Individual Orientation Measurements Research Articles

Local texture and back-end defect in hot extruded AZ91 magnesium alloy

Abstract Local texture in hot extruded MgAl9Zn1 alloy has been studied using individual grain orientation measurement (BKD, “Automated EBSD”) in the SEM. In the shaft of a partial extrudate through a circular die orifice, a <0001> ring fiber texture has formed which continuously changes into a spiral fiber texture in the bottom neck. The flow tube of the internal back-end extrusion defect has a distinctly different texture whereby the (0002) lattice planes are preferentially aligned parallel to the radial and the extrusion directions. The formation of this texture is explained by basal glide, the pile-up of the hard billet mantle, and the inhomo-geneous metal flow during the extrusion process.

Drivers of Student Entrepreneurial Intention and the Moderating Role of Entrepreneurship Education: Evidence from an Indian University

This study is an effort for measuring the entrepreneurial orientation of the students and its linkage with their entrepreneurial intention. The study is based on entrepreneurial dimensions such as innovativeness, need for achievements, opportunity recognition, risk‐taking propensities, and entrepreneurship education. The study also used entrepreneurship education and gender as moderating variables. A 5‐point Likert‐type scale was designed by adapting the Individual Entrepreneurial Orientation measurement scale and Entrepreneurial Intention Questionnaire (EIQ). The authors postulated 7 hypotheses. Data analysis confirmed that underlying entrepreneurial dimensions have a positive correlation with students’ entrepreneurial intention. This paper concludes that entrepreneurial dimensions and proper delivery of entrepreneurship education will help the students in transforming their entrepreneurial intention into actual entrepreneurial action.

Enhancing individual entrepreneurial orientation measurement using a metacognitive decision making-based framework

Entrepreneurship, and individuals’ predisposition toward entrepreneurial activities in particular, i.e. Individual Entrepreneurial Orientation (IEO), has been gaining increasing relevance in academia and management practice alike. Understanding IEO is a critical element not only for its promotion, but for better and more informed managerial and investor decision making as well. As such, this study proposes a new framework for understanding and measuring IEO based on the integrated use of cognitive mapping and the interactive multiple criteria decision making (TODIM) method. We present the steps for building such a framework, as well as a practical application of these steps. The results are promising: the methodology applied allowed a large number of determinants of IEO and their relationships to be mapped; and, subsequently, ranked and weighted for the creation of an IEO measurement tool. The implications of the resulting framework for theory and practice, its limitations and possibilities for further research are also discussed.

Evaluating Deformation-Induced Grain Orientation Change in a Polycrystal During In Situ Tensile Deformation using EBSD.

Using an in situ load frame within a scanning electron microscope, a microstructural section on the surface of an annealed tantalum (Ta) polycrystalline specimen was mapped at successive tensile strain intervals, up to ~20% strain, using electron backscatter diffraction. A grain identification and correlation technique was developed for characterizing the evolving microstructure during loading. Presenting the correlated results builds on the reference orientation deviation (ROD) map concept where individual orientation measurements within a grain are compared with a reference orientation associated with that grain. In this case, individual orientation measurements in a deformed grain are measured relative to a reference orientation derived from the undeformed (initial) configuration rather than the current deformed configuration as has been done for previous ROD schemes. Using this technique helps reveal the evolution of crystallographic orientation gradients and development of deformation-induced substructure within grains. Although overall crystallographic texture evolved slowly during deformation, orientation spread within grains developed quickly. In some locations, misorientation relative to the original orientation of a grain exceeded 20° by 15% strain. The largest orientation changes often appeared near grain boundaries suggesting that these regions were preferred locations for the initial development of subgrains.

