© 2005 The Royal Microscopical Society Journal of Microscopy, Vol. 219, Pt 3 September 2005, pp. 115– 121 Received 20 March 2005; accepted 9 June 2005 Blackwell Publishing, Ltd. Electron backscattered diffraction characterization technique for analysis of a Ti 2 AlNb intermetallic alloy G. L. WYNICK & C. J. BOEHLERT* Alfred University, School of Engineering, Alfred, NY 14802, U.S.A. *Michigan State University, Department of Chemical Engineering and Materials Science, East Lansing, MI 48824-1226, U.S.A. Key words. Electron backscatter diffraction, microstructure, titanium alloy. Summary This investigation was conducted to ascertain the benefits of electropolishing after mechanical polishing for electron backscattered diffraction of a Ti 2 AlNb intermetallic Ti-21Al- 29Nb (at.%) alloy containing the orthorhombic (O) and body-centered-cubic (BCC) phases. Electropolishing was per- formed at - 40 °C in 6% H 2 SO 4 methanol solution. Atomic force microscopy was used to measure the surface topography in attempt to correlate nano-scale surface roughness with electron backscatter diffraction pattern quality. The results suggest that mechanically polishing with colloidal silica (SiO 2 ) or alumina followed by electropolishing is a sufficient surface preparatory technique for producing quality electron back- scattered diffraction patterns for O + BCC microstructures. However, poor pattern quality results after mechanically polishing without electropolishing. High-quality orientation maps for O-dominated O + BCC microstructures were only possible through mechanical polishing followed by electro- polishing. The data also suggest that surface roughness, on the order of 50 nm, has less effect on pattern quality than sub- surface deformation. Overall, removing the near-surface damage was more critical than reduction of topography. Received 20 March 2005; accepted 9 June 2005 1. Introduction Electron backscatter diffraction (EBSD) is a surface-sensitive materials characterization technique as the depth below the specimen surface from where the backscattered electrons are generated is shallow (nanometres to a few micrometres depending on sample and beam conditions) due to the limited mean free path of the elastically scattered electrons (Prior et al., 1999). A relatively flat and distortion-free sample sur- face is necessary in order to acquire quality electron back- scattered diffraction Kikuchi patterns (EBSPs) so that automated computer evaluation is reliable. Generation of useful EBSPs depends upon the critical physical relationship between the electron beam, sample and detector within the SEM. This relationship can be upset with an increase in surface rough- ness of the sample; it has been suggested that roughness on the order of the grain size is unacceptable (Katrakova & Mucklich, 2001). For this reason, flat surfaces are desired when preparing specimens for EBSD. However, preparation methods that produce plane surfaces are known to cause varying degrees of subsurface damage, and preparation methods that minimize damage do not necessarily result in plane surfaces (Petzow, 1999). Metals are particularly susceptible to damage in the form of microstrain when mechanical polishing meth- ods are used. This can be mitigated to some extent by careful selection of abrasives and adjustment of polishing parameters. One thing that becomes evident when preparing samples for EBSD is that techniques that give exceptional results in reveal- ing a metal’s microstructure for optical microscopy will often not produce acceptable EBSPs. For instance, alumina (Al 2 O 3 ; 0.05 μm average particle size) and colloidal silica (SiO 2 ; 0.06 μm average particle size) are frequently regarded as standard abrasives for fine polishing to mirror-quality sur- faces yet EBSPs are not always obtained after such final polish- ing. This is due to the remaining residual distortion at the surface, mainly deformation in the case of metals. The scratch depth after each polishing step is on the order of the particle size while the deformation layer is often much thicker (Lihl & Mayer, 1960; Petzow, 1999). Therefore, an additional step is sometimes required, especially for soft metals as well as those that readily form surface oxides. For the latter metals, including plutonium and cerium, low-energy vacuum ion-sputtering is beneficial (Boehlert et al., 2001, 2003a,b). A method that has proven to be successful in producing surfaces with low microstrain is electropolishing. However, pro- longed electropolishing tends to increase surface roughness. Mechanical polishing with a sufficiently low resulting micro- strain followed by reasonably short electropolishing times has proven to be an ideal way to generate surfaces suitable Correspondence to: Dr Carl Boehlert. Fax: +1 517 432 1105; e-mail: boehlert @egr.msu.edu