Volume 111, Issue 1

The addition of Zn to the Mg–Nd system improves the yield strength and creep resistance, however its influence on the intermetallic phases in the ternary system is not yet fully understood. Understanding the sequence of phase-formation and phase-evolution during solidification and processing is essential to microstructure design. The solidification was investigated with in-situ synchrotron radiation-diffraction and tomography during cooling from the molten state to 200°C to investigate the phase-formation and transformation characteristics. The solidification starts with α-Mg followed by two distinct intermetallic phases T2 and T3. The results suggest that Zn stabilizes the Mg 3 Nd phase and accelerates precipitate formation. The dendritic morphology changes during solidification towards coarser shapes, thus impedes feeding and promotes hot tearing.

The local dynamics of dendritic side arms during the growth stage were studied by in-situ radiography observations at high spatial resolution of better than 1 μm. A flat sample of a Ga–In alloy was solidified top-down applying a vertical temperature gradient. The evolving dendritic microstructure was visualized using synchrotron X-ray imaging at the beamline ID19 (ESRF, France). The experimental investigations on the dendrite evolution revealed a transition from a four-fold symmetry to a hyperbranched dendritic morphology. Both the side arm-splitting phenomenon – responsible for this morphological transition – as well as the arm growth dynamics were characterized using image processing.

In this work, we investigated the re-solidification dynamics and microstructure of aluminium AA5005 welded by fibre laser. The re-solidification process was visualized by high-speed X-ray imaging at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). The final microstructure was studied by electron backscatter diffraction. The experiments were performed in both conduction and keyhole weld regimes. The results show that fine and equiaxed structure is obtained for conduction welding due to very high cooling rate. Keyhole welding also shows similar structure at the beginning of re-solidification, followed by a columnar microstructure.

Synchrotron tomography was carried out during in-situ tensile tests of fiber metal laminates formed by 3 layers of friction stir welded AlMg4.5Sc0.2 (AA5024) alloy foils and 2 layers of glass fiber reinforced polymer. The aim of these investigations was to identify the damage mechanisms and their sequence during quasi-static loading conditions of the fiber metal laminate as well as to determine microstructural features responsible for tensile damage. The microstructural and geometric changes produced by the friction stir welding process on the aluminum foils resulted in a strain localization and further damage accumulation in the welded aluminum foils, where the smallest transverse areas and lowest tensile properties were found.

One fundamental topic in metallography is determining relations between microscopic arrangements of phases and defects, and macroscopic properties (such as tensile strength, effective stiffness tensor, effective conductivity, permeability) which are important for materials application. For multiphase materials such as aluminum–silicon alloys our work demonstrates how – in particular – three-dimensional geometric microstructure characteristics, such as particle sphericity, connectivity and contiguity can be measured accurately from 3D X-ray computed tomography scans. This study details a simple yet very effective imaging toolchain for measuring these quantities. By tailoring the three-dimensional morphology of the alloys’ phases through composition, cooling and thermo-mechanical treatment one can establish a multidimensional materials database. For a given function and application, such a database would allow for optimized selection of alloy and processing, e.g. using a material which is specifically designed and produced according to its properties. The extraction of meaningful stochastic parameters from 3D CT scans of metallic alloys is therefore highly important.

The fuel rod claddings in nuclear light water reactors are made of zirconium alloys. Corrosion of these alloys during operation and in particular high temperature oxidation during nuclear accidents results in the production of free hydrogen. The cladding can absorb this hydrogen. It affects the mechanical properties of the cladding material. Hydrogen embrittlement of these materials provides the risk of brittle fracture of the cladding by thermo-shock during emergency cooling. At KIT the behaviour of cladding materials under different hypothetical nuclear accident scenarios was investigated. One focus was on hydrogen absorption and distribution/re-distribution in the alloys. The hydrogen distribution was determined mainly by neutron tomography. Examples for the determination of the 3D hydrogen distribution in cladding tubes after loss of coolant accident simulation tests are given and discussed.

