Search

Pattern matching approaches to electron backscatter diffraction (EBSD) in the scanning electron microscope (SEM) provide qualitatively new possibilities for the microstructural analysis of chiral non-centrosymmetric phases due to the influence of dynamical electron diffraction effects on the formation of EBSD Kikuchi patterns. In the present study, we analyze the microstructure of polycrystalline alpha-quartz in an agate mineral sample. We identify characteristic intra-grain inversion domains of different handedness which are well-known from classical polarized light microscopy. As a result, the handedness-resolved microstructure of quartz can be imaged with the spatial and orientation resolution provided by EBSD in the SEM.

Electron backscatter diffraction (EBSD) patterns can exhibit Kikuchi bands with inverted contrast due to anomalous absorption. This can be observed, for example, on samples with nanoscale topography, in case of a low tilt backscattering geometry, or for transmission Kikuchi diffraction (TKD) on thicker samples. Three examples are discussed where contrast-inverted physics-based simulated master patterns have been applied to find the correct crystal orientation. As the first EBSD example, self-assembled gold nanostructures made of Au fcc and Au hcp phases on single-crystal germanium were investigated. Gold covered about 12% of the mapped area, with only two-thirds being successfully interpreted using standard Hough-based indexing. The remaining third was solved by brute force indexing using a contrast-inverted master pattern. The second EBSD example deals with maps collected at a non-tilted surface instead of the commonly used 70 degree tilted one. As TKD example, a jet-polished foil made of duplex stainless steel 2205 was examined. The thin part close to the hole edge producing normal-contrast patterns were standard indexed. The areas of the foil that become thicker with increasing distance from the edge of the hole produce contrast-inverted patterns. They covered three times the evaluable area and were successfully processed using the contrast-inverted master pattern. In the last example, inverted patterns collected at a non-tiled sample were mathematically inverted to normal contrast, and Hough/Radon-based indexing was successfully applied.

Zinc alloys have emerged as promising candidates for biodegradable materials due to their remarkable biocompatibility and favorable mechanical characteristics. The incorporation of alloying elements plays an essential role in advancing the tensile strength of Zn alloys. Nevertheless, achieving uniform dispersion of these elements poses challenges due to chemical segregation during solidification. In this study, rapid solidification followed by high-pressure torsion was successfully employed to fabricate Zn-Li-Mn-Mg-Cu alloys characterized by ultrafine-grained microstructures with evenly distributed nanometric intermetallic phases. A comprehensive examination, including phase composition, microstructural evolution, tensile properties and deformation mechanisms, was conducted. The impact of varying annealing temperatures on microstructural stability was systematically examined. The combined implementation of rapid solidification and high-pressure torsion yielded alloys with an average grain size below 360 nm, thereby demonstrating exceptional mechanical properties including yield stress (YS), ultimate tensile strength (UTS), and elongation to failure (Ef) equal to at least 325+-6 MPa, 350+-8 MPa and 40+-11 %, respectively. Heat treatment notably augmented the mechanical properties, resulting in a YS = 440+-11 MPa and UTS = 491+-6 MPa, while preserving plasticity (Ef = 23+-4 %) in the Zn-0.33Li-0.27Mn-0.14Mg-0.1Cu alloy. Nanoindentation strain rate jump tests identified thermally activated mechanisms and grain boundary sliding as dominant deformation mechanisms.

Crystals of the chemical elements manganese, tellurium, and selenium can show the effects of handedness. In order to sense the possible effects of a changing sense of chirality on the properties of samples from these elements, the potential presence of two, enantiomorphic, physically different, variants of these elemental crystal structures needs to be resolved in crystallographic analyses. Due to fundamental limitations of kinematical X-ray scattering in crystals, however, the effects of chirality in single-element crystals are very difficult to sense using standard X-ray diffraction techniques. In the present paper, we show that dynamical Kikuchi diffraction in the scanning electron microscope is sensitive to the local sense of chirality in crystals of single chemical elements. We demonstrate chirality assignment in $\beta$-manganese, and we determine the sense of crystal chirality from Kikuchi diffraction patterns of the trigonal structures of tellurium and selenium., Comment: 14 pages, 6 figures, updated references, moved supplementary figures into main text

The locally varying tetragonality in martensite grains of a high-carbon steel (1.2 mass percent C) was resolved by electron backscatter diffraction (EBSD) with a spatial resolution in the order of 100nm. Compared to spatially integrating X-ray diffraction, which yielded an average tetragonality of c/a=1.05, the EBSD measurements in the scanning electron microscope allowed to image a local variation of the lattice parameter ratio c/a in the range of 1.02 $\leq$ c/a $\leq$ 1.07. The local variation of tetragonality is confirmed by two different EBSD data analysis approaches based on the fitting of simulated to experimental EBSD patterns. The resulting EBSD-based tetragonality maps are pointing to a complex interaction of carbon concentration and local lattice distortions during the formation process of martensitic structures., Comment: 16 pages, 9 figures

Orientation determination does not necessarily require complete knowledge of the local atomic arrangement in a material. We present a method for microstructural phase discrimination and orientation analysis of phases for which there is only limited information available. In this method, experimental Kikuchi diffraction patterns are utilized to generate self-consistent standards for use in the technique of Electron Backscatter Diffraction (EBSD). As an application example, we map the locally varying orientations in samples of icosahedral quasicrystals observed in a Ti40Zr40Ni20 alloy.

We describe a lattice-based crystallographic approximation for the analysis of distorted crystal structures via Electron Backscatter Diffraction (EBSD) in the scanning electron microscope. EBSD patterns are closely linked to local lattice parameter ratios via Kikuchi bands that indicate geometrical lattice plane projections. Based on the transformation properties of points and lines in the real projective plane, we can obtain continuous estimations of the local lattice distortion based on projectively transformed Kikuchi diffraction simulations for a reference structure. By quantitative image matching to a projective transformation model of the lattice distortion in the full solid angle of possible scattering directions, we enforce a crystallographically consistent approximation in the fitting procedure of distorted simulations to the experimentally observed diffraction patterns. As an application example, we map the locally varying tetragonality in martensite grains of steel.