation spread was found to increase with increasing plastic strain. Fatigue damage also could be evaluated by the grain orientation spread in the DCT measurement.

Abstract: A 3D model for intergranular thermal stresses in coarse polycrystalline alumina has been derived using Diffraction Contrast Tomography. Larger tensile thermal strains develop when the (0001) pole of adjacent grains lies closer to the grain boundary normal. This agrees with observations of cracked boundaries, obtained through digital image correlation of in-situ observations in fine alumina.

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.