Crystallization of icosahedral phase from glassy Pd-U-Si alloys.

Abstract

The glassy-to-icosahedral phase transformation in Pd-U-Si alloys is studied by using x-ray and transmission electron diffraction. It is found that the transformation is polymorphous and it proceeds via a nucleation and growth process. The nucleation is homogeneous, and a large number of nuclei (\ensuremath{\simeq}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$) are found in the early stage of transformation which can be explained by the existence of short-range icosahedral order in the corresponding glassy phase. It appears that the icosahedral particles grow by atomic attachment at the particle interphase boundary. Some particles are in pentagonal or hexagonal shape, which reflects the internal symmetry of icosahedral phase. Coarsening is believed to occur during the growth process. A picture of the transformation is presented and comparisons are made with other results on glassy-to-icosahedral phase transformations.