Characterization of bicrystals using kikuchi patterns

Abstract

Three parameters, the misorientation angle, misorientation axis, and boundary normal, have been used to describe a general bicrystal,e.g., two adjacent grains, subgrains, or twins. An analysis developed to determine these parameters is presented. The angle and axis of misorientation are calculated from a misorientation matrix obtained from two Kikuchi patterns, one taken from each of the two crystals. To obtain the boundary normal, a specimen tilt is made inside the electron microscope. A rotation matrix specifying the actual specimen tilt is formulated from two Kikuchi patterns taken from the same crystal before and after tilt. With this rotation matrix and the change of projected boundary images before and after tilt, the boundary normal can be calculated. It is demonstrated that 1) for high-angle bicrystals, the misorientation angle may be determined to within ±0.2 deg, and the misorientation axis to within 0.1 deg; 2) for low-angle bicrystals, the misfit angle can be obtained to within ±0.1 deg, and the misfit axis to within 4 deg; and 3) the boundary normals so determined are generally accurate to 2 deg if suitable correction is made for the magnification change resulting from the specimen tilt.