Browsing by Author "Wcislak, L."

An instrument for diffraction texture measurements in polycrystalline bulk materials using hard X-ray photons from the wiggler beamline BW5 at HASYLAB is described. High-energy photons in the 100 keV regime enable high penetration power in medium-to-high Z materials and the use of Laue diffraction geometry in combination with a two-dimensional area detector allows fast and convenient data collection. Determination of quantitative, high-resolution pole figures with a better angular resolution of 0.1 degrees is attained by the instrument, Profile analysis of the diffraction pattern parameters for each (h k l)-reflection thus provides. in addition to texture data., information about other microstructural quantities, e.g. lattice strain. (C) 2001 Published by Elsevier Science B.V.

In order to describe texture and microstructure of a polycrystalline material completely, crystal orientation g={?1F?2} must be known in all points x={x1?x2?x3} of the material. This can be achieved by locationresolved diffraction of high-energy, i.e. short-wave, X-rays from synchrotron sources. Highest resolution in the orientation- as well as the location-coordinates can be achieved by three variants of a detector sweeping technique in which an area detector is continuously moved during exposure. This technique results in two-dimensionally continuous images which are sections and projections of the six-dimensional orientation location space. Further evaluation of these images depends on whether individual grains are resolved in them or not. Because of the high penetration depth of high-energy synchrotron radiation in matter, this technique is also, and particularly, suitable for the investigation of the interior of big samples.

The orientation distribution of crystallites in polycrystalline materials (called texture) is usually measured by polycrystal X-ray diffraction by "step-scanning" the sample in angular intervals in the order of 1degrees. This technique is not suited to fully exploit the low angular divergence of hard synchrotron radiation in the order of "milliradian". Hence, step-scanning was replaced by a continuous "sweeping" technique using a continuously shifted area detector. In order to. avoid overlapping from different reflections (hkl) a Bragg-angle slit was introduced. The "moving-detector" technique can be applied to obtain images of orientation as well as of location distributions of crystallites in polycrystalline samples. It is suitable for imaging continuous "orientation density" distribution functions as well as of "grain-resolved" textures. The excellent features of high-energy synchrotron radiation combined with the moving area detector technique will be illustrated with several examples including very sharp deformation textures, fully and partially recrystallized samples and materials with steep texture gradients. (C) 2002 Published by Elsevier Science B.V.

The orientation distribution of the Widmannstatten plates was measured in a sample of the Gibeon iron-nickel meteorite. The measurements were made with high-energy synchrotron radiation at beamline BW5 at HASYLAB/DESY in Hamburg using a high-resolution 'moving-detector' technique. The measurements reveal a continuous range of orientations stretching out from both sides of the Nishiyama-Wassermann orientation to the Kurdjumov-Sachs orientations, as well as a minor 'spread-pipe' between the Kurdjumov-Sachs ends of neighbouring non-coplanar orientation variants.

The x-ray diffraction instrument at the HASYLAB high-energy wiggler beamline BW5 in Hamburg was set-up for diffraction experiments with wavelengths in the range of 0.1Angstrom. It can be particularly configurated for texture and/or other microstructure investigations in polycrystalline materials of any kind. The performance of the whole equipment was checked with random samples on the one hand and monocrystals on the other as well as for various textured materials. A software system leading from the experimental diffraction data to pole figures and to ODF, particularly designed to the specifications of BW5, was developed and installed. The experimental set up and the software system for quantitative texture analysis are available for external users.

Texture measurement with short-wave X-ray synchrotron radiation in the range of lambda similar or equal to 0.1 Angstrom is described. The measurements were carried out with the multipurpose diffraction instrument at the high-field wiggler, high-energy beamline BW5 at HASYLAB. The instrument was equipped with an on-line image-plate area detector for diffraction-image registration and a Eulerian cradle for sample orientation. The particular features of texture measurement with the BW5 instrument are: good resolution in the Bragg angle, extremely high angular resolution in crystal orientation (pole-figure angles) and particularly high penetration depth of several millimetres to centimetres, comparable with that of neutrons but at high spatial resolution. Several examples illustrate the particular advantages of this method for texture studies using large or encased samples (in situ studies in complicated environments, such as cryostats, furnaces, vacuum or pressure chambers, with no serious window problems). This allows, among others, non-destructive texture analysis in technological parts and whole components. Because of the extremely high beam intensity (short exposure times) compared with all other methods of texture measurement, the new technique is particularly suited for the study of large sample series (as is often necessary in industrial applications).

High-energy synchrotron radiation with wavelengths in the order of 0.1 Angstrom is used for texture and microstructure analysis of polycrystalline materials. By the conventional step-scan method, pole figures can be measured from which ODF with high angular resolution can be obtained. Additionally a continuous "sweeping" technique is used by which orientation as well as location maps are obtained. This technique is particularly suited to image continuous textures with sharp spatial gradients as well as grain-resolved textures. In this latter case the six-dimensional orientation stereology, comprising texture as well as microstructure, can be obtained. Because of its high penetration depths, comparable with that of neutrons, short-wave synchrotron radiation is particularly suited to study the interior of big samples.

The texture of a material can be calculated from several pole figures, which, in turn, are usually measured by one of several 'step-scan' techniques. In these techniques, the finite step width limits the attainable orientation resolving power. In the present paper, the discontinuous step-scan technique is replaced by a continuous 'sweeping' technique based on the continuous movement of an area detector during exposure. In this way, continuous two-dimensional 'images' of pole figures are obtained, without the necessity of interpolation. Similar sweeping techniques are also being used to obtain continuous images of other sections and projections of the six-dimensional 'orientation - location' space which characterizes a polycrystalline structure completely. The high potential orientation and/or location resolving power of these imaging techniques can only be reached with synchrotron radiation. In the present paper, the measurements were made at the high-energy (short-wavelength) beamline BW5 at HASYLAB/DESY in Hamburg. The high orientation and location resolving power implies the necessity to distinguish 'grain-resolved' textures and microstructures ( mainly in recrystallized materials) from 'continuous' ones ( mainly in deformed materials). Under certain conditions, it is thus possible to obtain the complete six-dimensional 'orientation stereology' of grain-resolved microstructures. The new methods are illustrated with several examples, including technological applications.