Papers by Keyword: X-Ray Imaging

Abstract: To detect and characterize materials defects in fiber composites as well as for evaluatingthe three-dimensional local fiber orientation in the latter, X-ray micro-CT is the preferred methodof choice. When micro computed tomography is applied to inspect large components, the method isreferred to as region-of-interest computed tomography. Parts can be as large as 10 cm wide and 1 mlong, while the measurement volume of micro computed tomography is a cylinder of only 4 − 5 mmdiameter (typical wall thickness of fiber composite parts). In this report, the potentials and limits ofregion-of-interest computed tomography are discussed with regard to spatial resolution and precisionwhen evaluating defects and local fiber orientation in squeeze cast components. The micro computedtomography scanner metRIC at Fraunhofer‘s Development Center X-ray Technology EZRT deliversregion-of-interest computed tomography up to a spatial resolution of 2 μm/voxel, which is sufficientfor determining the orientation of natural or synthetic fibers, wood, carbon and glass. The mean localfiber orientation is estimated on an isotropic structuring element of approximately 0.1 mm length bymeans of volume image analysis (MAVI software package by Fraunhofer ITWM). Knowing the exactlocal fiber orientation is critical for estimating anisotropic thermal conductivity and materials strength.

Abstract: AlN single crystals were prevented from cracking by simultaneous growth and evaporation of SiC substrates. The freestanding crystals (<1 mm thick) were proved continuous by synchrotron phase contrast imaging and used as a model system to investigate the type of dislocation structure near AlN/SiC interface by x-ray diffraction techniques. We have found that, unlike the situation in GaN films, where predominantly edge-type threading dislocations cross the layer along its normal, the dislocations configure to form mosaic structure. We suggest a theoretical model that describes the misfit stress relaxation in growing AlN crystal.

Abstract: Transforming industrial wastes into construction materials through recycling is a feasible alternative that contributes to reduce the consumption of natural resources. Besides, modern civil construction seeks strong lightweight building materials. Due to their low density, wind turbine blade manufacturing waste and EPS post-consumer packaging can be used for this purpose. Such work uses X-ray imaging to evaluate the spatial distribution of these wastes in Portland cement concrete. Test specimens were produced containing wind turbine blade waste replacing part of the gravel content, and EPS waste replacing part of the sand content. X-ray images of the test specimens reveal that the waste is distributed homogeneously in the matrix. Furthermore, the mechanical strength of these test specimens meets the requirements of the Brazilian technical standards for non-load bearing concrete blocks.

Abstract: We report on the growth method and the structural characterization of freestanding AlN crystals. An AlN layer is grown on a gradually decomposing SiC substrate yielding a freestanding crack free 2H single crystal with dislocation density 5×10⁴ cm^–2 and without grain boundaries as confirmed by synchrotron radiation phase contrast imaging and topography data. Wafers of 600–1000 μm thick and up to 15 mm in diameter are obtained. The thermal stress distribution in a conventional AlN/SiC structure is discussed. Theoretical estimates show that cracking of AlN layers is a natural result of their growth on undecomposed SiC substrates.

Abstract: In the work digital x-ray apparatus on the basis of the gas-discharge linear detector is considered. X-ray images of laboratory rats are presented. Application prospects of gas-discharge detectors as a solution of the up-to-date radiographic problems are deduced.

Abstract: Position resolved structural information from polycrystalline materials is usually obtained via micro beam techniques illuminating only a single spot of the specimen. Multiplexing in reciprocal space is achieved either by the use of an area detector or an energy dispersive device. Alternatively spatial information may be obtained simultaneously from a large part of the sample by using an array of parallel collimators between the sample and a position sensitive detector which suppresses crossfire of radiation scattered at different positions in the sample. With the introduction of an X-ray camera based on an energy resolving area detector (pnCCD) we could combine this with multiplexing in reciprocal space.

Abstract: In the present work, solidification of hypoeutectic, eutectic and hypereutectic Al-Cu alloys was illustrated by synchrotron X ray imaging, and the CET of hypoeutectic alloy was picked out to thorough investigated. The mechanism of hypoeutectic dendrites fragment behaviors among the nucleation area was studied by in-situ imaging and first-principles computation. The results show that the density difference between the fragments and the enriched melt leads to the movement of the fragments. The ejected fragments contributed to the columnar-eutectic transition and expanded the breadth of mush zone in front of the solid/liquid interface.

Abstract: Diamond composite materials are classified as superhard and exhibit exceptional abrasive resistance. Cemented tungsten carbide tools with a thick coating of diamond composite material (PCD) are finding increased usage in materials cutting operations in manufacturing, mining, minerals, gas and petroleum exploration and civil construction industries. Two major advantages derived from these coated tools are: (a) increased wear resistance and hence increased life-span of these tools and (b) their proven ability to handle “difficult-to-machine” materials as well as high-strength, extremely abrasive materials such as quartz-rich rocks, granites and basalts. In this research, the variability of the wear resistance of PCD coated tungsten carbide is correlated with microstructural variations. A detailed study of the microstructure and distribution of phases was performed using SEM, cathodoluminescence (CL) imaging, direct x-ray imaging, Raman spectroscopy as well as residual stress measurements using neutron diffraction.

Abstract: The columnar to equiaxed transition (CET) has been widely studied for many years [1] because this phenomenon is observed in metallurgical applications like castings. In non refined alloys, detachment of dendrite fragments is the most probable mechanism responsible for the formation of an equiaxed microstructure [1]. In this frame, melt convection influences the grain structure evolution by playing a role in the fragmentation phenomena [2].

Abstract: At the HARWI II beamline at the GKSS outstation at DESY a new experiment for position sensitive diffractometry and tomography called DITO was built and commissioned this year. Due to the available high energy synchrotron radiation with photon energies up to 100 keV it is possible to investigate the bulk of metallic samples of a few mm thickness with both methods. The diffractometry detector allows the investigation of the phase composition as well as phase sensitive determination of residual stresses with a spatial resolution of 6 μm while the tomography detector can either measure a whole tomogram in high resolution mode with a spatial resolution of 2 μm within 3 to 4 hours or in high speed mode recording a whole tomogram within 15 seconds with a spatial resolution of 40 μm.