High-Energy X-Rays: A tool for Advanced Bulk Investigations in Materials Science and Physics

The combination of these techniques is a strong issue for the construction and development of future instruments.

Effect of Gravity on the Kinetics of Consolidation of Powder Bodies

Physical mathematical model of sintering powders is suggested with respect to the influence of gravitation on sintering kinetics. Structure genesis and evolution in sintered glass-based particulate bodies is investigated both in computer simulations and “in situ”.

Torsion Texture Measurements With High-Energy Synchrotron Radiation on NiAl

Diffraction with high-energy synchrotron radiation is a new experimental method to determine textures of materials, which due to the special properties of this radiation, in the future may have advantages in terms of accuracy of local texture measurements in comparison to established methods like Electron back scatter diffraction (EBSD). In the present study NiAl polycrystals with two different initial textures have been deformed in torsion at 727°C and 1000°C and their texture development has been measured with highenergy synchrotron radiation. Torsion enables the study of texture formation with strain as well as the exploration of large strains without changing the shape of the samples. The pole figures indicate the preferred alignment of ‹100› with the shear direction and {110} with the shear plane. High pressure torsion may also open new possibilities in terms of grain refinement and texture formation and thus ductilization of NiAl.

Depth Resolved Strain and Phase Mapping of Dissimilar Friction Stir Welds Using High Energy Synchrotron Radiation

The strain and phase distribution in a dissimilar friction stir weld of AA6082-T6 to AA2024-T3 is investigated non-destructively. The measurements are performed using a novel depth resolved strain and phase mapping technique. The technique is based on the use of a focussed high energy synchrotron beam, a novel spiral slit system, and an area detector system. Through thickness measurements of the residual strain along the weld centre show strong variations with changes of sign. The strain scans across the weld exhibit a strong asymmetry in particular for the longitudinal strain component. A depth resolved strain mapping across the weld shows for the dominant longitudinal strain component variations in depth, especially on the AA6082 side of the weld. Results from the strain measurements are related to the depth resolved map of the material distribution in the weld zone.

Hot-Extruded and Cold-Rolled Textures of the Matrix Aluminum in Deformation Processed Two-Phase Nb/Al Metal-Metal Composites

In this article, the powder metallurgy technique combined with flat hot-extrusion and cold rolling processes was employed to fabricate 10 and 20vol.%Nb/Al metal–metal composite sheets. The hot-extruded and coldrolled textures of the matrix aluminum in these metal–metal composite sheets were investigated by three dimensional orientation distribution functions (ODFs) analysis. The results show that the extrusion mode and large second phase particulate metal, Nb, have strong influence on the development of the extrusion and cold rolling textures in composites’ matrix. The matrix Al forms β-fiber textures after flat hot extrusion, where the components consist of B′-{011} ‹322›, S′-{124} ‹654› and C′-{113}h332i. After cold rolling process, only B′-{011} ‹322› changed to B-{011} ‹211› while the other components remained the same. The large particles in composites affect the matrix deformation in such a way that separates the distorted or bound zones from the deformation zones, which resulted in the final cold rolling deformation textures.

Applications on High-Energy X-Rays to Stress Measurements of Thermal Barrier Coatings

High-energy X-rays from a synchrotron radiation source, SPring-8, were applied to the stress measurements of thermal barrier coating (TBC). The specimen had a zirconia top coat on a bond coat of NiCoCrAlY sprayed on the substrate of Ni-base super alloys. The stress in the bond coat was measured through the top coat using the diffraction of Ni3Al 311 by high-energy X-rays with an energy of 72 keV. The sin2ψ method was used to determine the stress value. A specially designed furnace with a wide beryllium window was developed to conduct in-situ measurements of the internal stress in the bond coating at the room temperature, 773, 1073, and 1373 K. The internal stress was tensile at the room temperature, and decreased with increasing temperature. At 1073K or higher, the internal stress in the bond coat was released due to softening of the bond coat. The normal stress perpendicular to the coating surface of TBC was evaluated by a new hybrid method. Since the penetration depth of low-energy X-ray is very small around a few micrometers for zirconia, the stress value measured by the sin2ψ method is the in-plane stress, σ1, and the stress perpendicular to the surface was zero. On the other hand, the penetration depth of high-energy X-rays is very deep, so the measured stress value will be the in-plane stress minus the out-of-plane stress, i.e. σ1−σ3. The normal stress perpendicular to the surface, σ3, i.e. the spalling stress, was estimated from these two measurements. The specimens were exposed in air atmosphere at 1373 K for 500, 1000, and 2000 h. The distribution of the spalling stress in the top coat was estimated by the hybrid method. The spalling stress near the interface to the bond coat changed to a large tension after long-time exposure.

