EBSD provides information from the sample surface. However, there is often a requirement to get the same type of information from a 3D volume, in order to study grain structures, grain size and interface boundaries. Depending on the size of the volume of interest, this can be achieved in several ways: For large scale features it is possible to use mechanical sectioning techniques to expose a new surface at different depths of the sample, and to analyse at these different depths.  For small scale features, it is not practical to take the sample out of the SEM chamber and then reposition it to collect more data. A solution is to use an SEM combined with a focused ion beam (FIB-SEM), where the ion column is used to mill away the surface between each EBSD map.

This process is typically automated. To achieve this the sample must be placed in a geometry suitable for both milling, with the ion beam parallel to the sample surface and for EBSD data collection (Figure 1).  Depending on the setup it can involve moving the sample automatically between these two working geometries to have an optimum geometry for both, on other setups it is done without moving the sample and having one geometry which allows milling as well as EBSD data acquisition.

By repeating the process of acquiring an EBSD dataset and exposing a new surface, it is possible to generate a 3D representation of the microstructure within the analysed volume. To get good data resolution, it can be necessary to collect data from many tens of slices (potentially more than a hundred).

An example from a Cu dataset collected with a step size of 0.2 mm in the x, y and z directions is shown in Figure 2. Here, this technique is used to present and study interfaces between grains as well as provide information about the grain size and shape. 

Figure 1 Schematic showing an example of the EBSD geometry for a FIB-SEM used for 3D-EBSD analysis.

Figure 2 Example shows 3D EBSD analysis through a Cu sample;
A) Reconstructed and processed 3D orientation map;
B) Cross-sections in X, Y and Z planes;
C) A single grain selected and highlighted.