Electron Backscattered Diffraction (EBSD) with a Cold Held Emission Gun (cFEG) SEM: Resolution, Sensitivity and Applications

Image degradation characteristics and restoration based on regularization for diffractive imaging

Ferroelectric ceramics are widely used in a diverse set of devices including sensors, actuators, and transducers. The technological importance of ferroelectrics originates from their large electromechanical coupling. Ferroelectric materials exhibit a complicated behavior in response to both electrical and mechanical loads which produce large internal stresses that eventually lead to failure. Efforts to model and predict the behavior of ferroelectrics have been hindered by the lack of suitable constitutive relations that accurately describe the electromechanical response of these materials. While many measurements have been conducted on the macroscopic response of single-crystals or polycrystals, multiaxial (and multiscale) data about the in situ internal strain and texture response of these materials is lacking; this information is critical to the development of accurate models, and diffraction techniques which directly measure internal crystal strains and material texture are aptly suited to supply it. A neutron diffraction technique was employed which allowed for the simultaneous measurement of material texture and lattice strains in directions parallel and transverse to an applied mechanical load. By comparing the behaviors of single-phase tetragonal, single-phase rhombohedral, and dual-phase morphotropic compositions, information concerning mechanics of average macroscopic behavior was inferred. In an effort to probe more of the multiaxial constitutive behavior, a high-energy X-ray diffraction technique was employed. Using transmission geometry and a 2-D image plate detector, 36 different directions of sample behavior were measured simultaneously. Polychromatic scanning X-ray microdiffraction was used to investigate the microscale three-dimensional strain tensor in single-crystals. One investigation yielded the first ever direct measurement of the tri-axial strain fields associated with single domain walls in ferroelectrics. The second investigation recorded the domain switching mechanisms activated to accommodate indentation-induced fracture stresses. Finally, 3-D XRD was used to probe the mesoscale constitutive behavior of single, embedded grains of BaTiO3 within a polycrystalline matrix. The experimental methods described in this thesis provide access to two-dimensional and three-dimensional multiaxial constitutive strain behavior in ferroelectrics for each of the microscopic, mesoscopic, and macroscopic length scales. Results from each of these length scales will provide critical data for models attempting to accurately describe the behavior of ferroelectric materials.

There is currently no general agreement on how to extract the volume fraction of texture components for aluminum alloy sheets based on X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) techniques. In order to clarify this problem, grain orientation data of AA5754 sheet material in the O-temper were acquired using XRD and EBSD. The volume fractions of 10 selected texture components were calculated using the MTM FHM software package for XRD and EDAX-TSL OIM Analysis for EBSD. The measured grain orientation data from EBSD were then processed again using MTM FHM. The results show that there are no significant differences in the constructed pole figures using different measuring techniques when the same analysis system is used. Thus, the differences in volume fractions of texture components are mainly related to the deviation angle used in the two different software packages. The differences in the deviation angle used lead to potential overlaps between the selected texture components. A suitable deviation angle for the volume fraction calculation can be selected using the concept of misorientation.

Ten years ago electron backscatter diffraction (EBSD) became available to a wider group active in materials research. This paper highlights some of the more significant developments in camera technology and software developments that have arisen since then. The use of slow-scan charge couple device cameras for phase identification and rapid determination of orientation image micrographs is reviewed. The current limiting spatial resolution of the technique is shown to be less than 10 nm. A procedure for improving lattice spacing measurement by utilizing the full resolution of the camera is described with experimental measurements on silicon and nickel showing relative errors of plus/minus 3%. An investigation of partially recrystallized aluminium shows how the recrystallized fraction can be extracted with confidence but that the mapping of substructure in the highly deformed regions is questionable. Phase identification is described for complex cases in which the phase data tabulated in standard databases do not correspond to what is observed in the EBSD patterns. Phase mapping in a complex mineral in which chemical data and EBSD data are collected simultaneously is shown to be improved by recording both the chemical and the EBSD data into computer memory and proceeding with the phase discrimination and orientation measurement in off-line analysis.

Two methods for measuring dislocation density were applied to a series of plastically deformed tensile samples of Zircaloy-2. Samples subjected to plastic strains ranging from 4 to 17% along a variety of loading paths were characterized using both electron backscatter diffraction (EBSD) and synchrotron X-ray line profile analysis (LPA). It was found that the EBSD-based method gave results which were similar in magnitude to those obtained by LPA and followed a similar trend with increasing plastic strain. The effects of microscope parameters and post-processing of the EBSD data on dislocation density measurements are also discussed. The typical method for estimating uncertainty in dislocation density measured via EBSD was shown to be overly conservative, and a more realistic method of determining uncertainty is presented as an alternative.

Effects of crystal structure and grain orientation on the roughness of deformed polycrystalline metals

Texture evolution of the deep drawing of molybdenum sheet was investigated with EBSD (Electron Back Scattered Diffraction), X-ray diffraction techniques and orientation distribution function (ODF) analysis. The texture during deep drawing is hardly changed due to the strong of initial texture. Specimens symmetry of 45° from rolling direction have monoclinic symmetry during deep drawing proce ss. EBSD can be used for the quantitative determination of macroscopic texture as like X-ray diffraction techniques if a sufficient number of grains are measured. Grain sizes show the similar values during deep drawing process but their values along 45° direction from rolling direction at flange and wall are tend to increase. It is associated with the 45° earing of deep drawing processing. The correlation function values were -0.58 for RD flange and -0.36 for RD wall and suggest that high Taylor factor regions have low pattern quality and low Taylor factor regions have high pattern quality.

