Papers by Henning Poulsen
Acta Materialia, 2003
Three-dimensional X-ray diffraction has been applied to characterise the plastic deformation of i... more Three-dimensional X-ray diffraction has been applied to characterise the plastic deformation of individual grains deeply embedded in a 99.6% pure aluminium specimen. The specimen is 4 mm thick with an average grain size of 75 µm. The average lattice rotation for each grain as well as the degree of internal orientation spread within the grain is measured in-situ during 6% elongation. The rotation paths for 95 grains with nearly random initial orientations are reported. The quality of this data set is sufficient to make distinctions between plasticity models. The rotation paths exhibit a clear dependence on the initial orientation, while the influence of grain interaction is relatively small. All grains deform plastically. Averaged over grains and reflections the rotation of the tensile axis and the FWHM of the internal spread is 2.0 and 0.8°, respectively, at 6% strain.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2006
The three-dimensional X-ray diffraction (3DXRD) microscope has become a mature tool to investigat... more The three-dimensional X-ray diffraction (3DXRD) microscope has become a mature tool to investigate the microstructure in the bulk of polycrystalline materials. The present paper describes the 3DXRD method together with two applications. The first application presented is a study of grain rotations during plastic tensile deformation of polycrystalline aluminium. The second is the acquisition of a video revealing the 3D growth of an embedded nuclei during recrystallization of a deformed aluminium sample.
Combining 3DXRD and Absorption Contrast Tomography
Springer Tracts in Modern Physics, 2004
ABSTRACT The 3DXRD setup sketched in Fig. 3.1 is very similar to the setup typically used for abs... more ABSTRACT The 3DXRD setup sketched in Fig. 3.1 is very similar to the setup typically used for absorption contrast x-ray tomography at synchrotrons. Furthermore it appears that the specifications of the two methods in terms of space and time resolution are not very different (see Table 6.1). Hence, combined studies can be envisioned. With suitable detector combinations, one might even probe the same specimen with both techniques simultaneously. ...
The 3DXRD Microscope
Springer Tracts in Modern Physics, 2004
ABSTRACT The 3DXRD microscope at ESRF is installed in a separate laboratory, the second experimen... more ABSTRACT The 3DXRD microscope at ESRF is installed in a separate laboratory, the second experimental hutch at beamline ID11 [1,2]. The beamline is an insertion device beamline equipped with an in-vacuum undulator with a minimum gap of 5 mm. The beam enters the experimental hutch through a pinhole with fixed dimensions of 1 × 1 mm 2. The photon flux at the point of entry is shown as a function of x-ray energy in Fig. 2.4. The design of the microscope is sketched in Fig. 8.1. It comprises x-ray optics, contained within Pb shielding, and a diffractometer. Adjacent to the experimental hutch, there is a control room. ...
GRAINDEX and Related Analysis
Springer Tracts in Modern Physics, 2004
ABSTRACT
Electrical and magnetic properties of Nb sub 2 O sub 5 minus. delta. crystallographic shear structures
Physical review. B, Condensed matter
The reduced niobium oxides NbââOââ, NbââOâââ, NbââOââ, and NbââOââ have been prepared in pure ... more The reduced niobium oxides NbââOââ, NbââOâââ, NbââOââ, and NbââOââ have been prepared in pure polycrystalline form by a niobium-metal gettering technique. They are related to the high niobia parent structure through the action of cystallographic shear to accommodate oxygen deficiency in NbâO{sub 5-δ}. Electrical conductivities increase with increasing reduction: NbââOââ is a metallic conductor down to 0.3 K. All show, surprisingly, Curie-Weiss behavior in the Ï-vs-{ital T} curves, with NbââOââ ordering antiferromagnetically at 12 K.
Relation between superconducting transition temperature and oxygen ordering in YBa2Cu3O(6+x)
Nature
ABSTRACT
Growth kinetics of individual cube grains as studied by the 3D X-ray diffraction microscope
Diffraction of high-energy synchrotron radiation (invited) (abstract)
Review of Scientific Instruments, 1995
Diffraction of high-energy synchrotron radiation at energies above 100 keV combines advantages of... more Diffraction of high-energy synchrotron radiation at energies above 100 keV combines advantages of conventional x-ray diffraction and neutron diffraction. For hard x rays absorption in matter is weak with typical mean free paths of several millimeters. Bulk properties are studied on large samples. With a three-crystal diffractometer an excellent k-space resolution of about 10−5 A˚−1 transversal and 10−4 A˚−1 longitudinal
Transmission electron microscopy investigation of Bi2223/Ag tapes
Physica C-superconductivity and Its Applications, 2001
The microstructure of (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) tapes has been investigated by means of trans... more The microstructure of (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) tapes has been investigated by means of transmission electron microscopy (TEM) and high-resolution TEM. The emphasis has been placed on: (1) an examination of the grain morphology and size, (2) grain and colony boundary angles, which are formed during the tape processing, (3) a study of the grain boundaries on an atomic scale, including intergrowth
Direct Observation of Grain Boundary Wetting by Synchrotron Radiation Imaging Techniques
Defect and Diffusion Forum, 2001
... Acta mater., 48:3303-3310, 2000. [5] RC Hugo and RG Hoagland. ... Principles of Computerized ... more ... Acta mater., 48:3303-3310, 2000. [5] RC Hugo and RG Hoagland. ... Principles of Computerized Tomographic Imaging. IEEE Press, New York, 1988. 15] HF Poulsen, SF Nielsen, EM Lauridsen, U. Lienert, and RM Suter and D. Juul Jensen. Submitted, 2000. ...
