Showing papers on "Electron backscatter diffraction published in 1997"

Combined texture and structure analysis of deformed limestone from time-of-flight neutron diffraction spectra

Abstract: The orientation distribution of a textured polycrystalline material has been traditionally determined from a few individual pole figures of lattice planes hkl, measured by x-ray or neutron diffraction A new method is demonstrated that uses the whole diffraction spectrum, rather than extracted peak intensities, by combining the orientation distribution calculation with the crystallographic Rietveld method The feasibility of the method is illustrated with time-of-flight neutron diffraction data of experimentally deformed polycrystalline calcite It is possible to obtain quantitative information on texture, crystal structure, microstructure, and residual stress from highly incomplete pole figures and from regions of the diffraction spectrum containing many overlapping peaks The approach provides a key for quantitative texture analysis of low symmetry compounds and of composites with complicated diffraction spectra

Advances in texture analysis from diffraction spectra

Abstract: The orientation distribution of a textured polycrystal has been traditionally determined from a few individual pole figures of lattice planes hkl, measured by X-ray or neutron diffraction. A new method is demonstrated that uses the whole diffraction spectrum, rather than extracted peak intensities, by combining ODF calculation with Rietveld crystal structure refinement. With this method, which is illustrated for a synthetic calcite texture, it is possible to obtain quantitative texture information from highly incomplete pole figures and regions of the diffraction spectrum with many overlapping peaks. The approach promises to be advantageous for low-symmetry compounds and composites with complicated diffraction spectra. The method is particularly elegant for time-of-flight neutron diffraction, saving beam time by using small pole-figure regions and many diffractions.

γ-Fibre recrystallization texture in IF-steel: an investigation on the recrystallization mechanisms

Abstract: Development of recrystallization texture in cold-rolled Ti-bearing IF-steel was investigated using X-ray diffraction, Electron Back Scattered Diffraction/Orientation Imaging Microscopy (EBSD/OIM) and TEM. During cold-rolling, both the α (RD//〈110〉) and the γ (ND//〈111〉) fibres were observed to be strengthened, although the increase in α was more pronounced. Simulations of the cold-rolling using Taylor type theories demonstrated an approximate predictability of the textural changes. Recrystallization strengthened the γ, as F (={111}〈112〉) increased but E (={111}〈110〉) remained essentially unchanged. A corresponding decrease in α, more in H (={001}〈110〉) than in I (={112}〈110〉), was also observed. The strong γ-fibre recrystallization texture was mainly due to the larger numbers (i.e. `frequency advantage') of the γ-oriented grains, as the γ grains were no larger than grains of other orientations. TEM studies showed an increase in cell size and a decrease and cell misorientation (which means an increase in stored energy) from H⇒I⇒E⇒F. With the exception of a slight drop from E to F, increase in the Taylor factor always corresponded to an increase in the stored energy. The spread of stored energies, corresponding to inhomogeneities in dislocation substructure, were observed to increase from I⇒H⇒E⇒F. A combination of the higher stored energy and the stronger inhomogeneities in dislocation substructure is possibly responsible for the preferred nucleation behavior causing the frequency advantage for the γ grains.

Electron backscatter diffraction and orientation imaging microscopy

Abstract: An overview of electron backscatter diffraction is presented in which experimental procedures are reviewed together with a basic theoretical description of the mechanism of pattern generation Manual and automated indexing procedures are described The new technique of orientation imaging microscopy is presented, with examples from recrystallised AI-Mg alloy, deformed superplastic material, and fractured nickel base alloy

Diffuse wall structure and narrow mesopores in highly crystalline MCM-41 materials studied by X-ray diffraction

Abstract: Synchrotron X-ray diffraction patterns for highly crystalline MCM-41 a mesoporous silicate molecular sieve are presented. The form factor observed in seven orders of diffraction is used to show the existence of a two-layer wall structure, with a narrower mesopore than previously assumed, and much void space in the walls.

Electron back scattered diffraction (EBSD) analysis of quasi-cleavage and hydrogen induced fractures under cyclic and dwell loading in titanium alloys

Abstract: Evidence for sub-surface fatigue crack initiation is often reported for near alpha titanium alloys such as the coarse grained IMI685 and the fine duplex structured IMI834. In such materials with a typical as received hydrogen concentration of 40–60 ppm the initiation site is invariably characterized by quasi-cleavage facetting. Similar facetting is also associated with the low temperature dwell sensitive fatigue response in the same alloys. For IMI685, it is reported that this failure mechanism is replaced by α/β interface cracking when the alloy contains a relatively high concentration of interstitial hydrogen. The present paper characterises the local grain orientation and microstructural conditions associated with these various forms of failure through the use of a microtextural analysis technique based upon electron back scattered diffraction (EBSD) measurements. The observations are related to an existing model to account for facet formation based upon the pile-up of dislocations at grain-boundaries. The implications for further use of this technique with titanium alloys are discussed.