Within this research, the multiscale microstructural evolution before and after the tensile test of a FeCo alloy is addressed. X-ray µ-computer tomography (CT), electron backscattered diffraction (EBSD), and transmission electron microscopy (TEM) are employed to determine the microstructure on different length scales. Microstructural evolution is studied by performing EBSD of the same area before and after the tensile test. As a result, langle001rangle||TD, langle011rangle||TD are hard orientations and langle111rangle||TD is soft orientations for deformation accommodation. It is not possible to predict the deformation of a single grain with the Taylor model. However, the Taylor model accurately predicts the orientation of all grains after deformation. {123}langle111rangle is the most active slip system, and {112}langle111rangle is the least active slip system. Both EBSD micrographs show grain subdivision after tensile testing. TEM images show the formation of dislocation cells. Correlative HRTEM images show unresolved lattice fringes at dislocation cell boundaries, whereas resolved lattice fringes are observed at dislocation cell interior. Since Schmid’s law is unable to predict the deformation behavior of grains, the boundary slip transmission accurately predicts the grain deformation behavior.

Pressure vessels comprise critical plant equipment within industrial operations. The fact that the vessel operates under pressure, and may carry toxic, dangerous, or hazardous contents, necessitates that care is taken to ensure safety of humans operating it and the environment within which it operates. Residual stress developed during welding of pressure vessel structures can adversely affects fatigue life (mean stress effect) of such structure and lead to corrosion crack growth. The present study applies the neutron diffraction (ND) technique to formulate the stress field distribution of a nozzle-to-shell weld joint of a pressure vessel. A number of experiments are conducted using the submerged arc welding (SAW) process at various parametric combinations to develop a number of specimens with different stress profiles. It is shown that the hoop stresses close to the weld center line (WCL) are highly tensile and have values close to the yield strength of the material. The ideal parametric combination is also determined based on the results with lowest stresses. The results obtained in this study are congruent to the results of similar studies in the literature.

This paper describes residual stress measurements and analysis of austenitic stainless steel pipe with a butt-welded joint. The measurements were done with neutron diffraction and strain gauge techniques. The measured results had typical characteristics of butt-welded pipe regarding both the decline of stress along the axial direction and the bending distribution of axial stress along the radial direction. The measured residual stress distribution by neutron diffraction was shifted more to the tensile side than that by the finite element method simulation. However, the measured radial and axial strains, except for the hoop strain determined by neutron diffraction, coincided well with analysis strains. The hoop strain was actually equivalent strain converted by a correction method because a different lattice plane had to be used to measure hoop strain. This might be one reason why the difference occurred. Therefore, future study of the correction method would be desirable.

Evaluating quartz crystallographic preferred orientations and the role of deformation partitioning using EBSD and fabric analyser techniques

Improved structural homogeneity and mechanical properties of nanoparticles reinforced Al composites after orthogonal thermomechanical processes

Aluminum thin films deposited onto silicon substrates coated with silicon dioxide or a layered structure of titanium and titanium nitride have been investigated using the combined techniques of electron backscatter diffraction and orientation imaging microscopy. By these methods the local texture and spatial distribution of texture components was established. It was observed that whereas the material exhibited an overall <111> texture with the in-plane direction <110> uniformly distributed, there were variations in the local texture and distribution of orientations with clustering of grains of similar orientation. Individual grains within the clusters were nearly perfect and varied in orientation by only a few degrees. The effective grain size differed greatly on whether the cluster size of similarly oriented grains or the diameter of individual grains within the cluster was considered to constitute the grain structure. No strong bias was found in favor of coincident site oriented grain pairs though in some cases the frequency of occurrence of low angle boundaries was less than is expected on a purely random basis. Additional experiments were carried out in order to establish the suitability of orientation imaging microscopy for microstructure characterization of interconnect lines in integrated semiconductor device technology.

Additive manufacturing has been around for many years, yet the underlying physics of thermal gradients, local pressure environment, and other non-steady state manufacturing conditions are not fully understood. A Multi-University Research Initiative (MURI) is currently ongoing to measure liquid/solid and solid/solid interface stabilities in AM Ti-6Al-4V. Samples were produced with different beamscanning strategies in order to study the role of thermal gradients on the resulting microstructure. The motivation is to determine which beam-scanning strategy leads to desired grain size and texture. Orientation at different length scales (from mm to nm) can be quantified and compared with a combination of techniques including Precession Electron Diffraction (PED), Electron Backscatter Diffraction (EBSD) and Neutron diffraction. This new information will help predict properties of additively manufactured parts.

The electron backscatter diffraction (EBSD) technique enables an advanced analysis of anisotropic materials like ferrites. Here, the spatially highly resolved EBSD mappings provide additional information as compared to the standard analysis techniques, which can contribute to an optimization of the growth process. Furthermore, an analysis of the grain aspect ratio is possible which provides further insight to the microstructural dependence of the magnetic properties of ferrites.