Electrical and magnetic properties of Nb2O5- delta crystallographic shear structures
Physical review. B, Condensed matter, 1991
The reduced niobium oxides Nb25O62, Nb47O116, Nb22O54, and Nb12O29 have been prepared in pure pol... more The reduced niobium oxides Nb25O62, Nb47O116, Nb22O54, and Nb12O29 have been prepared in pure polycrystalline form by a niobium-metal gettering technique. They are related to the high niobia parent structure through the action of cystallographic shear to accommodate oxygen deficiency in Nb2O5-delta. Electrical conductivities increase with increasing reduction: Nb12O29 is a metallic conductor down to 0.3 K. All show, surprisingly,
Materials Science Forum, 2007
The implementation of 3-Dimensional X-Ray Diffraction (3DXRD) Microscopy at the Advanced Photon S... more The implementation of 3-Dimensional X-Ray Diffraction (3DXRD) Microscopy at the Advanced Photon Source is described. The technique enables the non-destructive structural characterization of polycrystalline bulk materials and is therefore suitable for in situ studies during thermo-mechanical processing. High energy synchrotron radiation and area detectors are employed. First, a forward modeling approach for the reconstruction of grain boundaries from high resolution diffraction images is described. Second, a high resolution reciprocal space mapping technique of individual grains is presented.
A Depth-Resolved In-Situ Study of the Reduction and Oxidation of Ni-Based Anodes in Solid Oxide Fuel Cells
ABSTRACT The stability of Ni-YSZ anodes as part of solid oxide fuel cells (SOFCs) towards redox c... more ABSTRACT The stability of Ni-YSZ anodes as part of solid oxide fuel cells (SOFCs) towards redox cycling is an important issue for successfully introducing the technology. Detailed knowledge of the NiO-Ni transitions and their impact on the mechanical integrity of the whole system is necessary to improve the overall stability. In the present paper, a unique in-situ X-ray diffraction setup is presented which allows monitoring of the local structural changes during processing of SOFCs. With this setup technological SOFCs – a half cell and a full cell – were studied with respect to NiO-Ni transitions in repeated reduction-oxidation cycles, under conditions relevant for SOFC application. It was found that the redox kinetics is a function of the sample depth. Ni particles further away from the surface were reduced/oxidized at a slower rate than particles close to the surface.
Applied and Numerical Harmonic Analysis, 2007
The determination of crystalline structures is a demanding and fundamental task of crystallograph... more The determination of crystalline structures is a demanding and fundamental task of crystallography. Most crystalline materials, natural or artificial, are in fact polycrystals, composed of tiny crystals called grains. Every grain has an associated average orientation that determines the spatial configuration of the crystalline lattice. Typically, the structure of a polycrystal is rendered via an orientation map or a grain map, in which individual pixels/voxels are assigned a grain orientation or a grain label. We present two related approaches to reconstructing a 2D grain map of a polycrystal from X-ray diffraction patterns. The first technique makes the assumption that each grain is actually a perfect crystal, i.e., that the specimen is not deformed. The other method can be applied also when the sample has been exposed to moderate levels of deformation. In both cases, the grain map is produced by a Bayesian discrete tomographic algorithm that uses Gibbs priors. The optimization of the objective function is accomplished via the Metropolis algorithm. The efficacy of the techniques is demonstrated by simulation experiments.
In-Situ Observation of Subgrain Evolution during Static Recovery of Cold-Rolled Aluminium
Materials Science Forum, 2004
3DXRD – Mapping Grains and Their Dynamics in 3 Dimensions
Materials Science Forum, 2004
ABSTRACT
SIAM Journal on Imaging Sciences, 2009
A fundamental imaging problem in microstructural analysis of metals is the reconstruction of loca... more A fundamental imaging problem in microstructural analysis of metals is the reconstruction of local crystallographic orientations from X-ray diffraction measurements. This work develops a fast, accurate, and robust method for the computation of the three-dimensional orientation distribution function for individual grains of the material in consideration. We study two iterative large-scale reconstruction algorithms, the algebraic reconstruction technique (ART) and conjugate gradients for least squares (CGLS), and demonstrate that right preconditioning is necessary in both algorithms to provide satisfactory reconstructions. Our right preconditioner is not a traditional one that accelerates convergence; its purpose is to modify the smoothness properties of the reconstruction. We also show that a new stopping criterion, based on the information available in the residual vector, provides a robust choice of the number of iterations for these preconditioned methods.
Acta Materialia, 2003
A universal method is presented for characterising the three-dimensional (3D) plastic displacemen... more A universal method is presented for characterising the three-dimensional (3D) plastic displacement gradient field in bulk materials that contain particles or voids observable by X-ray tomography. Millimetre sized samples are investigated by absorption contrast microtomography using high intensity X-rays from a synchrotron source. The positions of dispersed marker particles are determined as a function of imposed strain. The particle diameter
Ferrite Formation during Slow Continuous Cooling in Steel
Materials Science Forum, 2007
1 Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 26... more 1 Department of Materials Science and Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. 2 Department of Materials Science and Engineering, Royal Institute of Technology, S-100 44 Stockholm, Sweden. 3 Department of Radiation, ...
Uploads
Papers by Henning Poulsen