Showing papers on "Electron backscatter diffraction published in 2003"

Analysis of different acicular ferrite microstructures in low-carbon steels by electron backscattered diffraction. Study of their toughness behavior

Abstract: Acicular ferrite formation, promoted by the intragranular nucleation of ferrite plates, is well known to be beneficial for achieving a good combination of mechanical properties. However, the set of microstructures that can be obtained during the subsequent development of the transformation from the primary plates generated at particles can be quite complex and depends on a certain number of variables: steel composition, temperature range, prior austenite grain size, and particle density. In the present work, acicular ferrite microstructures have been produced by isothermal treatments in three different steels with different active particle types and densities. The morphology of the obtained intragranular microstructures has been found to depend on the steel composition, the prior austenite grain size, and the density of particles able to promote intragranular nucleation. Electron backscattered diffraction (EBSD) techniques have been used to define the microstructural unit controlling toughness in these types of microstructures.

Crystal and domain structure of the BiFeO3-PbTiO3 solid solution

Abstract: X-ray diffraction and transmission electron microscopy have been performed on samples in the solid solution series (BiFeO3)x–(PbTiO3)1−x in which a morphotropic phase boundary occurs at x≈0.7. BiFeO3 exhibits superlattice reflections at 12{hkl}p positions in some electron diffraction patterns, the distribution of which unambiguously demonstrates that the FeO6 octahedra are rotated in anti-phase about the pseudocubic [111] axis, consistent with the rhombohedral (R) space group R3c. The amplitude of the rotations decreases in the R phase as PbTiO3 content increases and superlattice reflections are absent in electron diffraction patterns from the tetragonal (T) phase (x=0.6), indicating that it is untilted with space group P4mm. Electron diffraction patterns from samples where x=0.7 reveal superlattice reflections not associated with octahedral rotations and consistent with an intermediate phase with lower symmetry than T and R.

Structure determination of individual single-wall carbon nanotubes by nanoarea electron diffraction

Abstract: In this letter, we report an electron diffraction determination of chiral vectors (n,m) of individual single-wall carbon nanotubes (SWNTs). Electron diffraction patterns from individual SWNTs were recorded on imaging plates using a parallel electron beam over a section of tube of ∼50 nm long. Using two tubes of 1.39 and 3.77 nm in diameter, we show that the details of electron diffuse scattering can be detected for both the small and large tubes. The quality of diffraction patterns allows the accurate measurement of both the diameters and chiral angles of SWNTs for a direct determination of chiral vectors. The electron diffraction technique is general and applicable to other forms of individual nanostructures.

Introduction to two-dimensional X-ray diffraction

Abstract: Two-dimensional X-ray diffraction refers to X-ray diffraction applications with two-dimensional detector and corresponding data reduction and analysis. The two-dimensional diffraction pattern contains far more information than a one-dimensional profile collected with the conventional diffractometer. In order to take advantage of two-dimensional diffraction, new theories and approaches are necessary to configure the two-dimensional X-ray diffraction system and to analyze the two-dimensional diffraction data. This paper is an introduction to some fundamentals about two-dimensional X-ray diffraction, such as geometry convention, diffraction data interpretation, and advantages of two-dimensional X-ray diffraction in various applications, including phase identification, stress, and texture measurement.

An automated method to determine the orientation of the high-temperature beta phase from measured EBSD data for the low-temperature alpha-phase in Ti–6Al–4V

Abstract: A method was developed to determine the orientation of the high-temperature beta phase from measured electron-backscatter diffraction (EBSD) data for the low-temperature alpha phase in Ti-6Al-4V. This technique is an improvement over existing methods because it does not require a priori knowledge of the variant selection process and can accommodate variants from adjacent beta grains being incorporated in the data set submitted for analysis. It is a general method and therefore can be used to examine texture relationships in materials other than Ti-6Al-4V which undergo a burgers-type phase transformation.

Structure of Ti2P solved by three-dimensional electron diffraction data collected with the precession technique and high-resolution electron microscopy.

Abstract: The crystal structure of Ti2P has been analysed using electron diffraction and high-resolution electron-microscopy techniques. A new unit cell was found, the compound is hexagonal with a = 19.969 (1) and c = 3.4589 (1) A. The structure was first solved in space group P{\bar6}2m in projection using direct methods on electron diffraction data from the [001] zone axis. A three-dimensional solution was obtained using again direct methods but on a three-dimensional set of electron diffraction data recorded with the precession technique. Ti2P is a distorted Fe2P structure and, based on high-resolution images, it is possible to explain that the tripling of the unit cell is due to the ordering of P vacancies that reduces the symmetry to P\bar6.

