Papers by Keyword: 3DXRD

Abstract: The grain-resolved residual stress (type II) in commercial-quality low carbon steel was observed using scanning three-dimensional X-ray diffraction (3DXRD) microscopy. In this method, grain orientations and lattice parameters are mapped using a monochromatic high-energy X-ray microbeam and 3DXRD-based polycrystalline indexing. Defining the reference lattice parameter a₀ as the average value in the entire field of view, grain orientations and lattice parameters are converted into stress tensors, yielding a grain-resolved stress tensor map. The effectiveness of the scanning 3DXRD method was demonstrated by evaluating the residual stress in a cold-rolled low carbon steel sheet using a 50 keV microbeam at SPring-8. The area of the cross-sectional sample was 1×1 mm², which was sufficiently larger than the grain size of about 20 μm. To produce a two-dimensional map of a circular region with a diameter of 160 μm at a pixel size of 1×1 μm², the measurement time was about 1 h. From the stress tensor map, differences in residual stress of about 150–200 MPa between some neighboring grains were observed.

Abstract: New in-situ 3DXRD results obtained since the last Rex&GG conference are presented and discussed. This includes: Documentation of the formation of nuclei with new orientations, determination of apparent activation energies for individual bulk grains during recrystallization and evolution in the 3D microstructure during grain growth.

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: An algorithm is presented for characterization of the grain resolved (type II) stress states in a polycrystalline sample based on monochromatic X-ray diffraction data. The algorithm is a robust 12-parameter-per-grain fit of the centre-of-mass grain positions, orientations and stress tensors including error estimation and outlier rejection. As examples of use results from two experiments – one on interstitial free (IF) steel and one on copper – will be presented. In the first experiment 96 grains in one layer of IF steel were monitored during elastic loading and unloading. Very consistent results were obtained, with resolutions for each grain of approximately 10 μm in position, 0.05˚ in orientation and 80 μstrain. When averaging over all grains a resolution of 10 μstrain was obtained. In the second experiment it was demonstrated that the strain states of more than 1000 grains in a plastically deformed Cu specimen could be determined to an accuracy of 100 μstrain.

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.

Abstract: Grain structures in polycrystalline materials are typically three dimensional (3D) structures, but by far the most characterizations of grain structures are done by microscopy and are thus limited to 2D. In the present work 3D grain structures in a well-annealed cylindrical aluminium (AA1050) sample is characterized and analyzed. The characterization is done by 2 methods i) by non-destructive 3-dimensional x-ray diffraction (3DXRD) ii) by serial sectioning and subsequent EBSP mapping of entire circular 2D sample sections; 50 sections are mapped In total 333 grains are reconstructed. It is found that the 3D grain morphologies can be quite complex in particular for the larger grains, the number of neighbours varies significantly and values above 20 are not unusual. When the results from the 2 methods are compared, it is found that the crystallographic agreement is very good and within experimental uncertainties. Slightly more significant differences are found when the reconstructed grain morphologies are compared. Reasons for this are discussed.

Abstract: A partially recrystallised sample has been characterised by 3DXRD. A gauge volume of 200μm × 700μm × 300μm has been fully mapped. Deformed and recrystallised regions within the selected gauge volume are distinguished based on the sharpness of the diffraction spots. Information corresponding to a 5D (Φ1, Φ, Φ2, z, x · y) map is deducted from the 3DXRD data.

Abstract: Effects of the crystallographic misorientation across boundaries between recrystallising grains and the neighbouring deformed matrices are discussed and exemplified by recrystallisation investigations of fcc metals. Classic misorientation observations are reviewed in the introduction, whereas the main parts of the paper focuses on two special boundary migration phenomena observed by in-situ recrystallisation experiments; namely protrusions and facets.

Abstract: The deformation behavior of metastable austenitic stainless steel AISI 301, suffering different initial cold rolling reduction, has been investigated during uniaxial tensile loading. In situ highenergy x-ray diffraction was employed to characterize the residual strain evolution and the strain induced martensitic transformation. Moreover, the 3DXRD technique was employed to characterize the deformation behavior of individual austenite grains during elastic and early plastic deformation. The cold rolling reduction was found to induce compressive residual strains in the austenite along rolling direction and balancing tensile residual strains in the ά-martensite. The opposite residual strain state was found in the transverse direction. The residual strain states of five individual austenite grains in the bulk of a sample suffering 2% cold rolling reduction was found to be divergent. The difference among the grains, considering both the residual strains and the evolution of these, could not be solely explained by elastic and plastic anisotropy. The strain states of the five austenite grains are also a consequence of the local neighborhood.

Abstract: By 3 dimensional X-ray diffraction (3DXRD) using high energy X-rays from synchrotron sources it is possible to study in-situ the nucleation and growth during recrystallization. In this paper it is described and discussed how 3DXRD can supplement EBSP measurements of nucleation and growth. Three types of studies are considered: i) orientation relationships between nuclei and parent deformed matrix, ii) recrystallization kinetics of individual bulk grains and iii) filming of growing grains in deformed single crystals.