Time-resolved diffraction

Abstract: 1. Picosecond hard X-ray pulses and their application to time resolved diffraction 2. Ultrafast X-ray diffraction and absorption 3. Laser-plasma X-ray emission: its creation, diagnosis and use in applications 4. X-ray diffraction dynamics of shock-compressed crystals 5. Materials science opportunities using time-resolved synchrotron X-ray scattering 6. Overview of time-resolved macromolecular crystallography 7. Laue and monochromatic technique developments for time-resolved biological and perturbation chemical crystallography 8. Time-resolved protein crystal diffraction: determination by the Laue method of the behaviour of the enzyme hydroxymethylbilane synthase (Lys59Gln mutant) as it is loaded with substrate in the crystal 9. The realization of 100 ps Laue diffraction on ID09 and shortcuts to 100 fs time-resolution in X-ray scattering experiments 10. High performance detectors for time-resolved non-crystalline X-ray diffraction 11. Theory of ultrafast time-resolved X-ray and electron diffraction 12. Time-resolved surface electron diffraction 13. Time-resolved electron diffraction: a method to study the structural and vibrational kinetics of photoexcited molecules 14. Time-resolved electron diffraction and microscopy studies of membrane proteins 15. Pulsed neutron diffraction: new opportunities in time-resolved crystallography

Three‐dimensional reconstruction of Widmanstätten plates in Fe–12.3Mn–0.8C

Abstract: The three-dimensional reconstruction of serial sections is applied to examine Widmanstatten plates in a high-manganese steel. Serial sections were obtained through repeated metallographic polishing and imaging and interpolation was done using the ‘watershed’ algorithm. Electron backscatter diffraction was used to determine grain misorientations and cementite:austenite orientation relationships. This technique yields a unique combination of information concerning crystallography and the three-dimensional development of a solid body.

Holographic Image Reconstruction from Electron Diffraction Intensities of Ordered Superstructures

Abstract: We report on a novel holographic reconstruction of well resolved atomic images from discrete spot intensities appearing in low-energy electron diffraction (LEED) from crystalline surfaces. This opens holographic LEED to the wide field of ordered systems giving access to rather complex surface structures.

Role of the Step Density in Reflection High-Energy Electron Diffraction: Questioning the Step Density Model

Abstract: The step density model of reflection high-energy electron diffraction oscillations is investigated. Within this model, the temporal evolution of the specular beam intensity during growth by molecular beam epitaxy represents the evolution of the step density during deposition. This is found to be inconsistent with diffraction theory. In particular, when the concentration of atoms in the deposited layer is fixed, an increase of the step density causes an increase of the specular beam reflectivity, contrary to the prediction of the step density model.

Electron beam induced crystallization in Fe-doped SnO2 nanoparticles

Abstract: Nanoscale particles of Fe-doped SnO2 were intensively radiated in a high-energy electron beam observed in situ in a transmission electron microscope. Generation of small crystalline grains from agglomerated nanoparticles was observed. Electron diffraction patterns confirmed that the grains belonged to the orthorhombic phase of SnO2, which forms only under pressures higher than 140 kbar according to previous research. A possible process for the phase transition is discussed. The result suggests a novel method of producing orthorhombic SnO2 at low pressure.

Analysis of Grain Colonies in Type 430 Ferritic Stainless Steels by Electron Back Scattering Diffraction (EBSD)

Abstract: Ridging is a serious problem which occurs in ferritic stainless steel after tensile deformation in the rolling direction, and steel makers are attempting to respond to the surface deterioration caused by this phenomenon. Many authors have suggested that a long distance order in the lattice orientation of a sheet could be responsible for ridging. In this study, the authors performed local orientation measurement on two samples of type 430 stainless steel using orientation imaging microscopy, and analyzed the grain orientations of the RD and ND planes. Data on areas covering more than 5mm 2 are presented here for the first time in the literature. The experimental results prove the existence of grain bands in the ND plane of samples with severe ridging. However, the texture maps for the RD planes are in disagreement with many previously proposed theories. Therefore, a new mathematical model is introduced. The simulated ridging profiles of the samples calculated with this new model agree with the experimental results. Finally, a method of amelioration that can significantly improve the theoretical model is proposed.