Effects of Nb on strain induced ferrite transformation in C–Mn steel

Abstract: Effects of the Nb addition on the strain induced ferrite transformation just above Ar 3 temperature were investigated. Hot compression tests were performed with varying the true strain up to 1.6 (80% reduction) using Gleeble 1500. After the hot deformation, samples were immediately water-quenched to examine ferrite formation characteristics. The grain boundary misorientation angles were measured by electron backscatter diffraction in order to observe evolution of the ferrite grains. For reheating temperatures such as 900 and 1000 °C, where Nb was mostly precipitated as NbC, strain induced ferrite grains of 1–2 μm were formed homogeneously within the austenite grain in Nb steel. In the cases of higher reheating temperatures 1100 and 1250 °C, where most of Nb was dissolved, the strain induced ferrite transformation was remarkably reduced and the ferrite morphology was changed to elongated grains. It was considered that the ferrite transformation during deformation was retarded by both the solute drag effect of Nb and the consumption of strain energy for the dynamic precipitation of NbC.

The evolution of annealing textures in 90 Pct drawn copper wire

Abstract: An electrolytic copper rod was drawn in 24 passes to a 90 pct reduction in area and subsequently annealed under various conditions. The global texture of the drawn wire, as measured by X-ray methods, showed a fiber texture approximated by a strong 〈111〉 and a weak 〈100〉 component. However, its microtexture, as measured by electron backscattered diffraction (EBSD), indicated that the major 〈111〉+minor 〈100〉 duplex fiber texture was dominant only in the center region, while a relatively diffuse texture developed with a somewhat higher density of orientations having a 〈11w〉//wire axis in the middle and surface regions. The inhomogeneous texture in the as-deformed wire gave rise to an inhomogeneous microstructure and texture after annealing. When annealed at 300 °C or 600 °C for 3 hours, the wire developed a duplex fiber texture consisting of major 〈100〉+minor 〈111〉 components in the center region, a strong 〈100〉 fiber texture in the middle region, and a weak texture consisting of 〈111〉 and 〈100〉 components with the 〈111〉 component being slightly stronger in the surface region. When the drawn wire was annealed at the high temperature of 700 °C, the texture at short annealing times was similar to that of the wire annealed at the lower temperatures of 300 °C and 600 °C for 3 hours, but prolonged annealing gave rise to a texture ranging from the 〈111〉 to 〈112〉 components due to abnormal grain-growth that started in the surface region. The recrystallization texture consisting of the major 〈100〉+minor 〈111〉 components was explained by the strain-energy-release maximization (SERM) model, in which the recrystallization texture is determined such that the absolute maximum principal stress direction due to dislocations in the deformed state is along the minimum elastic-modulus direction in recrystallized grains. On the other hand, the abnormal grain-growth texture was attributed to grain-boundary mobility differences between differently oriented grain.

Large-scale synthesis of SnO2 nanobelts

Abstract: Tin dioxide (SnO2) nanobelts have been successfully synthesized in bulk quantity by a simple and low-cost process based on the thermal evaporation of tin powders at 800 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal that the nanobelts are uniform, with lengths from several-hundred micrometers to a few millimeters, widths of 60 to 250 nm and thicknesses of 10 to 30 nm. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and selected-area electron diffraction analysis (SAED) indicate that the nanobelts are tetragonal rutile structure of SnO2. The SnO2 nanobelts grow via a vapor–solid (VS) process.

Charge density and chemical bonding in rutile, TiO2.

Abstract: The low-order structure factors of rutile (TiO(2)) have been measured with an accuracy of up to 0.09% by quantitative convergent-beam electron diffraction (QCBED). This error is an order of magnitude smaller than that in conventional Bragg X-ray diffraction and equivalent to the accuracy of the X-ray Pendellosung method. It is sufficient to distinguish atomic, covalent and ionic bonding. By refinement of the combined data of low-order reflections measured by electron diffraction with high-order reflections from X-ray diffraction, accurate charge-density maps are obtained and used to understand the role of the 3d electrons in Ti-O bonding. The results are combined with electron energy-loss spectra (EELS) in a study of the electronic structure.

