Automated determination of crystal orientations from electron backscattering patterns

Niels Christian Krieger Lassen

Summary The electron backscattering pattern (EBSP) technique is widely accepted as being an extremely powerful tool for measuring the crystallographic orientation of individual crystallites in polycrystalline materials. Procedures which allow crystal orientations to be calculated on the bases of the position of the bands or the zone axes of EBSPs have existed for several years now. Until recently, however, the localization of either the bands or the zone axes of EBSPs has required the valuable time and attention of a human operator, thus obviously limiting the amounts of orientation data that can be collected by this method.

This thesis describes the development and implementation of a system which enables crystallographic orientations to be obtained fully automatically through the use of computerized analysis and interpretation of EBSPs. More specifically, this thesis will describe the design of a pattern recognition procedure which enables 8 to 12 bands to be localized in typical EBSPs from a modern system. It will be described, how these automatically localized bands can be indexed and used for optimal estimation of the unknown crystal orientations.

A necessary prerequisite for precise determination of crystallographic orientations from EBSPs is accurate knowledge of three calibration parameters which describe the position of the point from which the patterns are emitted relative to the phosphor screen on which they are recorded. This thesis will describe a novel method by which these calibration parameters can be estimated with high precision.

The quality of EBSPs provides important information about the reliability of the measured crystal orientations and about the perfection of the lattice in which the pattern is generated. A measure which allows the quality of EBSPs to be evaluated quantitatively is therefore described.

Presently, little is known about the uncertainty of the lattice orientations which can be measuted from EBSPs. This subject will be discussed in detail in this thesis. With the application of newly developed statistical methods for analyzing orientation data it will be shown how the relative precision of lattice orientations measured from EBSPs can be described. By applying this methodology to a large number of EBSPs of varying quality it is demonstrated that the precision of automatically measured crystal orientations is comparable to the precision obtained, when the positions of four to five bands are supplied by an experienced and careful operator.

IMM Ph.D Thesis 3, 1994

Last modified August 18, 1996
Finn Kuno Christensen