Recent developments in EBSD have delivered improvements in indexing reliability and accuracy [1]. However, some individual phases continue to pose indexing challenges, especially those that present extremely similar Kikuchi patterns to the EBSD detector for different crystallographic orientations, so that the indexing engine may not clearly discern the correct orientation solution. This phenomenon is called “pseudosymmetry”, as it commonly involves relatively high intensity bands in certain patterns with an apparent higher symmetry than the crystal structure actually possesses. In many cases, only very slight differences in inter-band angle separate candidate solutions, and only robust and accurate band detection may identify the correct one among them.
Conventional Hough-based band detection methods used in commercial EBSD systems are sufficiently accurate for the great majority of indexing requirements. High accuracy Hough transform settings do improve band detection accuracy and are useful in mitigating pseudosymmetric misindexing [2], however these result in greater image transform time and reduced data acquisition speeds and even then may not completely eliminate pseudosymmetry problems in the most chronic cases.
New band detection refinement methods promise to improve indexing performance further for some of the most important cases; and at reasonable speeds. These methods deliver higher accuracy band detection by iteratively comparing the positions of simulated bands with bands in the actual Kikuchi pattern image, using expected versus actual band widths and importantly, accounting for the hyperbolic shape of bands on the phosphor screen.
In addition to delivering high precision crystallographic orientation data and improved phase discrimination, this method is sufficiently sensitive to resolve fine differences in inter-band angle to nearly eliminate many cases of pseudosymmetric misindexing. For especially difficult cases, for example gamma TiAl alloys, known single-phase pseudo-symmetric orientation relationships may be specifically examined by the system to help further resolve these indexing issues.