THE PHASE-DIAGRAM AND STRUCTURES OF THE TERNARY ALCUFE SYSTEM IN THE VICINITY OF THE ICOSAHEDRAL REGION

The phase diagram of the ternary system (Al, Cu, Fe) has been systematically studied around the icosahedral region. At 680-degrees-C, the i-region extends approximately over a triangle with vertices of Al, Cu and Fe composition of respectively 62.4-24.4-13.2, 65-23-12 and 61 28.4-10.6. This region splits schematically into 3 fields: (i) the perfect icosahedral phase which is stable down to the lowest possible annealing temperature where atomic diffusion is active in a tiny region of composition close to Al62.3Cu24.9Fe12.8; (ii) a well defined periodic phase with rhombohedral lattice which transforms reversibly into ico near 710-degrees-C in the lower part of the triangle; (iii) a complex region characterized by additional diffraction effects (peak broadening, lineshapes. etc.) which may correspond to various approximant structures closely related to the i-phase.