The simultaneous acquisition of chemical data (through EDS) and crystallographic data (through EBSD) in the SEM is commonplace. A new method is described which makes use of this simultaneous data acquisition to discriminate crystallographically-similar materials in real time.
EBSD is a powerful analytical technique capable of a wide variety of microstructural analyses, including the ability to discriminate between phases based on crystallography. However, limitations exist, and there are cases where indexing by conventional inter-band angle matching alone, fails to discriminate phases yielding very similar Kikuchi patterns, for example, in the case of many fcc metals with close unit cell dimensions.
A number of different solutions have been applied to solve this, both in real-time and post-acquisition. In one real-time method, Kikuchi band width matching is used to successfully exploit inter-planar spacing differences between phases. Utilising high accuracy band detection methods, reliable comparisons between measured and calculated bandwidths for candidate phases are used to determine a best match. This method is useful to a band width difference of approx.10% or more.
Another real-time alternative is phase differentiation on the basis of chemistry, in which no minimum difference in crystal structure or unit cell parameter is necessary. This technique uses EDS data acquired simultaneously with the EBSD data for each point analysed. When more than one viable solution results from indexing alone, EDS information for the point is used to weight the results in favour of the solution whose chemical spectrum best matches a reference spectrum for the phases involved.
This technique will be illustrated with a number of examples, from both geological and materials applications.