Automated crystal lattice orientation mapping using a computer-controlled SEM

Abstract

A backscatter Kikuchi diffraction attachment to an SEM enables the convenient investigation of individual grain orientations on bulk surfaces. Their relation to microstructural features gives insight into many aspects of anisotropic materials properties. The formation of backscatter Kikuchi patterns and the experimental set-up for their acquisition are briefly outlined. The interactive and automated indexing of patterns and the fully Automated Crystal lattice Orientation Mapping (ACOM) with a computer-controlled SEM are presented in detail. Digital beam scan requires, as a consequence of the high tilt of the specimen with respect to the beam, current calculation of pattern centre and diffraction length (autocalibration) and dynamic focusing by the software. The automated measurement of lattice orientations takes less than half a second per image point on a Pentium Pro 200 MHz PC. Crystal lattice orientation maps (COM) are constructed by assigning to each grid point in the image a colour specific for the grain orientation, the misorientation or the grain boundary character. For a quantitative representation of the spatial distribution of microscale texture, an orientation-to-colour key is used by colour shading inverse pole figures, sections through Euler space or sections through Rodrigues orientation space. Texture components of interest can be highlighted by distinct colours in order to reveal textural inhomogeneities. Typical applications are given.