PHASE-TRANSFORMATIONS AND STRUCTURE CHARACTERISTICS OF THE AL65CU17.5CO17.5 DECAGONAL PHASE

The phase transformations and structure characteristics of the Al65Cu17.5Co17.5 alloy were studied by neutron diffraction. The scheme of Yamamoto and Ishihara can satisfactorily index the diffraction patterns. The Al-Cu-Co decagonal phase is stable in the temperature range between 973 and 1350 K. At the low temperature end it relaxes to a microcrystalline approximant structure. At the high temperature end, it melts directly into liquid. The scheme of Yamamoto and Ishihara can perfectly index the neutron powder diffraction patterns (a = 7.212 angstrom, c = 4.184 angstrom at 973 K). We propose that it is the average quasiperiodic sublattice that determines the powder diffraction characteristics of the microcrystalline structure at room temperature which can also be indexed in decagonal phase notation.