EBSD for Crystal Particle Analysis

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The analysis of a material’s crystallographic properties can provide a researcher with a wealth of information, including the identification, processing history, and much more. Although many techniques can be used to obtain various pieces of information, electron backscatter diffraction (EBSD) can give a more complete picture of not only what the substance is, but what has happened to it (melting, extreme pressure, etc).

EBSD is a SEM-based electron diffraction technique that allows for direct observation of the crystallographic properties of a material. This technique is effective when testing relatively deformation-free crystalline samples, with a grain or crystal size of approximately 100nm in bulk, or 10nm as particulate. Bulk material must be polished before analysis, and particulate must be an amorphous substrate or an electron transparent substrate.

Microtextural Characterization

Used for phase identification (when used with energy dispersive x-ray spectroscopy, or EDS) and crystal orientation analysis, EBSD is a powerful tool for microtextural characterization, which includes:

  • strain measurement
  • misorientation distribution
  • grain boundary properties
  • grain size measurements
  • lattice preferred orientation
  • phase identification and mapping

 

In practice, EBSD mapping can indicate crystal orientation in a colored map for easier identification and ready interpretation. Figure 1 shows a forescattered image that indicates qualitative differences in orientation to determine structurally unique regions in the sample. This imaging is unique in the sensitivity to crystal orientation and spatial resolution. The data that is produced from a mapping experiment can be processed in displayed in any number of ways to show spatial, phase, and crystallographic information. Also, data can be presented using sophisticated mathematical representations such as pole figures or orientation distribution functions (Figure 2).

Figure 1 – Forescattered electron image (top left), EBSD grain map (top right), inverse pole figure EBSD map (bottom left) and average misorientation EBSD map (bottom right) from steel sample.

 

Figure 2 – pole figure produced from EBSD data in Figure 1 showing distribution of various crystal planes with respect to the sample surface.

 

Phase Identification Technology Comparison Case Study

Scientists and engineers commonly perform analysis on asbestos particles. Using transmission electron microscopy (TEM), the images returned can be ambiguous and don’t provide enough information to give a positive phase ID (Figure 3). Typically, TEM diffraction patterns contain information only from two intersecting crystallographic planes (selected area electron diffraction patterns). This can lead to the situation where more information is necessary to make a positive phase identification.

Figure 3 typical data used for phase identification from a TEM. Top left: electron micrograph, bottom left: EDS spectra, top and bottom right: selected area electron diffraction patterns.

 

Comparison of Existing Materials

However, using SEM/EBSD analysis, the same particle produced an EBSD pattern with enough information to determine the particle was olivine rather than asbestos (Figure 4). Because EBSD patterns contain information from many crystallographic planes, it allows for comparison to databases of existing materials, and rapid assessment of useful crystallographic properties. In spite of EBSD being employed mainly on polished bulk samples, RJ Lee Group scientists have found ways to implement the technique on particulate samples without the need for polishing.

The result of the comparison is that in some instances, EBSD can provide a clear phase identification where TEM was unable to provide information suitable for a clear identification. The ability to perform this testing on particulate samples is a non-traditional application of the EBSD technique and has many industrial applications.

Figure 4 SEM/EBSD result. Left: secondary electron micrograph. Top right: EBSD pattern. Bottom right: EBSD pattern with olivine indexing solution overlaid.

 

In summary, EBSD is an advanced tool for the study of a wide variety of crystalline materials. Data gathered by EBSD provides insight to materials that allow for phase identification and quantitative metallography. Using EBSD for materials research and development, quality assurance, and failure investigations can provide insights unavailable from other techniques. RJ Lee Group is continuing to provide the highest level of scanning electron microscopy and microanalysis by the addition of this powerful tool.

For more information on EBSD, please contact Bryan Bandli of RJ Lee Group at 1.800.860.1775 or by clicking the button below.


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