APPROXIMANT AND FRANK-KASPER PHASES

It is shown by electron microscopy that planar defects in Frank-Kasper (or tetrahedrally close-packed (TCP)) phases have a very particular o rganization. In the three cases analysed in this paper, the icosahedra l axes appear to be a useful reference in order to depict the microstr ucture. Our analysis reveals a hierarchical isocahedral organization i n TCP phases. Since this approach is based on cell identification comp ared with the icosahedron, Frank-Kasper phases are considered as quasi crystal approximants. The microstructural information, orientation rel ationships and defect organization emphasize the significance of such a description.