Datei im Netzwerk der BAM verfügbar ("Closed Access")
Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (73)
- Beitrag zu einem Tagungsband (11)
- Vortrag (11)
- Beitrag zu einem Sammelband (2)
- Posterpräsentation (2)
Schlagworte
- Electron backscatter diffraction (31)
- EBSD (29)
- Simulation (10)
- SEM (7)
- Orientation relationship (6)
- Pattern matching (6)
- Phase identification (6)
- XRD (6)
- Crystal orientation (5)
- Microstructure (5)
Organisationseinheit der BAM
- 5 Werkstofftechnik (27)
- 5.1 Mikrostruktur Design und Degradation (25)
- 5.2 Metallische Hochtemperaturwerkstoffe (3)
- 5.5 Materialmodellierung (3)
- 9 Komponentensicherheit (2)
- 1 Analytische Chemie; Referenzmaterialien (1)
- 1.4 Prozessanalytik (1)
- 6 Materialchemie (1)
- 6.1 Oberflächen- und Dünnschichtanalyse (1)
- 9.0 Abteilungsleitung und andere (1)
Eingeladener Vortrag
- nein (11)
The orientation relationship (OR) between the bcc and fcc phase in the plessite microstructure of the iron meteorites Watson, Agpalilik and Gibeon has been analysed in a scanning electron microscope using electron back-scattered diffraction (EBSD). A very strong OR exists, independently on the analysed plessite type and the observed spreading of single orientation data. The agreement between the experimental orientation distribution and existing models varies for each meteorite. The black plessite in the Agpalilik corresponds to the Nishiyama-Wassermann model whereas the Duplex plessite of the Gibeon meteorite shows an OR close to the Kurdjumov-Sachs model. The Watson meteorite is strongly deformed so that a general OR is difficult to determine due to the blurred experimental orientation distribution.
An experimental Co-base superalloy was designed from the Ni-base system by exchange of Ni and Co concentrations. The alloy consist of a Co-matrix (γ phase) strengthened by cuboidal precipitates Co3(Al,X) (γ' phase). The γ'-solvus temperature is 1?005?°C. [001] single crystals of this alloy were solidified and tested for tension at different temperatures up to 1?000?°C. It was found that the Co-base alloy has a much lower yield stress than a corresponding Ni-base alloy, but a much higher ductility. The partitioning behaviour of the alloying elements in the Co-base alloy and the deformation mechanisms were investigated by scanning and transmission electron microscopy.
Since the BSE signal depends on many factors, like the chemistry of the phase and the acceleration voltage, the size and position of the detector array is (slightly) different from phase to phase so that an (iterative) post-processing of the stored patterns is highly recommended. The derived BSE signal can be used for phase assignment in high resolution and high speed maps when EBSD fails and/or EDS (energy dispersive spectroscopy) needs too much time for a suitable and parallel signal acquisition.
Pole figures are often used to present crystal orientation data. The huge number of single orientation measurements acquired by electron backscatter diffraction (EBSD) poses a challenge for pole figure representation due to the large number of calculations required. This significantly reduces the speed at which the data may be rotated and affects the ability to switch between different projection types. In the present work, it will be shown that satisfactory representation of orientation data in different projection types can generally be achieved by an imaging of a spherical projection. With this approach, explicit calculation of the projections is no longer required, allowing for both real-time dataset rotation and real-time switching between all projection types relevant to materials science. The technique can be applied to any other directional property distribution, for example, not only for EBSD orientation presentation.
(Bio)geochemical cycling of gold (Au) has been demonstrated in present-day (semi)-arid, (sub)-tropical and temperate environment. Hereby biofilms on Au-bearing mineral- and Au-particle surfaces drive Au dispersion and reconcentration, thereby (trans)forming the particles. However, it is unknown if biogeochemical cycling of Au occurs in polar environments, where air temperatures can reach −40 °C and soils remain frozen for much of the year. Therefore, placer Au-particles, soils and waters were collected at two placer mining districts in arctic Finland, i.e., the Ivalojoki and Lemmenjoki goldfields. Sites were chosen based on contrasting settings ((glacio)-fluvial vs. glacial-till deposits) and depths (surface to 5m below current surface). Gold particles were studied using a combination of tagged 16S rRNA gene next generation sequencing and electron microscopic/microanalytical techniques. Across all sites a range of Au-particle morphologies were observed, including morphotypes indicative of Au dissolution and aggregation. Elevated Au concentrations indicative of Au mobility were detected in placer particle bearing soils at both districts. Typically Au-particles were coated by polymorphic biofilm layers composed of living and dead cells embedded in extracellular polymeric substances. Intermixed were biominerals, clays and iron-sulfides/oxides and abundant secondary Au morphotypes, i.e., nano-particles, microcrystals, sheet-like Au, branched Au networks and overgrowths and secondary rims. Biofilms communities were composed of Acidobacteria (18.3%), Bacteroidetes (15.1%) and Proteobacteria (47.1%), with β-Proteobacteria (19.5%) being the most abundant proteobacterial group. Functionally, biofilms were composed of taxa contributing to biofilm establishment, exopolymer production and nutrient cycling, abundant taxa capable of Au mobilization, detoxification and biomineralization, among them Cupriavidus metallidurans, Acinetobacter spp. and Pseudomonas spp., were detected. In conclusion, these results demonstrate that placer Au-particle transformation and Au dispersion occur in cold, arctic environments. This corroborates the existence of biogeochemical Au cycling in present-day cold environments.
