Electron Backscatter Diffraction in Materials Science

Frontmatter

Chapter 1. Present State of Electron Backscatter Diffraction and Prospective Developments

Electron backscatter diffraction (EBSD), when employed as an additional characterization technique to a scanning electron microscope (SEM), enables individual grain orientations, local texture, point-to-point orientation correlations, and phase identification and distributions to be determined routinely on the surfaces of bulk polycrystals. The application has experienced rapid acceptance in metallurgical, materials, and geophysical laboratories within the past decade (Schwartz et al. 2000) due to the wide availability of SEMs, the ease of sample preparation from the bulk, the high speed of data acquisition, and the access to complementary information about the microstructure on a submicron scale. From the same specimen area, surface structure and morphology of the microstructure are characterized in great detail by the relief and orientation contrast in secondary and backscatter electron images, element distributions are accessed by energy dispersive spectroscopy (EDS), wavelength dispersive spectroscopy (WDS), or cathodoluminescence analysis, and the orientations of single grains and phases can now be determined, as a complement, by EBSD.

Robert A. Schwarzer, David P. Field, Brent L. Adams, Mukul Kumar, Adam J. Schwartz

Chapter 2. Dynamical Simulation of Electron Backscatter Diffraction Patterns

To extract the maximum amount of information from experimental electron backscatter diffraction (EBSD) patterns, it is necessary to realistically model the physical processes that lead to the formation of the characteristic diffraction features in the form of Kikuchi bands and lines. Whereas the purely geometrical relations in the observed networks of bands and lines can be explained by mapping out Bragg’s law for the relevant reflecting lattice planes, the dynamical theory of electron diffraction is needed to explain the observed intensities. This theory takes into account the fact that electrons interact strongly with matter, which leads to multiple elastic and inelastic scattering of the electron waves in a crystal.

Aimo Winkelmann

Chapter 3. Representations of Texture

The field of materials science and engineering is fundamentally concerned with manipulating the microstructure of materials in order to control their properties. Electron backscatter diffraction (EBSD) dramatically enhances our abilities in this regard, by providing extensive crystallographic orientation information of a given two-dimensional section of a microstructure. As this technique has been developed and combined with chemical analysis and serial sectioning methods, it has become possible to access complete three-dimensional chemistry, phase, and crystal orientation information; in short, the microstructural state of a polycrystal may now be completely quantified.

Jeremy K. Mason, Christopher A. Schuh

Chapter 4. Energy Filtering in EBSD

Alwyn Eades, Andrew Deal, Abhishek Bhattacharyya, Tejpal Hooghan

Chapter 5. Spherical Kikuchi Maps and Other Rarities

Spheres, or more accurately, spherical surfaces, are important for electron backscatter diffraction (EBSD). Electron backscatter patterns (EBSPs) and pole figure and misorientation axis data are ideally suited to display on the surface of a sphere.

Austin P. Day

Chapter 6. Application of Electron Backscatter Diffraction to Phase Identification

The distribution, morphology, and stability of material phases govern the bulk properties of virtually all of the technologically relevant materials used to design engineering components and products. Phase identification and characterization are therefore critical to the development and use of practical materials. In this chapter, we will focus on the application of electron backscatter diffraction (EBSD) to phase identification.

Bassem El-Dasher, Andrew Deal

Chapter 7. Phase Identification Through Symmetry Determination in EBSD Patterns

David J. Dingley, S.I. Wright

Chapter 8. Three-Dimensional Orientation Microscopy by Serial Sectioning and EBSD-Based Orientation Mapping in a FIB-SEM

Conventional EBSD-based orientation microscopy is a 2-dimensional (2D) characterization method, which is applied to plane cuts through a sample. Statistical stereological techniques can be used to gain insight into the 3D aspects of microstructure, as in, e.g., Adams (1986), Adams et al.