The effect of local textures on microcrack propagation in fatigued f.c.c. metals

Abstract: The individual crystallographic orientation of the grains in fatigued specimens with fcc lattice (nickel and austenitic steel) was determined with the help of electron backscattering diffraction (EBSD) From the orientation data, the misorientation of neighboured grains was calculated (angle-axis pairs) In nickel specimen, twin boundaries are preferred sites for microcrack initiation and propagation The observed damaged twin boundaries agree with Neumann's model of additional incompatibility stresses In austenitic steel, a greater portion of microcracks propagate in random grain boundaries The probability of microcrack propagation can be given by a misorientation crack factor, which takes into account the incompatibility of the grain rotation during the plastic deformation of misoriented grains

The effect of Si on the relationship between orientation and carbide morphology in high chromium white irons

Abstract: Electron back-scatter diffraction (EBSD) has been shown to be the most appropriate technique to study the orientation and carbide morphology of small (<0.5 μm) regions of microstructure of high chromium white irons. The carbides in a slightly hypo-eutectic Fe–Cr–C alloy show a distinct texture close to [1 0 1 1] whereas those in a 1.3 wt% Si commercial white iron have a diffuse texture, with regions near to major crystal directions, i.e., [0 0 1 1], [1 2 1 0], [0 1 1 0], unpopulated. Using EBSD, it has been shown that the interconnectivity of the eutectic (Cr, Fe)7C3 carbide is less in a 1.3 wt% Si alloy compared with a low (0.1 wt%) Si alloy. This reduced interconnectivity is consistent with the increased fracture toughness in the as-cast condition.

Fortuitously Superimposed Lattice Plane Secondary Diffraction from Crystalline Colloidal Arrays

Abstract: Dispersions of monodisperse macroionic spherical particles self assemble into bcc or fcc crystalline colloidal arrays (CCA), which efficiently Bragg diffract light in the near-IR, visible, and UV s...

A new powerful tool for surveying cleavage fracture surfaces

Abstract: — A new tool is presented to investigate cleavage fracture surfaces. It is based on the combined techniques of crystal orientation measurements using the Electron Back-Scatter Diffraction (EBSD)-technique and 3-dimensional surfaces reconstruction by an Automatic Surface Reconstruction System (ASRS). With this tool we can perform crystallographic fractometry of cleavage fracture facets of polycrystals within the limits of the resolution of a Scanning Electron Microscope (SEM), e.g. we can determine the crystallographic indices of cleavage planes and of directions on such planes.

Methods for determining elastic strains from electron backscatter diffraction and electron channelling patterns

Abstract: Two approaches to the measurement of elastic strains from electron channelling patterns (ECPs) and electron backscatter diffraction (EBSD) patterns are assessed. Analysis of the shift in channelling (or Kikuchi) line positions has been shown to yield strain sensitivities of up to 3 parts in 104 when {10 10 O} lines in ECPs are used. The lack of such fine detail in EBSD patterns restricts such methods to strains at least one order of magnitude greater. For EBSD an alternative method is presented in whichelastic strains are determined from measurements of small shifts in zone axis positions. The strain sensitivity of the method was found to be 2 parts in 104. Measurements, using this method, of elastic strains in Si1-xGex epitaxial layers grown on Si substrates gave excellent agreement with X-ray diffraction data. The EBSD technique is capable of determining elastic strain variations at submicrometre resolution.

Picosecond-milliangstrom resolution dynamics by ultrafast x-ray diffraction

Abstract: Optical pump, x-ray diffraction probe measurements have been used to study the lattice dynamics of single crystals with picosecond-milliangstrom resolution by employing a table- top, laser-driven x-ray source. The x-ray source, consisting of an approximately 30 fs, 75 mJ/pulse, 20 Hz repetition rate, terawatt laser system and a moving Cu wire target assembly, generates approximately 5 X 1010 photons (4π steradians s)-1 of Cu Kα radiation. Lattice spacing changes of as small as 1 X 10-3 a in a few picoseconds have been detected, utilizing Bragg diffraction from GaAs single crystals. Enhancement of the diffraction intensity associated with degradation of the crystals during and after the laser irradiation has been observed, likely due to a transition from dynamic to kinematic diffraction.