The basic information provided by electron backscatter diffraction (EBSD) is relatively simple:
Phase identification and confirmation of the 3D orientation of the lattice at each analysis point EBSD technology is based on these two main pieces of information and can additionally provide many additional microstructure measurements, as shown below. The performance of EBSD technology depends on a variety of factors, including: sample preparation, scanning electron microscopy, electron beam parameters, EBSD detectors and software, and the sample itself. Nonetheless, the table below gives a general indication of the data and performance of EBSD technology:
Most EBSD analyses are fully automated, with phase and orientation data that can be quickly collected from a raster area of points on the sample surface. This data is then used to reconstruct the microstructure in the form of a phase distribution map or orientation distribution map, and further information can be extracted from this data.
Appearance. EBSD is often used to plot the distribution of phases in a sample and to measure the area fraction of the phases. Distinguish between different phases, which can be based solely on crystallographic differences, or may contain chemical information (from energy dispersive spectrometers, EDS). A typical output is a facies distribution map, with the percentage of area corresponding to each phase, as shown in the deformed igneous rock example below. EBSD can also be used in conjunction with EDS to help identify unknown phases (e.g., precipitates) in a sample. This "phase identification" method is very fast, but requires a suitable phase database, so it is not true phase identification in itself.
Texture. Crystal orientation data is the most basic output of EBSD technology, and as such, it is an ideal technique for measuring texture (also known as crystal preferred orientation). EBSD is fast and provides spatially resolved information so that we can determine how the texture changes in the sample, which gives EBSD an advantage over other texture analysis methods such as XRD or neutron diffraction. However, EBSD can only provide texture measurements of the sample surface unless combined with in situ sectioning methods. Texture measurements are a typical analytical method for a range of sample types, especially in the metalworking industry and in the geological sciences where crystal preferential orientation (CPO) is used to infer the initiation of a particular slip system). The following example shows the -Ti texture in an additively manufactured Ti64 alloy represented by a pole diagram.
Grain. EBSD orientation mapping provides spatially resolved information about the crystallographic orientation, from which strict grain size and shape can be derived. This information includes:
Grain size, grain shape, topography, grain average orientation, grain internal orientation variation, twin ratio, all of this information can be plotted as a map of the map below, as shown in the figure below, or for rigorous statistical analysis. Grain analysis based on EBSD data has a wide range of applications: from quality control in metal and alloy processing to grain structure for nanoscale surface coatings. The latest EBSD post-processing software is able to reconstruct the grain structure of the high-temperature phase before the displacement phase transition (e.g., the original austenite grain in martensitic steel).
Grain boundaries. From the orientation measurements of the EBSD, detailed crystallographic information about the grain boundaries of the sample can also be derived. This gives EBSD an edge over other techniques as it provides complete information and perfect statistics about the nature of grain boundaries. Information about grain boundaries derived from EBSD map includes:
Grain Boundary Orientation Difference InformationGrain Boundary Rotation AxisGrain Boundary Traces (Full Orientation of Grain Interfaces Can Be Measured Using 3D-EBSD)Special Grain Boundary Identification (e.g., Twinned or Coincident Locations, Lattice Grain Boundaries (CSL))Complete Grain Boundary Length StatisticsThe following example images are from Al-MG alloys after deformation and heat treatment. The inverse pole plot shows the axis of rotation of the low-angle grain boundary (2° 5°), with a clear segregation on the <111> axis. Grain boundaries with a misorientation difference greater than 2° and a rotation axis within 5° of the > of the <111 are marked in red. This combination of crystallography and spatial information highlights the fact that this particular small-angle grain boundary, preferentially formed in the lowest grain of the field of view, may be controlled by the initial orientation.
Strain. Many EBSD analyses are performed to characterize and quantify strain in a sample. Although elastic strain can be measured by high-resolution EBSD (HR-EBSD) analysis, EBSD is more commonly used to characterize plastic strain. This can be achieved in a number of ways:
Local lattice orientation gradients (e.g., KAM measurements) Geometrically Necessary Dislocations (GNDs) Densities, Intragranular Orientation Deviations, Intragranular Orientation Scattering, Small-Angle Grain Boundary Distributions, Studying deformation and strain with EBSD is common in many different applications, but is particularly useful for studying failure and crack propagation. As an example, the image below illustrates the plastic deformation of the crack tip in a duplex steel sample.