Stefan Zaefferer, Stuart I. Wright

Chapter 9. Collection, Processing, and Analysis of Three-Dimensional EBSD Data Sets

Three-dimensional (3D) characterization methods are required to completely determine microstructural descriptors such as the true shape and size of features, the number of features, and the connectivity between these features. Experimental methods to characterize microstructure in 3D have undergone dramatic improvements in the past decade, and there now exists a host of methodologies that are capable of determining 3D microstructural information, ranging from counting individual atoms to imaging macro-scale volumes. The state of the art for this field has been reviewed recently in a Viewpoint Set for Scripta Materialia (Spanos 2006).

Michael A. Groeber, David J. Rowenhorst, Michael D. Uchic

Chapter 10. 3D Reconstruction of Digital Microstructures

The main motivation for this chapter is a decidedly practical one, in that many questions can be asked about the effect of microstructure on materials’ response. Often, the use of simple average quantities such as “grain size” is inadequate; instead one may need to consider the possibility that the full three-dimensional (3D) microstructure is important. Calculations by hand being self-evidently impracticable, computers must be used, and thus a digital microstructure is required in which all relevant microstructural features are fully described. We find sufficient complexity in materials with predominantly single-phase grain structures, perhaps containing dispersions of second phase particles. Other chapters, however, describe more complex microstructures based on, e.g., titanium alloys.

Stephen D. Sintay, Michael A. Groeber, Anthony D. Rollett

Chapter 11. Direct 3D Simulation of Plastic Flow from EBSD Data

Given high quality EBSD scans of microstructures, researchers naturally wish to assess the properties and performance of the material. For virtually all aspects of material behavior, this involves a model for the material’s response, and considerable uncertainty in the predictions arises from uncertainties in both model form and model parameters. Classical crystal viscoplasticity is often used to assess the plastic flow behavior of polycrystalline materials (Kocks et al. 1998); but more sophisticated approaches are under active development. For example, Arsenlis et al. (2004) have included the effects of detailed dislocation density evolution, including dislocation flux terms that capture heterogeneity in the flow; and Acharya and Beaudoin (2000) have examined interactions between lattice curvature and hardening.

Nathan R. Barton, Joel V. Bernier, Ricardo A. Lebensohn, Anthony D. Rollett

Chapter 12. First-Order Microstructure Sensitive Design Based on Volume Fractions and Elementary Bounds

Prior chapters of this book have focused largely on the experimental aspects of EBSD technique. We shift our attention here to a mathematical framework for establishing invertible linkages between the mesoscale internal structure of the material and the macroscale properties exhibited by the material. It is noted that the current practice in engineering design does not pay adequate attention to the internal structure of the material as a continuous design variable. The design effort is often focused on the optimization of the geometric parameters of the component being designed using robust macroscale numerical simulation tools, while the material selection is typically relegated to a relatively small database. Furthermore, material properties are usually assumed to be isotropic, and this significantly reduces the design space.

Surya R. Kalidindi, David T. Fullwood, Brent L. Adams

Chapter 13. Second-Order Microstructure Sensitive Design Using 2-Point Spatial Correlations

In this chapter we are concerned with second-order interrelations between structure, properties, and processes of materials. Structure can be described in many different ways. The most common metrics of structure involve “first-order” (volume fraction) information: for example, the orientation distribution function. Such metrics serve well as the basis for property relations that do not depend significantly upon the geometrical placement of the material constituents. However, many properties (such as those relating to failure) depend critically upon the geometrical distribution of particular material components, and hence benefit enormously from knowledge of the “higher order” structure.

David T. Fullwood, Surya R. Kalidindi, Brent L. Adams

Chapter 14. Combinatorial Materials Science and EBSD: A High Throughput Experimentation Tool

The impact of EBSD in combinatorial experimentation lies in its value as a nondestructive focused probe for high throughput screening of materials libraries via backscattered diffraction. The types of information gathered by EBSD are of course well documented (especially in the present and the previous companion volume [Schwartz et al. 2000]).

