Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (34)
- Beitrag zu einem Tagungsband (5)
- Vortrag (3)
- Forschungsdatensatz (1)
Schlagworte
- EBSD (43) (entfernen)
Organisationseinheit der BAM
Eingeladener Vortrag
- nein (3)
A survey is presented on some characteristic features of meteoritic (Fe,Ni)3P which is an abundant and important minor phase of most iron meteorites. This mineral (named schreibersite/rhabdite) plays a decisive role during the formation of the so-called Widmanstätten pattern. Different transmission as well as scanning electron microscopic techniques have been applied to get more precise information about the real structure of the phosphide crystals, their chemical composition and the metal distribution across the phoshide/ kamacite interface. X-ray crystal structure determinations have been performed for selected (Fe,Ni)3P - cystals from various iron meteorites (Toluca, North Chile, Watson, Orange River, Morasko, Agpalilik, Odessa, Canyon Diablo). These experiments revealed a metal ordering, i.e. for the three non-equivalent metal positions a different substitution of Fe by Ni has been found. The perfection of the brittle (Fe,Ni)3P samples differs appreciably and seems to be dependent on the thermal history of each individual meteorite. Moreover, inside Ni-rich rhabdite crystals small monocrystalline inclusions of CrN (carlsbergite) have been detected.
Dynamical simulation of electron backscatter diffraction (EBSD) patterns of imperfect crystals
(2012)
Electron microscopy investigation of the structure of a compact extruded from nanopowder of nickel
(2007)
The crystallographic orientation of carlsbergite (CrN) in the north Chile meteorite (hexahedrite) was investigated using electron backscatter diffraction and transmission electron microscopy. These studies examined the CrN crystals in the rhabdites (idiomorphic schreibersite) and in kamacite. It was found that the CrN crystals embedded in rhabdite show a number of different orientation relationships with the host crystals. These orientations can be explained based on the lattice dimensions of both coexisting crystalline materials. It was also found that both carlsbergite and kamacite are characterized by a high dislocation density (109 cm2) while rhabdite is free of dislocations. It is supposed that in spite of the deformed metallic matrix, a general connection between the orientation relation of all the phases involved exists.
Electron backscatter diffraction and energy-dispersive X-ray spectrometry were used to investigate the intermixed interface produced during laser cladding of a Co-Cr-Mo alloy on a steel substrate. A multi-component system and rapid solidification conditions together lead to a complex microstructure at the interface. The solidification of the cladding starts with the formation of an interface layer, which is about 75µm in thickness and consists of randomly oriented equiaxed grains of Co-Cr-Fe solid solution and martensite. Orientation analysis of the grains in the interface layer revealed that some grains have a special orientation relationship with the former austenite grains in the heat affected zone but the cladding is not formed by epitaxial growth on the substrate. Intermixing of the materials at the interface is providing a strong bond between the substrate and the cladding. For a grain from the interface layer to emerge as columnar grain in the cladding, it was determined that its <001> crystallographic direction is not supposed to deviate more than 25° from the sample normal direction.
The high sample tilt angle commonly necessary for an orientation determination by EBSD (electron back-scatter diffraction) is responsible for some simple geometrically caused, but nevertheless essential, image distortions. First of all, the influence of the tilt correction and also the trapezium distortion which appears at low magnifications will be discussed. In the second part, an additional rhomboidal distortion will be introduced which is independent of the magnification used. This distortion appears if the scanned sample surface is out of plane to the tilted stage. Even a small deviation from the parallelity produces an approximately three times bigger error of the Euler angle φ1 when the sample alignment is based on the image captured from the highly tilted sample. This effect especially
concerns small samples (e.g. FIB-lamellae) since they cannot be exactly aligned, but the measurements of bigger samples can also be influenced. As an example a correction procedure is described in detail, based on a repetition of the measurement after a 180° sample rotation.
The role of alpha- to epsilon-Co phase transformation on strain hardening of a Co-Cr-Mo laser clad
(2007)
A laser clad CoCrMo alloy has been analysed by the electron backscatter diffraction (EBSD) technique to examine the microstructural evolution during tensile deformation and to study the role of the evolved microstructure on strain hardening of the clad. The allotropic phase transformation from α- to ε-Co, that did not take place during cooling from the solidification temperature, occurs in the form of a strain-induced transformation during plastic deformation. Combined slip on non-parallel planes in parallel bands of α- and ε-Co prevents the formation of cracks and contributes to the strain hardening of the material. Due to twin formation at intersecting ε-Co bands, {1 1 0 1} planes become almost parallel to {1 1 1} planes of α-Co, and facilitate further glide of dislocations. Owing to the strain-induced transformation of α- to ε-Co, the laser clad CoCrMo investigated in this study can accommodate high deformation before cracks are formed at the wavy slip-lines and the precipitates.
FIB Milling and Canneling
(2007)
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.
A Co-Cr-Mo laser cladding applied on railway wheels is characterised by a combination of EBSD and EDX. A complete pass of the cladding is investigated to achieve a better understanding of the microstructure evolution during laser cladding. A microstructure with columnar grains extending over the whole thickness of the cladding is observed. The grains have a <001>-fibre texture with the fibre axis parallel to the normal of the substrate surface, and a substructure consisting of cells/dendrites. During the cladding process, two different kinds of precipitates form in the cell walls, which can be identified as M6C and a non-equilibrium phase. Furthermore, stacking faults are observed to occur in the cladding grains and are discussed with respect to the laser cladding process.