Hans-Jürgen Ullrich

X‐ray Rotation‐Tilt‐Method — First Results of a new X‐ray Diffraction Technique

The XRT technique is a further special X-ray microdiffraction method where local X-ray interferences are produced by directing an X-ray or synchrotron beam from an external source with default monochromatic radiation of high intensity and a small diameter (e.g. application of capillary optics) on a crystalline region of a sample. Thereby for each diffracting net plane set a cone can be indicated with the half-opening angle equal to (90°Θhkl) for which the Bragg equation (1) is satisfied.

A Three-Dimensional Skeletal Reconstruction of the Stem Amniote Orobates pabsti (Diadectidae): Analyses of Body Mass, Centre of Mass Position, and Joint Mobility

Orobates pabsti, a basal diadectid from the lower Permian, is a key fossil for the understanding of early amniote evolution. Quantitative analysis of anatomical information suffers from fragmentation of fossil bones, plastic deformation due to diagenetic processes and fragile preservation within surrounding rock matrix, preventing further biomechanical investigation. Here we describe the steps taken to digitally reconstruct MNG 10181, the holotype specimen of Orobates pabsti, and subsequently use the digital reconstruction to assess body mass, position of the centre of mass in individual segments as well as the whole animal, and study joint mobility in the shoulder and hip joints. The shape of most fossil bone fragments could be recovered from micro-focus computed tomography scans. This also revealed structures that were hitherto hidden within the rock matrix. However, parts of the axial skeleton had to be modelled using relevant isolated bones from the same locality as templates. Based on the digital fossil, mass of MNG 10181 was estimated using a model of body shape that was varied within a plausible range to account for uncertainties of the dimension. In the mean estimate model the specimen had an estimated mass of circa 4 kg. Varying of the mass distribution amongst body segments further revealed that Orobates carried most of its weight on the hind limbs. Mostly unrestricted joint morphology further suggested that MNG 10181 was able to effectively generate propulsion with the pelvic limbs. The digital reconstruction is made available for future biomechanical studies.

Precise determination of the lattice constant of LiF by means of X-ray divergent beam (pseudo Kossel-) technique via computer graphics and multiple intersections

The X-ray interference patterns obtained by the divergent beam transmission technique (pseudo Kossel technique in transmission mode) permit an evaluation of high precision. Especially the low resolution triple intersections appearing in the pattern can be utilized for precise determination of lattice constants. For cubic crystals the parameters can be calculated directly using analytical methods. The computer graphics method is also applicable for crystal systems with low symmetry. It is shown on patterns from LiF obtained with Fe-K and Cu-K radiation that the computer graphics method provides a fast way for the precise determination of lattice constants.

Investigations in the ternary system Ti-Mo-N by means of EPMA and XRD

Arc-melted ternary Ti-Mo-N alloys were heat treated at 1423 K in order to evaluate the compositions of the equilibrium phases. The composition of the bcc phaseβ-TixMo1−x with respect to Mo and Ti was determined by electron probe microanalysis (EPMA) and lattice parameter measurements (XRD). In order to avoid the effects of plastic deformation caused by powdering the ductileβ-TixMo1−x alloys, the lattice parameter measurements were carried out on small particles of the compact samples using Debye-Scherrer cameras. The EPMA and XRD results agree within the expected range of accuracy. Apparently the solubility of nitrogen inβ-TixMo1−x is low and does not perceptibly affect EPMA and XRD results. The relationship between the lattice parameter and the nitrogen content ofδ-TiN1−x was applied to determine the composition ofδ-TiN1−x in equilibrium withβ-TixMo1-x No solid solubility of Mo in TiN1−x could be detected. The tie lines at 1423 K between the two phases were established.

Fortschritte auf dem Gebiet der Kossel-Technik

Die von W. Kossel entdeckten „Rontgeninterferenzen aus Gitterquellen“ werden seit Mitte der sechziger Jahre haufiger zur Untersuchung kristalliner Festkorper eingesetzt. Eingeleitet wurde dieser Trend durch die Entwicklung von Kossel-Kameras fur Elektronenmikroskope und Elektronenstrahl-Mikroanalysatoren. Mit letzteren stehen leistungsfahige Gerate zur Verfugung, um die Vorteile, welche die Kossel-Interferenzen im Vergleich zu anderen Beugungsverfahren besitzen, in vollem Umfang auszunutzen. In Tabelle 1 werden die Vor-und Nachteile der Kossel-Technik aufgefuhrt.