Krishna Rajan

Chapter 15. Grain Boundary Networks

Statistical information about grain orientations within a polycrystal has been available to materials researchers for many decades. In particular, the orientation distribution, or crystallographic texture information, has been measured using X-ray diffraction techniques since about 1950. Consequently, the role of texture in materials performance and design is widely appreciated and commonly taught in the core Materials Science curriculum. However, texture data represent only “one-point” statistics, and do not capture microstructural geometry or topology.

Bryan W. Reed, Christopher A. Schuh

Chapter 16. Measurement of the Five-Parameter Grain Boundary Distribution from Planar Sections

Although EBSD is essentially a surface measurement technique, strategies have been developed to extend its capabilities to the characterisation of microstructure in three dimensions. These developments have been realised because advances in both EBSD technology and computing power have rendered the collection of large data sets a routine matter. There are several scientific motivations for characterizing the three-dimensional structure of polycrystals by EBSD. In this chapter, we describe the application of EBSD to the measurement of internal interface planes by application of both serial sectioning and also a stereological technique known as the “five-parameter analysis.”

Gregory S. Rohrer, Valerie Randle

Chapter 17. Strain Mapping Using Electron Backscatter Diffraction

In this chapter we review the progress that has been made toward elastic strain (i.e., stress) mapping using electron backscatter diffraction. In particular we focus on development of an analysis method based on using cross-correlation to determine small shifts in the EBSD patterns with respect to a reference pattern. The pattern shifts are determined at many subregions dispersed across the wide angular span of the EBSD pattern, and the magnitude and angular distribution of shifts allows the strain and rotation tensor to be determined. Pattern shifts at a resolution of ±0.05 pixels, or in some cases even better, have been reported, which corresponds to a sensitivity of ∼±10^–4 in the components of the strain and rotation tensor.

Angus J. Wilkinson, David J. Dingley, Graham Meaden

Chapter 18. Mapping and Assessing Plastic Deformation Using EBSD

This chapter reviews approaches for mapping and assessing plastic deformation using EBSD. This discussion will be focused on the approaches based upon EBSD pattern rotation. Pattern rotation can be mapped or quantified in terms of straight orientation change, local misorientation, average misorientation, or the calculation of geometrically necessary dislocation densities. In polycrystals, the misorientation can be mapped using several different kinds of metrics to visualize plastic deformation around cracks, indentations, and inside deformed grains. We will discuss a number of average misorientation metrics that have been developed to quantify the correlation between plastic deformation and EBSD data. Finally, we will survey the more recent work in the measurement and display of geometrically necessary dislocations and their connection to deformation structures in metals.

Luke N. Brewer, David P. Field, Colin C. Merriman

Chapter 19. Analysis of Deformation Structures in FCC Materials Using EBSD and TEM Techniques

In a large number of industrially important metals and alloys, a fraction of the dislocations generated during deformation remain trapped and arranged into well-defined dislocation boundaries (Bay et al. 1992; Hansen and Juul Jensen 1999; Hughes and Hansen 2000; Li et al. 2004). Extensive investigations using the transmission electron microscope have established that these dislocation boundaries separate volumes of different crystal orientations, and that two classes of dislocation boundaries can be defined (Liu et al. 1998; Hansen 2001).

Oleg V. Mishin, Andrew Godfrey, Dorte Juul Jensen

Chapter 20. Application of EBSD Methods to Severe Plastic Deformation (SPD) and Related Processing Methods

Refinement and homogenization of microstructure are highly beneficial to the mechanical properties of engineering materials. Conventional thermomechanical treatments for this purpose typically include deformation processing to von Mises equivalent strains ≤5, while recently developed severe plastic deformation (SPD) processing methods have enabled systematic investigation of equivalent strains >10. Ultrafine grain sizes (even in the nanometer range) and strain hardening may contribute to dramatic improvements in ambient strength. Also, strength-toughness relationships as well as resistance to cyclic loading may be improved when grain refinement is combined with other strengthening mechanisms, although interactions among strengthening, toughening, crack initiation, and crack growth mechanisms are complex and often alloy-specific.