The Bravais lattices and their lattice parameters are blindly determined using electron backscatter diffraction (EBSD) patterns of materials with cubic or tetragonal crystal structures. Since the geometric relationships in a single EBSD pattern are overdetermined, the relative errors of determining the lattice parameters as well as the axial ratios are confined to about 0.7 ± 0.4% and 0.07 ± 0.03%, respectively, for ideal simulated EBSD patterns. The accuracy of the crystal orientation determination reaches about 0.06 ± 0.03°. With careful manual band detection, the accuracy of determining lattice parameters from experimental patterns can be as good as from simulated patterns, although the results from simulated patterns are often better than expermental patterns, which are lower quality and contain uncertain systematic errors. The reasonably high accuracy is obtained primarily because the detection of the diffracting-plane traces and zone axes is relatively accurate. The results here demonstrate that the developed procedure based on the EBSD technique presents a reliable tool for crystallographic characterization of the Bravais lattices of unknown phases.
Among the borates in the Middle European Zechstein Salt Succession boracite Mg3[B7O13Cl] is the most common mineral in quantity and local distribution. An exceptional enrichment is observed in Stassfurt Serie Z2) in the Stassfurth seam K2H. Boracite is to be found in two varieties: individual crystals in cubic, tetrahedral or dodecahedral habit on the one hand and fibrous crystals so-called “stassfurtite” on the other hand. The formation conditions such widely spread borates in the salt succession are ambiguous in two respects. First of all the synthetic formation of boracites is to be made by hydrothermal or melt conditions. Both processes can be suspended for the salt succession. Furthermore the cubic modification is stable above 265°C for the Mg-boracite. The cubic, tetrahedral or dodecahedral habit could be used as a geothermometer, but such conditions can be exclude by the paragenetic minerals, esp. carnallite (MgKCl3 x 6H2O). The chemical composition of orthorhombic, pseudo-cubic boracite depends on the location. Pure Mg-boracite in hexahedral habit and in fibrous habit, so-called “stassfurtite”, occurs in the North Harz region, whereas the Fe-, Mn-, Mg-boracite appears in the South Harz region. Until now the source of boron, the time of formation of crystals, but also the reasons for the differences in habit of the single hexahedral crystals are still unclear. The formation during a diagenetic/metamorphic process is evident. However, the preferred formation in Stassfurt seam could be an indication for the boron enrichment in an early diagenetic process. Furthermore permit the determination of the thermal stability and the volatile content of crystals conclusions to the chemical composition of the fluid. The observed variation suggests that the condition of crystal growth as well as the chemical composition of fluid repeatedly changed over the time. Randomly occuring xenomorpheous anhydrite and magnesite inclusions within single boracite crystals have been interpreted as an indication to factors of chemical milieu during the formation of crystals. The reversible phase transition temperature of the boracite is a linearly function of the iron and manganese content and varies from 265°C for Mg-boracite to 330°C for Fe(Mn)-boracite. The thermal decomposition of boracite is determined by two processes. The decomposition started with a boron-chlorine release (BOCl?), having a maximum rate at 1050°C. Additionally to this release one observes a simultaneous emission of H2O, HCl, HF, CO2 , N2 , SO2 , H2 , and hydro carbons. The results give evidence for the aged approach of a secondary formation of boracite within the complete Stassfurt seam, possibly in connection with the formation of salt diapirs in the Jura and Cretaceous period. The wider environmental distribution of borates is an indication of chemical transport processes within the salt succession. This should be a more important issue in the discussion about the utilisation of salt diapirs for the storage of nuclear waste.
CALM is software for determining the Bravais lattice type and the resulting lattice parameters from a single Kikuchi pattern. It requires the definition of 4 bands and a single bandwidth from which all other band positions as well as bandwidths are derived. For band detection, it uses the Funk transform, which allows detection of twice as many bands as usual. CALM works for any symmetry and requires low-noise patterns of at least 320x240 pixels. The resulting errors are <2% even for such small patterns, assuming good quality. The relative errors are <0.5%. However, this requires a projection centre position best derived from a sample of a cubic phase in CALM. However, this must have been recorded under identical conditions. Hundreds of Kikuchi patterns of phases with different symmetries were examined.
Using channeling-enhanced energy-dispersive X-ray spectroscopy (EDX), we demonstrate polarity sensitive orientation determination of a non-centrosymmetric crystal in the scanning electron microscope. The authors observe a characteristic asymmetry in the channeling-enhanced, angle-dependent EDX data of a GaAs sample, which is in good agreement to simulations using the dynamical theory of diffraction for the incident electron beam. This allows us to assign the orientation of the GaAs crystal according to the non-centrosymmetric point group. The method shown here overcomes the limitation of a reduced point-group sensitivity of electron backscatter diffraction Patterns and electron channeling patterns for crystalline phases that contain atoms of approximately equal electron scattering cross sections.
Characterization of the fcc/bcc orientation relationship by EBSD using pole figures and variants
(2004)
The orientation relationship (OR) between fcc and bcc lattices are described by crystallographic fundamentals using the example of Kurdjumov-Sachs (K-S) and Nishiyama-Wassermann (N-W). Complete pole figures containing all variants will be used to distinguish even between slightly different ORs. EBSD on iron meteorites and duplex steel has been used to analyse a large number of crystal orientations with regard to a high statistical significance and a high probability to capture all variants in a single measurement. It is shown that the use of fixed OR models like K-S, N-W, Bain, Pitsch, or Greninger-Troiano does not satisfacturally reflect the observed experimental pole distributions. It is not convenient to use high-indexed lattice planes and directions to describe the small deviations from the given models. The Euler subspace representation offers a readily comprehensible tool to get an idea about the characteristic of the experimentally detected OR.