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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.
Investigation of the orientation relationships of carlsbergite in the North Chile iron meteorite
(2005)
Dynamical simulation of electron backscatter diffraction (EBSD) patterns of imperfect crystals
(2012)
A new technique for investigation of interfacial dislocations in nickel-base superalloys by scanning electron microscopy is presented. At high temperatures the pressure of interfacial dislocations against the γ/γ'-interface causes grooves. This 'fingerprint of the dislocation network' is visualized by deep selective etching, which removes the γ'-phase down to the γ/γ'-interface. Compared with transmission electron microscopy, the proposed method has important advantages: observation of large sample areas, no superposition of dislocations lying in different specimen depths, possibility of three-dimensional view of dislocation configurations, information about the dislocation mobility, reduced time for preparation and visualization. The method can be applied for multiphase materials where the interface is grooved by interfacial dislocations.
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.