On ab initio indexing of Laue diffraction patterns

The Laue method allows for fast pattern acquisition, but its use in structural studies is limited by the complexity of data processing. In particular, automatic ab initio indexing of Laue patterns is not trivial. This paper describes measures improving the effectiveness of indexing software. The first such measure is to adjust the positions of Laue spots on the basis of a mesh of lines fitted in a consistent way. Two other modifications enlarge the set of cells tested as potential primitive lattice cells. The last modification concerns eliminating solutions representing superlattices of the true reciprocal lattice. The impact of using these schemes on the chances of obtaining correct indexing solutions is illustrated. The described procedures can be implemented to create fully automatic software for ab initio indexing of Laue patterns.

SPECIFICITY OF APPLICATION OF X-RAY METHODS OF «SWING» AND LAUE IN DETERMINING THE QUALITY OF THE STRUCTURE OF CASTINGS OF NICKEL HEAT-RESISTANT ALLOYS

Systematically analyzes and justifies the characteristics of equipment operating in monochromatic radiation by the «swing» method and in polychromatic radiation by the Laue method in relation to the specifics of controlled samples in the technology of single-crystal casting from nickel heat-resistant alloys. The main application of the «swing» method is the mass control of seed blanks, seedings, growth cones of samples and blades. The main application of the Laue method is local measurements of block misorientation in the casting of the turbine blade, determination of the crystallographic orientation misorientation in controlled areas on the blade. An optimized configuration is proposed for a compact modification of a diffractometer operating in monochromatic radiation for mass control of the structure in production.

APPLICATION OF THE LAUE METHOD TO STUDY THE STRUCTURE OF A NICKEL HEAT-RESISTANT ALLOY SAMPLE DESTROYED DURING MECHANICAL PROCESSING

A study of the structure of a single-crystal sample of a nickel heat-resistant alloy, brittle destroyed by mechanical cutting. The study was carried out using x-ray diffractometry – «swing» and the Laue method. The possibilities of the Laue method for studying local defects of various origin are shown. Based on the obtained data, an assumption is made about the recrystallization nature of structural defects in a single crystal of a nickel heat-resistant alloy; the elastic properties of the single crystal are estimated.

Correct interpretation of diffraction properties of quartz crystals for X-ray optics applications

Quartz has hundreds of strong Bragg reflections that may offer a great number of choices for making fixed-angle X-ray analyzers and polarizers at virtually any hard X-ray energies with selectable resolution. However, quartz crystals, unlike silicon and germanium, are chiral and may thus appear in two different forms of handedness that are mirror images. Furthermore, because of the threefold rotational symmetry along thecaxis, the {h1h2h3L} and {h2h1h3L} Bragg reflections may have quite different Darwin bandwidth, reflectivity and angular acceptance, although they have the same Bragg angle. The design of X-ray optics from quartz crystals therefore requires unambiguous determination of the orientation, handedness and polarity of the crystals. The Laue method and single-axis diffraction technique can provide such information, but the variety of conventions used in the literature to describe quartz structures has caused widespread confusion. The current studies give detailed guidelines for design and fabrication of quartz X-ray optics, with special emphasis on the correct interpretation of Laue patterns in terms of the crystallography and diffraction properties of quartz. Meanwhile, the quartz crystals examined were confirmed by X-ray topography to have acceptably low densities of dislocations and other defects, which is the foundation for developing high-resolution quartz-based X-ray optics.

In-house energy resolved Laue XRD measurements with a Pilatus detector

The use of 2D position and energy sensitive hybrid pixel Pilatus detectors allows performing energy-dispersive analysis of Bragg reflections [1]. This significantly improves the classical Laue experiments enabling the unique determination of the crystal lattice and resolving the higher order harmonics. It allows quantitative crystal structure determination using the Laue method without having any priory information about the crystal [2]. Such energy-dispersive Laue diffraction (EDLD) experiments can be performed with a white X-ray beam either from a synchrotron source or from conventional X-ray tubes. The second approach looks less profitable due to its lower irradiation intensity, but this can be compensated considering the better control of white beam spectra by applying different voltage/current settings during the tube operation. Thus, one can efficiently combine the primary beam and XRD measurements using the same Pilatus detector. This allows the implementation of the energy resolved (color Laue) method for any conventional XRD diffractometer equipped with a Pilatus detection system. In the present work EDLD experiments with a conventional X-ray tube were combined with corresponding primary beam measurements using a 300K Pilatus detector tuned for operation within an energy range of 4-25 keV at energy resolution <0.12 keV. Such a combination simplifies several data correction procedures (the spectral intensity distribution, the sample absorption etc.) significantly. Following our developed intensity correction protocols the structure refinement of a reference quartz sample could be achieved with R-factor <0.10. Possible applications of this method (e.g. quantitative XRD studies with stationary crystals) and the details for its further development will be discussed.

Two Methods of Studying Structure Perfection of Single Crystal Nickel-Based Superalloys

The article presents the comparison of two methods: classical X-ray topography and the modern automatic X-ray OD-EFG diffractometer. Both methods were applied to study the crystal orientation of turbine blades of single crystal nickel-based superalloys. The solidification of a hollow assembly structure for 5 various blades was carried out by the Bridgman method at the Research and Development Laboratory for Aerospace Materials at Rzeszow University of Technology using an ALD Vacuum Technologies vacuum furnace. Ceramic moulds made of Al2O3 were used. The alloy temperature during casting into the mould amounted to 1550°C. The specimens for Laue method tests were cut out from the blades at withdrawal rates of 1, 2, 3, 4, and 5 mm/min.