Influence of Grain Number on Graphite Quantitative Texture Study

The present work is devoted to the study of the grain number influence on the quantitative texture analysis and on the values of averaged elastic properties. Number of grains does not influence mathematical definition of orientation distribution function (ODF) (Bunge, H.J. (1982). Texture Analysis in Material Science. Butterworths, London; Matthies, S., Vinel, G.W. and Helming, K. (1987). Standard Distributions in Texture Analysis. Akademie-Verlag, Berlin.); nevertheless, intuitively clear that, averaging procedure implies a ‘‘large’’ number of grains to make sense. In the present work we applied the already suggested procedure (Lychagina, T.A. and Nikolayev, D.I. (2003). Phys. Stat. Sol. (a), 195(N2), 322–334.) for the case of hexagonal symmetry to evaluate the influence of the grain number in the sample on the calculated elastic properties. This procedure was carried out for graphite that is one of the widespread, applicable and highly anisotropic materials.

High-Resolution Imaging of Texture and Microstructure by the Moving Detector Method

In order to describe texture and microstructure of a polycrystalline material completely, crystal orientation g={ϕ1Φϕ2} 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.

Use of Synchrotron Diffraction Data for Describing Crystal Structure and Crystallographic Phase Analysis of R-Phase NiTi Shape Memory Alloy

Sitepu et al. (Sitepu, H., Schmahl, W.W., Khalil Allafi, J., Eggeler, G., Dlouhy, A., Reinecke, T., Brokmeier, H.G., Tovar M. and Többens, D.M. (2002b). Texture and quantitative phase analysis of aged Ni-rich NiTi using X-ray and neutron diffractions. Materials Science Forum, 394-395, 237-240.) showed that Rietveld refinement with generalized spherical harmonic (GSH) description for neutron powder diffraction (ND) data of the aged (673 K, 20 h) Ni-rich NiTi shape memory alloy (Sitepu H. (2002). Assessment of preferred orientation with neutron powder diffraction data. J. Appl. Cryst, 35, 274–277); of nominal composition 50.7 at.% Ni at 294K consists of four phases: precipitate (Ni4Ti3), R-phase, monoclinic (B19′) and some residual cubic (B2). Therefore, they concluded that the differential scanning calorimetry (DSC) first peak, on cooling, (321 K) is not due to the formation of the R-phase alone. The second, lower DSC peak (271 K) is due to the transformation of R-phase and residual B2 phase to B19′ phase. The structural refinement of R-phase problem, which was neglected in the previous study, was undertaken with great care in this study. The objective of the present article is to use the third generation synchrotron X-ray source at the European Synchrotron Research Facility (ESRF) in Grenoble, which make available X-ray beams of higher energy and much higher intensity than laboratory X-ray sources, for describing crystal structure of the R-phase in 50.75 at.% Ti–47.75 at.% Ni–1.50 at.% Fe ternary alloy. The synchrotron diffraction data of R-phase were analyzed using the Rietveld refinement with GSH description. The results showed that no significant improvement in fit is found when the inversion center is removed from the P3¯ model, suggesting that the space group is indeed P3¯ and not P3.

Intensity Correction in Texture Measurement of Polycrystalline Thin Films by X-Ray Diffraction

The tilting of a specimen may not only result in defocusing effect, but also in a change of irradiated volume during texture measurement for thin films and coatings by using X-ray diffraction. The influence on diffraction intensity has to be considered in order to obtain an accurate result of texture analysis. The effect of irradiated volume can be formulated as a function of the thickness and the linear absorption of a studied film material, the tilt angle of the specimen and the Bragg angle of diffraction, and then eliminated. In view of that the preparation of a randomly oriented specimen would be difficult, a simple and convenient method is hereby proposed to correct the defocusing effect from known data of existing bulk powder specimens with random orientation by interpolation (or extrapolation). The two correction methods were experimentally verified to be effective and reliable.