The quality of metal objects fabricated via laser powder bed fusion are highly affected by process parameters, and their influence on final products is yet to be fully explored. In this work, pyrometry signals of the melt pool were collected from a set of stainless-steel samples during manufacturing and the effect of laser power on porosity and roughness of final printed parts was analyzed. Results show that the melt pool pyrometry signal of contours increases with higher laser power, whereas it is lower and decreases for the infilled part. Post-built X-ray computed tomography imaging reveals that porosity decreases while sample roughness increases upon increasing laser power. The decrease in porosity with increasing laser power is attributed to the larger size of the contour welds that were printed first, leading to an increase in dimension of the final products.

Mechanochemically synthesized metal–organic framework material HKUST-1 in combination with acrylonitrile butadiene styrene polymer was used to form a polymer metal–organic framework composite material by a simple extruder. This composite filament was used for 3D printing. X-ray diffraction measurements were used to prove the homogeneous distribution of the metal–organic framework in the polymer on a centimeter scale, whereas X-ray Absorption Edge Tomography using a synchrotron radiation source was able to evaluate the 3D distribution of the metal–organic framework material both in the filament and the resultant printed sample with a resolution of a few μm. Our very first data indicate that, apart from a few clusters having significantly higher Cu concentration, HKUST-1 is distributed homogeneously down to the 100 μm length scale in both polymer bulk materials in the form of clusters with a size of a few μm. Absorption Edge Tomography in combination with data fusion also allows for the calculation of the metal–organic framework amount located on the external polymer surface.

In granular media, topological features are known to determine the effective material properties and boundary behavior when interacting with other structural components. X-ray computed tomography results are reported on sphere packing structures in slender prismatic containers ( X = 20, Y = Z = 80 mm), filled and vibrated with both monosized spheres (diameter d = 2.4 mm), Exp. (M), and polydisperse spheres (1 mm < d < 1.25 mm), Exp. (P). Packing structures were characterized by void fraction distributions, coordination numbers, contact angle distributions and Voronoi packing fractions. In (M), an almost perfect hexagonal dense packing exists in the total volume, associated with a packing fraction γ t ≈0.68. In additional packing experiments, large γ t values were achieved as well. Although the d spread in (P) is relatively small, significantly different results are obtained: γ t ≈0.62, regular structures are restricted to narrow wall zones and distributions in the container volume are nonhomogeneous. It is argued that the small degree of ordered structure is a characteristic feature of polydispersity for efficiently vibrated sphere packings.

Bones are nanocomposites of protein, mineral and water that form mineralized collagen fibrils arranged in a variety of layered lamellae. Bone material has a long evolutionary record and specific bones attain shapes and microstructures that have well stood the test of time such that they can be considered optimized to match their function. Further, most bones typically contain entombed living cells, osteocytes responsible for adaptation, healing and biochemical signaling. The bones of pike fish ( Esox lucius ) are different because, as with other advanced teleost species, they evolved to eliminate osteocytes from the microstructure. This suggests that these cells are not needed because these bones are more damage resistant than mammalian bones. Here we explore details of this biologically-grown structure, using a combination of light and X-ray based characterization methods. We report the three-dimensional arrangement and composition of the heavily cyclically-loaded pivot of the cleithrum bone in the pectoral girdle of pike. By combining absorption and phase contrast-enhanced micro-computed tomography, electron microscopy, polarized light microscopy and second harmonic generation multi-photon confocal laser scanning microscopy we reveal the principle layout of the bone of this predator which we determine at the millimeter, micrometer and nanometer lengthscales.

Time-resolved microtomography with high frame rate, high lateral resolution and sufficiently high contrast allows for observing three-dimensional motion of particles in two-phase solid–liquid flows through porous structures. Knowledge of the interaction between the particles and an activated surface of the pore space is important for simulation of the flow as a part of the design of porous structures with improved properties. Investigations on such structures are, for example, a prerequisite for the development of new technologies for industrial cell chromatography. From the 3D image sequences obtained by time-resolved microtomography it is possible to estimate various flow characteristics such as the particle deposition rate at the surface of the pore space and the fraction of particles moving close to the surface.