FORMATION AND PRECIPITATION MECHANISM OF NANOSCALE AL PARTICLES IN AL-NI BASE AMORPHOUS-ALLOYS

Nanoscale fcc-Al particles which are homogeneously dispersed within am orphous phase have been obtained by annealing the amorphous alloys. Sc anning and isothermal calorimetry, together with X-ray diffraction and high resolution transmission electron microscopy (TEM) have been empl oyed to study precipitation of nanoscale Al particles in Al-based amor phous alloys. In the cases of Al87Ni10Ce3, Al87Ni10Zr3 and Al87Ni7Cu3C e3 alloys, the monotonously decreasing isothermal calorimetric signal, characteristic of a grain growth process has been observed in the cou rse of precipitation of nanoscale Al particles in these amorphous allo ys. It is shown that the Al particles grow by diffusion controlled gro wth with a small activation energy in the range of 1.3-1.7 eV. TEM of as-quenched Al87Ni10Ce3 revealed an amorphous structure but a signific ant concentration fluctuation was observed in the alloy by small-angle X-ray scattering (SAXS). The concentration fluctuation is presumed to be associated with pre-existing nuclei. Formation of nanocrystalline fcc-Al through a grain growth process has been identified in several A l-based amorphous alloys with lambda in the range of 0.04-0.07 (lambda , is a parameter responsible for the strain of the matrix induced by s olute elements) and with Al content in the range of 82-90 at.%. This s tudy gave indications in structure-control for gaining a nanoscaie fcc -Al dispersed in an amorphous matrix. (C) 1997 Acta Metallurgica Inc.