Analyses about the influence of the natural oxide layer of aluminium on the brazeability in a shielding gas furnace

Aluminium is a widely used material in industrial processes due to its good material properties, e.g. minor density in combination with a high strength, good corrosion resistance as well as good thermal and electrical conductivity. For its application, a material joining is often necessary. In contrast to other well-brazeable materials, e.g. copper, aluminium has a significant disadvantage: its natural oxide layer at the surface. Due to this layer, there is always an additional surface activation necessary for welding and brazing, e.g. the effect of an arc, flux or vacuum. These methods are efficient, if the natural oxide layer corresponds to the standard thickness and composition. However, the properties of the natural oxide layer can vary due to a raised humidity in the ambient atmosphere or increased temperatures. This paper describes the constitution of the natural oxide layer and gives an overview about methods for analysing these only nanometer-thick layers. Additionally, a method is introduced for aluminium brazing in a shielding gas furnace without using flux. The mechanisms for this surface activation method are characterised. This method is used afterwards to analyse the correlation between the aluminium surface composition and the brazeability.

Investigation of (Mo,W)C Mixed Carbides by Electron Probe Microanalysis and Kossel Technique

Tungsten as an element has such a unique combination of outstanding properties that it is very difficult to find a substitute with similar properties. In alloys the task is somewhat simpler: tungsten in high speed steels has been successfully replaced at least partially by molybdenum in the past decades. Attempts to replace tungsten by molybdenum in the hardmetal industry, which takes up more than 50% of the total tungsten production, have been discouraged for a long time by the belief that molybdenum in hardmetal is harmful because of its tendency to form brittle subcarbide (Mo2 C)-needles or brittle complex compounds. It was only recently that Rudy and coworkers1 showed that tungsten atoms in WC can be replaced by molybdenum atoms without changing the crystal structure. Apparently a partial substitution of W in WC by Mo results in only gradual and minor changes in physical and mechanical properties. Hardmetals sintered with these mixed (Mo, W)C-carbides show nearly the same properties as straight WC-based hardmetals. The microstructure of Mo-substituted (Mo, W)C-Co hardmetals is distinctly different from that of unalloyed conventional WC-Co hardmetals. In (Mo, W)C-Co hardmetals the carbide grains have a zoned structure, which is easily observable in the etched microsection shown in Fig. 1. In order to gather further information on the homogeneity of composition and crystal structure within one single carbide grain, a combination of electron microprobe analysis (EPMA) and microbeam diffraction technique had to be employed.

Phase identification in Ti/TiN diffusion couples with the Kossel technique

A Ti/TiN diffusion couple, which had been prepared by isothermal annealing of a Ti sheet in nitrogen atmosphere at 1091 °C and quenched in water, was investigated by Kossel microdiffraction. Kossel patterns were obtained from all phases present in the diffusion couple (α-Ti(N), η-Ti3N2−x, ζ-Ti4N3−x and δ-TiN1-x)It could be shown that the Kossel technique has a superior lateral resolution (10 μm) compared to commercially used X-ray microdiffraction methods, especially in the case of weak X-ray radiation.

Radiation analytical material characterization of diamond layers deposited onto tungsten carbide

The characterization of diamonds deposited onto WC single crystals by means of the CVD-method is reported. Investigations were performed by scanning electron microscopy, X-ray diffraction methods and the Kossel reflection technique. Single diamond crystals were deposited in the form of icosahedrons. An orientation correlation between substrate single crystal and diamond crystals could not be proved. In the paper presented, reasons will be given for this fact.

Spezielle röntgenographische Mikrobeugung: Teil 2: Die Röntgen-Drehschwenk-Technik

Kurzfassung Es gibt weltweite Anstrengungen, Mikrobereiche kompakter Proben mittels Röntgenmikrobeugungsverfahren („X-ray Microdiffraction“) zu untersuchen. Die synchrotron- bzw. elektronenstrahlangeregte KOSSEL-Technik (Teil 1) und die neu entwickelte Röntgen-Drehschwenk-Technik (Teil 2) werden als spezielle röntgenographische Verfahren vorgestellt und hinsichtlich ihrer Einsatzmöglichkeiten und Grenzen verglichen. Ausgehend vom Funktionsprinzip der neuen Röntgen-Drehschwenk-Technik werden ausgewählte Anwendungen im Mikrobereich beschrieben. Eine vergleichende Betrachtung zur KOSSEL-Technik ergänzt die Darstellung.