EBSD Explained
Techniques
Applications
Hints and Tips
Technology
OXFORD INSTRUMENTS EBSD PRODUCTS
CMOS Detector RangeAZtecHKL Acquisition SoftwareAZtecCrystal Processing Software
The basic information provided by electron backscatter diffraction (EBSD) is relatively simple:
From these 2 primary pieces of information, the technique can provide many additional microstructural measurements, as will be shown below.
The performance of the technique is dependent on a multitude of factors, including the sample preparation, the scanning electron microscope, the electron beam parameters, the EBSD detector and software and, finally, the sample itself. However, the following table provides an indication of the data quality and performance of the EBSD technique:
Parameter |
Performance |
Effective Spatial Resolution |
25-200 nm (Bulk EBSD) 2-20 nm (Transmission Kikuchi Diffraction) |
Angular Precision |
0.1-0.5° (Hough based indexing) 0.001-0.01° (High precision techniques) |
Angular Accuracy |
~2° |
Analysis Speed |
Up to ~4500 measurements per second |
Most EBSD analyses are fully automated, with phase and orientation data being collected rapidly from a regular grid of points on the sample surface. These data are then used to reconstruct the microstructure in the form of phase or orientation maps and, from these, further information is extracted. There are many ways in which EBSD data can be presented, and this is discussed in more detail in the Techniques section, on the Displaying EBSD Data page.
The tabs below give some more details about the types of information that EBSD can provide, with subsequent pages giving examples of specific applications and links to downloadable application notes.
EBSD is commonly used to map the distribution and measure the area fraction of phases in a sample. Phase discrimination may be solely based on crystallographic differences, or may incorporate chemical information (from energy dispersive X-ray spectrometry, EDS). The typical output would be a phase map, along with the respective area % of the individual phases, as shown in the example on the right from a deformed igneous rock.
EBSD can also be combined with EDS to help identify unknown phases (such as precipitates) in samples. This “phase-ID” approach is extremely rapid (e.g. typically taking 10 – 60s), but requires a suitable phase database and, as such, is not true phase identification. More information can be found on the “Integration with EDS” page.
EBSD Phase map of a deformed oxide gabbro rock sample
Crystal orientation data is the fundamental output of the EBSD technique and, as such, the technique is ideal for the measurement of textures (also known as lattice or crystallographic preferred orientation). EBSD is fast and also provides information that is spatially resolved, so that we can determine how the texture varies across a sample, giving the technique an advantage over some other texture-analysis methods such as X-ray or neutron diffraction. However, EBSD will only provide texture measurements on the surface of samples, unless used in conjunction with serial sectioning approaches.
Texture measurements are typical for a range of sample types, notably in the metals processing industries and in the geosciences (where the crystallographic preferred orientation is used to infer the activation of specific slip systems). The image on the right shows the texture of a-Ti in an additively manufactured Ti64 alloy, using pole figures.
{0001} and {10-10} pole figures showing the texture in an additively manufactured Ti64 alloy, with the preferred alignment of the poles to {0001} parallel to the build direction (Z).
Orientation mapping using EBSD provides spatially resolved information about crystallographic orientations, from which rigorous grain size and shape information can be derived. This includes:
All of these can be plotted in map form, as shown in the image on the right, or used for rigorous statistical analyses.
Grain analyses based on EBSD data are used in all applications, ranging from quality control of processed metals and alloys to the grain structure in nano-scale surface coatings. The latest EBSD software packages can also reconstruct the grain structure of high temperature phases following displacive phase transformations (such as prior austenite grains in martensitic steels) – read about Parent Grain Reconstruction in the Technology section.
Map showing the aspect ratio of the best fit ellipses for austenite grains in a weld zone of a duplex stainless steel.
Detailed crystallographic information about boundaries within samples can be derived from the EBSD orientation measurements. This gives the EBSD technique an advantage over other techniques since it provides full information about the nature of the boundaries as well as excellent statistics. Information about boundaries derived from EBSD maps include:
As an example, the following images are taken from a deformed and heat-treated Al-Mg alloy. The inverse pole figure shows the rotation axes for low angle boundaries (between 2° and 5°), with a clear clustering about the <111> axis. The map highlights in red the boundaries >2° disorientation that have their rotation axis within 5° of the <111> direction. This combination of crystallographic and spatial information highlights the fact that this particular type of low angle boundary preferentially forms in the lowermost grains in this area, presumably controlled by the original orientation.
Inverse pole figure showing the low angle boundary rotation axes
Pattern quality map with a boundary overlay. Black – high angle boundaries, Blue – low angle boundaries (2-10°), Red – boundaries (>2°) with a rotation axis within 5° of the <111> direction.
A lot of EBSD analyses are performed in order to characterise and to quantify the strain in samples. Although it is possible to measure elastic strain using high angular resolution (HR) EBSD analyses, EBSD is more commonly used to characterise plastic strain. This can be achieved in a number of ways:
The study of deformation and strain using EBSD is common in many different application fields, but is particularly powerful for the study of failure and crack propagation. As an example, the map on the right highlights the plastic deformation at the tip of an array of cracks in a duplex steel sample.
Kernel average misorientation map highlighting local strain at crack tips in a duplex steel sample.
© Oxford Instruments 2024