Investigations of Fine Grained Metallic Materials by Means of Orientation Maps in Transmission Electron Microscope

New subdivision of microscopic investigation called Orientation Microscopy (OM) is already well known in scanning electron microscope (SEM). Needs for investigation in nanoscale contribute to development of an appropriate method for transmission electron microscope (TEM). Automated acquisition and indexing of diffraction patterns, necessary for creation of orientation maps in TEM, cause more difficulties then in SEM. Nevertheless, the techniques of OM are also being developed in the Transmission Electron Microscope (TEM). Microdiffraction has been successfully introduced for creating such maps. Individual orientation measurements, which appeared in the convergent beam mode, can be used for quantitative description of microstructure of fine grained and deformed materials. The idea of the operation of the automated system in transmission electron microscope (TEM) which is developed in IMIM PAS relies on an automatic (with control position of the beam) acquisition of diffraction patterns using digital CCD camera, and indexing them, and then on the analysis of the set of individual crystallographic orientations. The graphic presentation of received sets of orientation can be analysed in order to obtain parameters and characteristics such as texture characteristics, characteristics of grain boundaries (based on orientation relationship) or the stereological characteristics. To illustrate application of this system, orientation maps measured in cold-rolled polycrystalline aluminium and its alloy 6013, and in multi-phase alloys of Fe-Cr-Co system after severe plastic deformation are presented.

Orientation Distribution Within a Single Hematite Crystal

While crystallography conventionally presumes that a single crystal carries a unique crystallographic orientation, modern experimental techniques reveal that a single crystal may exhibit an orientation distribution. However, this distribution is largely concentrated; it is extremely concentrated when compared with orientation distributions of polycrystalline specimen. A case study of a deformation experiment with a single hematite crystal is presented, where the experimental deformation induced twining, which in turn changed a largely concentrated unimodal “parent” orientation distribution into a multimodal orientation distribution with a major mode resembling the parent mode and three minor modes corresponding to the progressive twining. The free and open source software MTEX for texture analysis was used to compute and visualize orientations density functions from both integral orientation measurements, i.e. neutron diffraction pole intensity data, and individual orientation measurements, i.e. electron back scatter diffraction data. Thus it is exemplified that MTEX is capable of analysing orientation data from largely concentrated orientation distributions.

Texture Analysis with MTEX – Free and Open Source Software Toolbox

The MATLAB™ toolbox MTEX provides a unique way to represent, analyse and interpret crystallographic preferred orientation, i.e. texture, based on integral (“pole figure”) or individual orientation (“EBSD”) measurements. In particular, MTEX comprises functions to import, analyse and visualize diffraction pole figure data as well as EBSD data, to estimate an orientation density function from either kind of data, to compute texture characteristics, to model orientation density functions in terms of model functions or Fourier coefficients, to simulate pole figure or EBSD data, to create publication ready plots, to write scripts for multiple use, and others. Thus MTEX is a versatile free and open-source software toolbox for texture analysis and modeling.

A Comparison of Textures Measured Using X-Ray and Electron Backscatter Diffraction

Shortly after the initial development of an automated technique for measuring individual crystallographic orientations using electron backscatter diffraction (EBSD), several studies were undertaken to estimate the number of single orientation measurements necessary to achieve the statistics of more conventional texture measurement techniques such as pole figure measurement using X-ray diffraction. Since those early studies, the speed of modern EBSD systems has increased by nearly two orders of magnitude. Thus, the question of statistical reliability relative to X-ray diffraction measurements deserves revisiting. This investigation reconsiders the statistical variances between textures measured using individual orientation measurements and those measured using X-ray diffraction. In particular, textures measured by EBSD and X-ray diffraction in rolled stainless steel and in threaded steel rods are compared. Using comparisons of intensities in the orientation distribution functions (ODFs), volume fractions of key texture components and observed sample symmetry suggest that approximately 10,000 grain orientations need to be sampled in these materials of moderate texture strength.

The relationship between the fracture toughness and grain boundary characteristics in hot-dip galvanized zinc coatings

This publication presents an experimental study on the relation between the grain boundary (GB) characteristics and the intergranular cracking resistance in a hot dip zinc coating. The cracking was studied using in situ tensile tests in a scanning electron microscope on small tensile samples of a hot dip galvanized steel sheet. In situ testing offered a series of advantages like monitoring the kinematical evolution of cracking without unloading, or making micrographs and OIM imaging on the same area of the tensile sample. The grain boundaries were classified into random and special boundaries (respectively Low angle boundaries and Coincidence site lattice—CSL boundaries). These special boundaries which account for 3.5% of the whole boundaries clearly show better cracking resistance than the random boundaries. The only special boundaries which present cracking failure are in an orientation with their normal direction close to the tensile direction, i.e. submitted to a maximum effective stress. The grain boundaries characteristics are obtained from EBSD individual orientation measurements.

