CHANGEMENTS DE PHASES ET MICROSTRUCTURES
J. Phys. IV France 04 (1994) C3-169-C3-174
Transition de phases réversible icosaédrique - rhomboédrique de l'alliage Al63,5Fe12,5Cu24N. MENGUY, M. AUDIER, P. GUYOT and M. DE BOISSIEU
Laboratoire de Thermodynamique et Physico-Chimie Metallurgiques, UA 29 du CNRS, ENSEEG, BP. 75, 38402 Saint Martin d'Hères, France
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°C it transforms into an icosahedral phase via an intermediate pentagonal structure. The icosahedral phase, metastable at low temperature, transforms between 500 and 675°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.
© EDP Sciences 1994