© 2004 The Royal Microscopical Society Journal of Microscopy, Vol. 213, Pt 3 March 2004, pp. 296–305 Received 24 June 2003; accepted 10 November 2003 Blackwell Publishing, Ltd. Phase differentiation via combined EBSD and XEDS M. M. NOWELL & S. I. WRIGHT EDAX/TSL 392 East 12300 South, Draper, Utah 84020, U.S.A. Key words. Electron backscatter diffraction, orientation imaging microscopy, phase differentiation, X-ray energy-dispersive spectroscopy. Summary Electron backscatter diffraction (EBSD) and orientation imaging microscopy have become established techniques for analysing the crystallographic microstructure of single and multiphase materials. In certain instances, however, it can be difficult and/or time intensive to differentiate phases within a material by crystallography alone. Traditionally a list of candi- date phases is specified prior to data collection. The crystallo- graphic information extracted from the diffraction patterns is then compared with the crystallographic information from these candidate phases, and a best-fit match is determined. Problems may arise when two phases have similar crystal structures. The phase differentiation process can be improved by collecting chemical information through X-ray energy- dispersive spectroscopy (XEDS) simultaneously with the crystallographic information through EBSD and then using the chemical information to pre-filter the crystallographic phase candidates. This technique improves both the overall speed of the data collection and the accuracy of the final characterization. Examples of this process and the limitations involved will be presented and discussed. Received 24 June 2003; accepted 10 November 2003 Introduction Automated electron backscatter diffraction (EBSD) or orienta- tion imaging microscopy (OIM) is a proven technique for making spatially specific measurements of crystallographic orientation in polycrystalline materials. This automated technique allows the measurements to be made on samples over prescribed areas. The measurements are made at individual locations on a regular array defined by the user. At each point, an EBSD pattern is collected, the position of the bands in the pattern are located using image processing routines and the orientation determined from the geometry of the bands. This procedure is performed without any operator intervention. In multiphase materials it is also possible to differentiate the phase at each point in an OIM scan. This is done for an individual point in the scan by performing the indexing process for each of the constituent phases and finding the phase with the best solution to the detected bands in the diffraction pattern. The solutions for each of the phases are ranked according to a user-defined weighting of indexing votes, confidence index, angular fit and band-width ratios, and the phase with the highest ranking factor assigned to the measurement point (see Appendix). The term ‘differentiate’ indicates EBSD is being used to automatically select the phase from a set of known phases present in the material. Phase differentiation is a process used during automated scans. By contrast, for EBSD applications the term ‘phase identifi- cation’ indicates generally the use of EBSD to assist a user in identifying unknown phases in a material. ‘Phase identifica- tion’ is an interactive process occurring at manually selected points in the microstructure. EBSD is used to assist in the selection of a phase from a list of candidate phases derived from a comprehensive database. The list of candidate phases is generally derived from the database by filtering based on chemical composition (Goehner et al., 1992; Michael & Goehner, 1993). Phase identification is often performed prior to running a multiphase OIM scan in order to identify the constituent phases to be differentiated during the scan. Phase differentiation works well when the crystal struc- tures of the phase candidates are relatively dissimilar. Even when two phases have the same point group symmetry they can be distinguished if the diffracting planes are different. For example, a body-centred cubic phase is relatively easily differ- entiated from a face-centred cubic phase owing to the unique- ness of the interplanar angles between the diffracting planes for each phase. A good application of EBSD phase differentiation is on samples where the constituent phases have essentially the same chemical composition but vary in crystallographic structure. In these cases, the constituent phases cannot be distinguished by standard X-ray energy-dispersive spectroscopy (XEDS) maps. For example, consider the andalusite, kyanite and sillimanite polymorphs of Al 2 SiO 5 . These polymorphs have essentially the same composition, and therefore cannot be distinguished by XEDS, but they have different crystal structures, which can be distinguished using EBSD. EBSD also performs well in cases where the chemical com- position may vary; yet, the varying elements have overlapping Correspondence: M. M. Nowell. E-mail: matt.nowell@ametek.com