Neutron Diffraction Texture Analysis

An intrinsic property of polycrystalline materials is the orientation distribution of crystallites. In some cases this distribution is random, yet often there is preferred orientation of crystallites relative to macroscopic axes that may have been attained during a deformation process. Many rocks—metamorphic, igneous as well as sedimentary—display non-random orientation distributions that are the cause for anisotropy of macroscopic physical properties. Interpretation of textures in materials has to rely on a quantitative description of orientation characteristics. Two types of preferred orientations need to be distinguished: The shape preferred orientation (or often abbreviated SPO) describes the orientation of grains with anisotropic shape. The lattice preferred orientation (LPO) or “texture” refers to the orientation of the crystal lattice. (LPO is an unfortunate term since the lattice does not always uniquely describe the crystal orientation, as in the trigonal mineral quartz with a hexagonal unit cell. “Crystallographic preferred orientation,” CPO, would be more appropriate). Shape and crystal orientation can be correlated, such as in sheet silicates with a flaky morphology in schists, or fibers in fiber reinforced ceramics. In other cases they are not. In a rolled cubic metal or a plastically deformed quartzite, the grain shape depends on the deformation and is not directly related to the crystallography. Many methods have been used to determine preferred orientation. Geologists have applied extensively the petrographic microscope equipped with a Universal stage to measure the orientation of morphological and optical directions in individual grains (e.g., Wahlstrom 1979; Wenk 1985). More recently electron diffraction, both with transmission (TEM) and scanning electron microscopes (SEM) have been used to measure orientation of crystals (e.g., Schwarzer and Weiland 1988; Randle and Engel 2000). In this case, the location of a grain can be determined, which permits to correlate microstructures, neighbor relations and texture. Also from individual orientation measurements …

Local texture and back-end defect in hot extruded AZ91 magnesium alloy

Abstract Local texture in hot extruded MgAl9Zn1 alloy has been studied using individual grain orientation measurement BKD, “Automated EBSD”! in the SEM. In the shaft of a partaal extrudate through a circular die orifice, a ring fiber texture has formed which continuously changes into a spiral fiber texture in the bottom neck. The flow tube of the internal back-end extrusion defect has a distinctly different texture whereby the (0002) lattice planes are preferentially aligned parallel to the radial and the extrusion directions. The formation of this texture is explained by basal glide, the pile-up of the hard billet mantle, and the inhomogeneous metal flow during the extrusion process.

Texture in Hot Extruded, Hot Rolled and Laser Welded Magnesium Base Alloys

In this work the textures of MgAl9Zn1, MgAl6Zn1, MgAl3Zn1 and MgAl2Mn alloys have been studied, using individual grain orientation measurement (“ACOM”) in the SEM. Hot extruded billets, unidirectional, reverse and cross-rolled sheet metals as well as laser welding seams have been investigated. In the shaft of a partial extrudate through a circular die orifice, a <0001> ring fiber texture has formed which continuously changes into a spiral fiber texture in the bottom neck. The unidirectional and the reverse hot rolled MgAl2Mn specimens show an R type <0001> texture with a small asymmetrical split whereby the basal poles are tilted by about ±12° from the sheet normal direction to the rolling direction. In the hot cross rolled specimens, the basal poles are slightly spread both in the first and second rolling directions. Texture in the laser welding seams is weak and distinctly different from that of the sheet material. There is almost no heat affected zone at the margins of the welding seams.

