Application of Crystal Orientation Mapping to Intra-Grain Misorientations

Extract

Crystal orientation mapping (COM), which is also referred to as orientation imaging microscopy (OIM), is a powerful tool which opens up enormous possibilities for investigation of materials. The principle of COM is that the microstructure is displayed or mapped according to the orientation of sampled volumes of crystal. These data are obtained in the scanning electron microscope by moving either the electron beam or the specimen stage through predetermined steps and collecting an electron back-scatter diffraction (EBSD) pattern. Typically, a null orientation is represented by a black pixel and colours are used to depict orientations, thus allowing discrete orientation changes such as grain boundaries to be plotted directly in a map format. This is exemplified in figure 1 which shows an orientation map generated from pure aluminium which has undergone 5% cold rolling. The diffiiseness of EBSD patterns further permits strain changes to be mapped.