Orientation imaging microscopy: Bridging the grain-boundary structure-properties linkage in polycrystalline materials

Recent developments in computer-automated microdiffraction technique enable rapid sampling of the field of local lattice orientation in polycrystalline materials. From such data images of the microstructure have been constructed which differ from conventional micrographs in that contrast is directly linked to measured gradients in lattice orientation. This new form of microscopy is now called Orientation Imaging Microscopy (OIM). OIM provides an opportunity to measure, with statistical relevancy, the local details of the crystallographic and geometrical structure of the grain-boundary network. From such data it should be possible to construct a map linking local structure and certain physico-chemical properties of grain boundaries over the entire range of their natural occurrence in polycrystals. In this paper an experimental and computational approach to this comprehensive mapping is described for the thermodynamic properties of grain boundaries. Also described is the relationship between OIM data and the dislocation density tensor, which may prove useful in quantifying extrinsic driving forces for grain boundary motion.