Abstract
Nanoscale fcc-Al particles which are homogeneously dispersed within amorphous phase have been obtained by annealing the amorphous alloys. Scanning and isothermal calorimetry, together with X-ray diffraction and high resolution transmission electron microscopy (TEM) have been employed to study precipitation of nanoscale Al particles in Al-based amorphous alloys. In the cases of Al 87Ni 10Ce 3, Al 87Ni 10Zr 3 and Al 87Ni 7Cu 3Ce 3 alloys, the monotonously decreasing isothermal calorimetric signal, characteristic of a grain growth process has been observed in the course of precipitation of nanoscale Al particles in these amorphous alloys. It is shown that the Al particles grow by diffusion controlled growth with a small activation energy in the range of 1.3–1.7 eV. TEM of as-quenched Al 87Ni 10Ce 3 revealed an amorphous structure but a significant 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 Al-based amorphous alloys with λ in the range of 0.04–0.07 (λ is a parameter responsible for the strain of the matrix induced by solute elements) and with Al content in the range of 82–90 at.%. This study gave indications in structure-control for gaining a nanoscale fcc-Al dispersed in an amorphous matrix.
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