Problems in determining the misorientation axes, for small angular misorientations, using electron backscatter diffraction in the SEM

The errors associated with calculating misorientation axes from electron backscatter diffraction (EBSD) data have been assessed experimentally. EBSD measurements were made on the same grains after imposed rotations of 2 degrees, 5 degrees, 7 degrees, 10 degrees, 12 degrees, 17 degrees, 27 degrees and 180 degrees around the normal to the specimen surface. The misorientation magnitudes and the misorientation axes associated with the imposed rotations have been calculated from the EBSD data. Individual measurements of misorientation axes are precise for misorientation magnitudes greater than approximately 20 degrees. The errors must be appreciated when assessing misorientation data at lower misorientation magnitudes and particularly at magnitudes less than 5 degrees. Where misorientation axes can be characterized by the distribution of axes from a number of individual measurements, current EBSD techniques are satisfactory, for data sets of 30 measurements, as long as misorientation magnitudes are 10 degrees or more. With larger data sets it may be possible to extend this approach to smaller misorientation magnitudes. For characterization of individual misorientations less than 5 degrees, new EBSD techniques need to be developed.