Grain Boundary Junctions in Microstructure Generated by Multiple Twinning

Abstract: The microstructure of a Cu-Ni alloy after static recrystallization was investigated using electron backscatter diffraction in a scanning electron microscope and the existence of orientationally related clusters of crystallites formed by multiple twinning has been established. Grain boundary and triple junction character within the clusters are analyzed. While the outer boundaries of the cluster are crystallographically random, all the inner boundaries have Σ 3n misorientations. A newly developed crystallographic theory of triple junctions and multicrystallite ensembles consisting of CSL boundaries is used to describe the structure of the cluster. The presence of an α ≠ 1 triple junction is confirmed. Apparently, the microstructure of recrystallized materials susceptible to annealing twinning consists of multiple-twinned clusters. The cluster size cannot be reduced to the “grain size excluding twins.”

Formation of (100)-textured Si film using an excimer laser on a glass substrate

Abstract: We investigated the texture of excimer-laser crystallized Si film For the first time, Si thin films with more than 96% (100) texture have been produced using excimer-laser crystallization of a-Si on a glass substrate The (100) textured film has rectangular grains with edges parallel to the (110) direction Results of scanning electron microscopy (SEM), electron backscatter diffraction patterns (EBSP), X-ray diffraction and transmission electron microscopy (TEM) are presented The results are interpreted on the basis of Si/SiO2 interface energy and a new grain-selection model

Rings of Double-Walled Carbon Nanotube Bundles

Abstract: Rings composed of double-walled carbon nanotubes coherently packed in a triangular arrangement are observed and characterized by transmission electron microscopy (TEM) and electron diffraction. Our conclusions are based on the interpretation of the real space images obtained by TEM and on the analysis of selected area electron diffraction patterns with the help of the kinematic theory of diffraction.

Influence of texture on twin boundary cracks in fatigued austenitic stainless steel

Abstract: It is well-known that crack initiation in fatigued austenitic steel (316L) specimens is dominated at lower deformation amplitudes by twin boundaries (TBs). For medium plastic strain amplitudes, it is shown here that the propagation of short cracks starting at TBs can be explained when both the surface tractions caused by elastic anisotropy as well as the related slip processes are considered. This conclusion has been obtained from grain orientation measurements along damaged TBs using the electron backscatter diffraction technique in the scanning electron microscope. The frequency of the damaged TBs strongly depends on the meso-texture given by the distribution of 60° 〈111〉 rotation axes of the twins in the pole figure. The texture was determined by automatic orientation mapping. Specimens, which were machined transverse to the rolling direction of the plate, show more damaged TBs than those machined parallel. Consequently, the risk of TB cracks can be reduced by favorable alignment of the specimens with respect to the rolling direction.

Effects of grain size on fracture toughness in transition temperature region of Mn–Mo–Ni low-alloy steels

Abstract: An investigation was conducted into the effect of grain size on fracture toughness in the transition temperature region of Mn–Mo–Ni low-alloy steels used for nuclear pressure vessels. Three kinds of steels with different austenite grain sizes (AGS) were fabricated by varying the contents of Al and N, and their microstructures and mechanical properties were examined. Elastic–plastic cleavage fracture toughness, K Jc , was determined by three-point bend tests of precracked Charpy V-notch (PCVN) specimens according to ASTM E1921 standard test method. When the AGS decreased, the total number of carbides increased, while the size and the aspect ratio of carbides decreased. Local fracture stresses, estimated from a theoretical stress distribution in front of a crack tip, were found to be mainly determined by the 92nd% size of carbides. Cross-sectional areas beneath fracture surfaces were observed to understand microstructural features to affect the cleavage crack propagation behavior. The results showed that measured cleavage fracture units were smaller than AGSs, indicating that packet boundaries as well as austenite grain boundaries played an important role in the cleavage crack propagation. Based on the electron back-scatter diffraction (EBSD) results, the cleavage fracture units could also be matched with the effective grain sizes determined by the misorientation tolerance angle of 25°.

Effect of grain orientation on the nitriding rate of a nickel base alloy studied by electron backscatter diffraction

Abstract: Electron backscatter diffraction is a rather new and powerful technique that provides local orientation. In this paper we present an investigation on cross-sections of a nickel base alloy (Inconel 690) treated by low temperature plasma assisted nitriding. The studied alloy presents non-uniform nitrided layer thickness from grain to grain. A linear relationship is found between the thickness of the nitrided layer within a surface grain and the minimum angle between nitriding direction and the 〈1 0 0〉 crystal direction. This angle characterizes the orientation of the grain beneath the nitrided layer. Deeper diffusion is observed in grains with orientation close to 〈1 0 0〉 than in those grains with orientation close to 〈1 1 1〉. An anisotropic dependence of the stress on the strain is proposed to explain these phenomena. The consequences of the interpretation of X-ray diffraction pattern and nitrogen depth profiles of the nitrided layer are discussed.