Transition de phases réversible icosaédrique - rhomboédrique de l'alliage Al63,5Fe12,5Cu24

Abstract

A reversible phase transformation between icosahedral and rhombohedral structures has been studied by transmission electron microscopy. Some transient states have been characterised by x-ray diffraction using a 4 circles goniometer on a synchrotron beam line. The microcrystalline rhombohedral phase is stable at low temperature; above 675 o C it transforms into an icosahedral phase via an intermediate pentagonal structure. The icosahedral phase, metastable at low temperature, transforms between 500 and 675 o C into the rhombohedral phase via different transient states: modulated icosahedral phases and pentagonal approximants. These intermediate states have been interpreted as resulting of shear waves of phason type, propagating along the basis vectors of a 6-D hyper cubic lattice and polarized along the perpendicular space. The chemical composition variations associated to these shear waves and predicted by the theory have been experimentally observed