Microstructure evolution upon devitrification and crystallization kinetics of Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 melt-spun glassy ribbon

The crystallization behavior of glassy Zr57Ti8Nb2.5Cu13.9Ni11.1Al7.5 produced by melt spinning was investigated by differential scanning calorimetry, x-ray diffraction, electron microscopy, and atom probe investigations. The devitrification of the as-spun ribbon occurs by primary crystallization of a metastable nanoscale quasicrystalline phase during the first stage of the crystallization process, followed by successive transformation into intermetallic compounds at higher temperatures. The kinetics investigation reveals that quasicrystal formation is characterized by two overlapping processes: the first step probably linked with the redistribution of one or more elements, most likely Al and Zr, between the quasicrystalline phase and the remaining amorphous matrix, and the second step corresponding to the crystallization itself. Furthermore, a higher value of the activation energy for quasicrystal formation compared to other quasicrystal-forming alloys suggests an increased complexity of the crystallization mechanism. (C) 2004 American Institute of Physics.