Determination of Texture from Individual Grain Orientation Measurements

We present a technique for determining the texture of a polycrystalline material based on the measurement of the orientation of a number of individual grains. We assumed that the sample has fiber (i.e., axisymmetric) texture and that the texture can be characterized by a function (the March-Dollase function) with a single parameter. We simulated a large number, N, of orientation data sets, using the March-Dollase function for a total of five different texture parameters, rinit. Using the maximum-likelihood method, we solved for the texture parameter, r´, that best fits each simulated data set in order to determine the distribution of r´ and evaluate the precision and accuracy with which r´ can be determined. The 90% confidence limits of the ratio r´/rinit vary as N-1/2 but were independent of rinit. Using the texture of slightly textured Al2O3 as determined by X-ray diffraction, we calculated the 90% confidence limits for measurements of 131 grains. The orientations of 131 grains in textured Al2O3 were measured by electron backscatter diffraction, and the texture determined from those measurements lay within these 90% confidence limits.

A methodology for measuring and modeling crystallographic texture gradients in processed alloys

Abstract The explicit representation of internal material structure in alloy processing and in-service performance simulations is becoming increasingly prevalent. This paper presents a methodology for characterizing and representing a spatially-varying orientation distribution function (ODF) that can be used in processing and performance simulations for alloys containing texture gradients. We use thick AA 7050 aluminum plate, which is known to contain texture gradients, as a case study to demonstrate the methodology, which employs a finite element representation of the ODF initialized using individual lattice orientation measurements taken using the electron backscatter pattern (EBSP) technique. As expected, we find that the texture varies significantly through the plate thickness. We use the ODF to examine the effect of the varying texture on the resulting yield strength distribution as embodied by the average Taylor factor. We find that the predicted yield strength anisotropy is different at different locations through the thickness of the plate. We examine the optimal number of orientation measurements necessary for determining the ODF in the presence of this texture gradient. We find that as we increase the number of orientations, the ODF quickly becomes stable but eventually starts to change under the influence of the texture gradient. We also investigate spatial interpolation of the ODF using the finite element representation. We find that, as with finite element representations of other fields, interpolation accuracy depends on the variation of the field variable and the discretization of the domain. In this case, gradients in both physical space and orientation space affect the accuracy of the interpolation. Finally, the effects of the texture gradient on the mechanical response of the material is demonstrated by employing the ODFs taken from various locations through the thickness of the plate in polycrystal plasticity simulations of uniaxial tension and plane strain compression.

Feldspar fabrics in a greenschist facies albite-rich mylonite from electron backscatter diffraction

The current database of plagioclase CPOs in naturally deformed rocks is small and is not supported by CPOs from experimentally deformed rocks or by numerical modelling so that the current understanding of plagioclase CPOs is limited. Electron backscatter diffraction (EBSD) has the potential of measuring the full crystallographic orientation of small domains of any crystalline material, including plagioclase. We generate and test a file of the relative electron diffraction intensities for lattice planes in the albite structure. This enables rapid and accurate individual orientation measurements of albite, using EBSD. EBSD is used to collect 360 data points from 7 areas across a 2 cm by 1 mm pure albite band in a greenschist-facies, albite mylonite from a gabbro protolith. The CPOs are unlike any published. The [ a]-, [ b]- and [ c]-axes of albite are not symmetrically distributed with respect to the kinematic axes of deformation and do not possess an internal monoclinic or orthorhombic symmetry. There is some microstructural evidence for the operation of dislocation creep, although this interpretation conflicts with the generally held view that crystal plastic deformation does not occur in plagioclase below about 500°C. An alternative mechanism is one of granular flow accommodated by solution transfer. However, this mechanism would be expected to give a random CPO. For either mechanism we need to explain the triclinic nature of the CPO. It is possible that the CPO represents the modification by deformation of a pre-existing CPO, probably defined by a small number of original plagioclase grains.

