| Metallic glass has attracted wide interest due to its special physical, chemical and mechanical properties. The study on crystallization mechanism is very important in developing non-equilibrum nucleation theory and practical applications. Meanwhile, it has been demonstrated that high magnetic field has remarkable influence on the crystallization process of metallic glasses. Therefore, the aim of the work was to investigate the crystallization kinetics and the effect of high magnetic field on amorphous alloys of Zr60Cu20Ni10Al10bulk metallic glass (BMG) and several RE-based amorphous alloys by isothermal annealing under high magnetic field, differential scanning calorimeter (DSC), X-ray diffractometer (XRD), transmission electron microscopy (TEM) and the analysis methods of DSC.Crystallization kinetics of Zr60Cu20Ni10Al10BMG has been performed using a continuous DSC technique. The results showed that the crystallization behavior of Zr60Cu20Ni10Al10BMG is closely related to the heating rate. The crystallization process at sslow heating rates region (1-20K/min) differs from that at rapid heating rates region(30-80K/min). When the Kissinger equation, Ozawa equation, Augis&Bennet equation and Lasocka equation were used to describe the relationship between the characteristic temperatures of the BMG and the heating rate, the data should be divided into two groups, i.e. sslow heating rates region and rapid heating rates region. However, a single VFT equation could well illustrate the relationship between the charactertic temperatures and the heating rates. The activation energy of the Zr60Cu20Ni10Al10BMG at slow heating rates is much higher than that at rapid heating rates. The crystallization mode of the Zr60Cu20Ni10Al10BMG at slow heating rates is mainly based on nucleation. However, its crystallization process at rapid heating rates is controlled by nucleation and growth with an obvious change of the growth rate at the advanced stage of the crystallization. The continuous DSC technique and TEM were used to inveatigate the effect of the high magnetic field on the crystallization process of the Zr60Cu20Ni10Al10BMG It has been found that the local crystallization activation energy of the Zr60Cu20Ni10Al10alloy annealed under high magnetic field is much smaller than that of the alloys annealed without high magnetic field, suggesting the alloys annealled under higher magnetic field have smaller local crystallization activation energy. The magnetic field enhanced the nucleation during the iso-thermal crystallization process of Zr60Cu20Ni10Al10BMG, and restrained the growth of the nuclei.The continuous DSC technique was also used to study the crystallization of the several Gd-based amorphous alloys. The results showed that the increasing of the Gd in the alloys reduced the thermal stability of Gd-based amorphous alloys. Adding Zr in Gd-based amorphous alloys had little effect on the thermal stability. The Kissinger and VFT equations could well describe the relationship between the characteristic temperatures and the heating rate of Gd-based amorphous alloys. The Gd-based amorphous alloy with more addition of Gd element had larger crystallization activation energy, while the addition of the Zr element in Gd-based alloys had little effect on the crystallization activation energy. The Gd-based amorphous alloy with high Gd content had reduced nucleation rate, and growth of nuclei was dominate crystallizaiotn mode. Zr increased the nucleation of the Gd-based amorphous alloys, but had little effect on the growth of the alloys.The effect of high magnetic field on the crystallization of RE55AI25Co20(RE=Gd, La) amorphous alloys was investigated by XRD, isothermal DSC analysis technical and TEM in this paper. The results indicated that magnetic field enhanced the precipitation of fcc-Gd in the Gd55Al25Co20amorphous alloy. In the La55Al25Co20alloys, magnetic field reduced the active energy and increased the nucleation. |
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