PERFECTION AND GROWTH OF ICOSAHEDRAL QUASICRYSTALS STUDIED BY SYNCHROTRON X-RAY IMAGING

摘要

Knowing if defects are generated in the quasicrystal grains during their growth is very important to better understand the long range propagation of quasicrystalline order as well as quasicrystal stability. We have carried out the first in situ and real time observation of the quasicrystal growth which has clearly disclosed both, the shape of the growing interface and its defective state. Therefore we have studied the solidification of an AlPdMn alloy giving quasicrystal grains, by synchrotron X-ray imaging, combining thereby the radiography and X-ray topography techniques. Radiography allowed us to clearly evidence a facetted growth proceeding by lateral motion of ledges at the solid-melt interface and controlled by the interface kinetics rather than by the local heat flow as widely thought. Thus a realistic estimate of the kinetic coefficient was deduced from the solid-melt interface undercooling which indicates that the quasicrystal growth is more likely comparable to both semiconductor and oxide growths than to pure metal growth. The X-ray topographs recorded simultaneously with radiographs, revealed that a lot of strains and defects are generated in the quasicrystal grains during their growth.