Local crystal textures: experimental techniques and future trends

Transmission electron microscopy enables crystal textures to be determined in small specimen areas by measuring SAD or RHEED pole figures. SAD (transmission) pole figures are acquired either by deflecting the diffraction patterns or the primary beam along a cone of 2 · Θ semi-apex angle, or by grabbing the whole diffraction patterns with a CCD camera. RHEED pole figures are obtained from the bulk surface by rotating, at grazing beam incidence, the specimen about its surface normal and grabbing a sequence of RHEED patterns. Since the specimen has to be tilted through large angles, spatial resolution is limited to 1.5 μm in SAD and to 0.1 mm in RHEED pole figure measurement. The major benefits over x-ray diffraction are a high speed and sensitivity. Spatial resolution of individual grain orientation measurement is in the range of 0.1 μm in the SEM with backscatter Kikuchi patterns (BKP) from the bulk, respectively 10 nm in the TEM with transmission Kikuchi patterns (TKP). Using a computer controlled SEM and digital beam scan, more than 10,000 grain orientations per hour are acquired unattendedly. Crystal orientation maps (COM) are constructed by a pseudo-color representation of the individual orientations in the area under study. An x-ray scanning apparatus with energy dispersive spectrometer enables the acquisition of texture as well as element distribution (X-ray microfluorescence analysis) maps at a spatial resolution of some 10 μm.

Sampling Error of Texture Approximation by Individual Orientation Measurement

The reliability of the ODF obtained from individual orientation measurement is usually limited by the finite number of data points rather than by the experimental angular resolution which is usually better than 1°. Hence measures of confidence of relevant distribution parameters are highly demanded for texture interpretation. Starting from the multinominal distribution, estimates of the empirical density distribution function and the C coefficients as well as their variances are given. Furthermore estimates of the optimum 1 value for series truncation and reasonable choices of smoothing parameters can be derived from the standard deviations of the C coefficients. Computer simulations on model textures have been carried out to confirm the results. The empirical distribution parameters as a function of sample number are in good accord with those predicted by theory.

In Situ Recrystallization of Copper Studied by Individual Grain Orientation Measurement in the SEM

The effect of orientation and misorientation of the individual grains on the recrystallization behavior of deformed copper is investigated. Samples of pure copper which were cold rolled to 95% reduction are annealed in several steps under observation in the SEM. A heating stage has been developed which enables long-term heating experiments in the SEM up to 400 °C. The samples are annealed step by step. The same area of specimen surface is studied in subsequent stages of recrystallization. Before and after each annealing treatment the crystallographic orientations of the individual grains are measured by interpreting Backscatter Kikuchi Patterns (BKP) using the Automated Crystal lattice Orientation Mapping (ACOM) device. A comparison of the resulting crystal orientation maps yields the changes of structure and local orientation with progress of recrystallization. Recrystallized areas can be distinguished from areas which are not yet recrystallized. It becomes directly visible which grains are growing at the expense of others.

Processing Indiviual Orientation Data to Calculate ODFs

In order to calculate an ODF from a set of individual orientation measurements, it is very useful at first to characterise the texture type. By using model functions it is shown that the texture index plays a particular role. Moreover it has been found that the texture index varies linearly with the inverse of the number N of measurements. The ODF can then be calculated with the constraint to reach a particular texture index. Various examples are presented.

Automated Crystal Orientation Mapping (ACOM) of Thin Metallization Layers and Interconnects

ABSTRACTA system for acquisition and interpretation of Kikuchi patterns with computer-controlled electron microscopes is presented. It enables interactive as well as fully automated determination of individual grain orientations. Special features for automated crystal orientation mapping (ACOM) with the scanning electron microscope (SEM) are digital beam scan, autocalibration and dynamic focus controlled by the computer. With the present setup about three orientations per second can be measured unattendedly. In the transmission electron microscope (TEM) the on-line determination of Burgers vectors and identification of deformation systems are based on crystal orientation measurement. The characterization of dislocations is facilitated by the simulation of diffraction patterns on the computer as a function of specimen tilt.Crystal orientation maps are obtained by assigning to the raster points in the image a color specific for the grain orientation, the misorientation or character of the grain boundary. The dala set of grain orientations is used to calculate the Schmid factors grain by grain, the orientation distribution function (ODF) and the correlated as well as the uncorrelated misorientation distribution functions (MODF) which characterize crystallographic texture in a statistical sense.Applications of individual grain orientation measurement are:. Thermomechanical hillocks in aluminum metallization layers on silicon substrates. Stress-induced grain growth in aluminum metallization layers on silicon substrates. Electromigration voids and hillocks in aluminum interconnectsA working hypothesis for electromigration failure, based on experimental findings, is discussed