Anomalous change in nanocrystallization of amorphous Zr-Cu-Ni alloy

Abstract

Employing X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM), an anomalous change in the nanocrystallization of metallic Zr70Cu20Ni10 glass under two different conditions, i.e., continuous heating and isothermal annealing, has been observed. Both TEM observations and XRD results confirm that the first exothermic reaction in the continuous heating DSC traces of metallic Zr70Cu20Ni10 glass mainly corresponds to the precipitation of the Zr2Cu phase, while the second one mainly corresponds to the precipitation of the Zr2Ni nanoparticles. In contrast to this, when annealed in the supercooled liquid region the preferential precipitation phase of metallic Zr70Cu20Ni10 glass mainly corresponds of the Zr2Ni nanocrystals instead of the Zr2Cu phase. The origin of such an anomalous change can be explained by the Kirkendall effect between Cu and Ni atoms for the former and the difference in heat of mixing between Zr-Ni and Zr-Cu atomic pairs. Crystallization of amorphous alloys has been extensively studied because of practical and theoretical interest in crystal nucleation and growth in a high undercooling regime [1]. Two methods are often utilized to investigate the crystallization process of amorphous alloys, i.e. the continuous heating and isothermal annealing processes. For the continuous heating process, we can obtain the apparent activation energy for crystallization of an amorphous alloy by means of