Terry R. McNelley, Alexandre P. Zhilyaev, Srinivasan Swaminathan, Jianqing Su, E. Sarath Menon

Chapter 21. Applications of EBSD to Microstructural Control in Friction Stir Welding/Processing

Sergey Mironov, Yutaka S. Sato, Hiroyuki Kokawa

Chapter 22. Characterization of Shear Localization and Shock Damage with EBSD

This chapter provides examples of the application of EBSD characterization to microstructures influenced by two conditions: (1) shear localization, and (2) dynamic deformation and damage from shock loading.

John F. Bingert, Veronica Livescu, Ellen K. Cerreta

Chapter 23. Texture Separation for α/β Titanium Alloys

Over the past few decades, titanium and titanium alloys have been utilized in numerous applications due to their low density, high strength, and excellent corrosion resistance. With the highest strength to density ratio and a high melting temperature (1670°C), titanium alloys are always selected over other competing metallic materials, such as high strength aluminum alloys, for many high temperature aerospace applications (e.g., turbine engines).

Ayman A. Salem

Chapter 24. A Review of In Situ EBSD Studies

In the first fully automated electron backscatter diffraction (EBSD) system (Wright and Adams 1992), later termed orientation imaging microscopy (OIM) (Adams et al. 1993), four seconds were required to index each EBSD pattern. A few in situ studies were performed using these early systems involving a tensile stage (Weiland et al. 1996) and a heating stage (Humphreys and Ferry 1996). While this was a big step forward, modern commercial systems are capable of speeds over three orders of magnitude faster. Fortunately, while automated EBSD technology was advancing, scanning electron microscope (SEM) technology was also advancing.

Stuart I. Wright, Matthew M. Nowell

Chapter 25. Electron Backscatter Diffraction in Low Vacuum Conditions

Most current scanning electron microscopes (SEMs) have the ability to analyze samples in a low vacuum mode, whereby a partial pressure of water vapor is introduced into the SEM chamber, allowing the characterization of nonconductive samples without any special preparation. Although the presence of water vapor in the chamber degrades electron backscatter diffraction (EBSD) patterns, the potential of this setup for EBSD characterization of nonconductive samples is immense. In this chapter we discuss the requirements, advantages, and limitations of low vacuum EBSD (LV-EBSD), and explain how this technique can be applied to a two-phase ceramic composite, as well as hydrated biominerals, as specific examples of when LV-EBSD can be invaluable.

Bassem S. El-Dasher, Sharon G. Torres

Chapter 26. EBSD in the Earth Sciences: Applications, Common Practice, and Challenges

In the Earth’s middle and lower crust and mantle, rocks deform by creep, and it has long been recognized that lattice preferred orientations (LPO) of the mineral constituents in deformed rocks yield useful information on creep deformation mechanisms, conditions, and kinematics (Leiss et al. 2000; Turner and Weiss 1963; Wenk and Christie 1991). Bulk LPO data are traditionally measured by X-ray texture goniometry, and more recently using neutron and synchrotron sources (Leiss et al. 2000).

David J. Prior, Elisabetta Mariani, John Wheeler

Chapter 27. Orientation Imaging Microscopy in Research on High Temperature Oxidation

High temperature oxidation of steel has been studied for reducing steel losses and for understanding descaling of oxides (Kuiry et al. 1994; Tomellini and Mazzarano 1988; Sachs and Tuck 1968). Surface defects, such as scale pits and residues, are frequently observed on steel surfaces after hot rolling. The occurrence of surface defects is related to the formation of oxide scale. These defects are undesirable for the surface quality control of slab in the hot rolling process. The quality control of steel products is highly dependent on the removal of scale on slab during the hot rolling process. This is directly related to the scale structure formed in high temperature oxidation.

Bae-Kyun Kim, Jerzy A. Szpunar

Backmatter