Mechanisms driving primary crystallization of Al 87Ni 7Cu 3Nd 3 amorphous alloy

Abstract

Al 87Ni 7Cu 3Nd 3 ribbons, prepared by melt-spinning, have been analysed by differential scanning calorimetry, and their nanostructural evolution has been studied by combining heat treatments with conventional X-ray diffraction, high-temperature X-ray diffraction, high resolution transmission electron microscopy and selected area electron diffraction. The results show that the melt-spun samples have an overall amorphous structure, though they contain quenched-in crystalline embryos. Nanocrystallization starts with the stabilization of some of the pre-existing embryos, showing parabolic growth in the first stages. Soft impingement very soon becomes the controlling mechanism, and the particle density of fcc-Al stabilizes at ∼10 17 cm −3. No clear end of nanocrystallization is observed, since secondary crystallization of intermetallic phases is promoted by continuous heating above 583 K. In this paper a new method is proposed to treat calorimetric data in the framework of the isokinetic approach. It is shown that the nanocrystallization process follows an isokinetic behaviour, with an apparent activation energy of 105 kJ/mol.