Effect Of High Magnetic Field On Crystallization Behavior Of Rare Earth Based And Fe-based Amorphous Alloys

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 several rare earth based and Fe-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 Nd55Al15Co20amorphous alloy has been performed using a continuous DSC technique. The results showed that each characteristic temperature of metallic glass had apparent kinetics effects. In the heating rates region (5-80K/min) which was used in experiments, the Kissinger equation, Lasocka equation, Augis-Bennet equation, Ozawa equation and VFT equation were used to fit the characteristic temperatures of metallic glass. We found that all the five equations could well describe the relationship between the characteristic temperature and the heating rate of the metallic glass when the heating rate is ranging from5to80K/min. The apparent activation energy value in the glass transition and crystallization process of the amorphous alloy which was calculated from the Kissinger equation was less than the result that calculated by Augis-Bennet equation and Ozawa equation. The continuous heating phase transition diagram of the Nd55Al25Co2o amorphous alloy was constructed using the fitted VFT equations.The relationship between the crystallized volume fraction and apparent crystallization activation energy for the the Nd55Al25Co2o amorphous alloy was obtained using Doyle-Ozawa method. The results showed that the crystallization activation energy has no much change with the increasing crystallization volume fration. The crystallization mechanism curves of the Nd55Al25Co2o amorphous alloy have been obtained and analyzed using the Johnson-Mehl-Avrami equation and Normal Grain Growth equation.The effect of high magnetic field on the crystallization of Nd55Al25Co20and Gd55Al25Co20amorphous alloys was investigated by XRD, isothermal DSC analysis technical and TEM in this paper. The results indicated that the high magnetic field enhanced the precipitation of fcc-Nd in the Nd55Al25Co2o amorphous alloy, reduced the crystallization activation energy and increased the nucleation process. For the Gd55Al25Co20alloy, the high magnetic field enhanced the precipitation of fcc-Gd.Finally, the effect of steady high magnetic field and gradient high magnetic field on the crystallization and magnetic properties of (Fe0.36Co0.36B0.192Si0.048Nb0.04)100-xCux(x=0,0.5,1) amorphous alloys was investigated by XRD and VSM. The results suggested that the high magnetic field had little effect on crystallization of (Fe0.36Co0.36B0.192Si0.048Nbo04)99.5Cu0.5and (Feo.36Co0.36B0.192Si10.048Nbo.o4)99Cu amorphous alloys. When the amorphous ribbons are parallel to the direction of the high magnetic field, the steady high magnetic field enhanced the precipitation of a-(Fe,Co,Si) in (200) of the Fe36Co36B192Si4.8Nb4amorphous alloy,but inhibited the precipitation of α-(Fe,Co,Si) in (200) of the Fe36Co36B19.2Si4.8Nb4amorphous alloy, when the amorphous ribbons are vertical to the direction of the high magnetic field. Steady magnetic field had little effect on Fe36Co36B19.2Si4.8Nb4amorphous alloy magnetic properties in aspects of its coercivity and magnetic saturation intensity. Gradient high magnetic field inhibited the precipitation of a-(Fe,Co,Si) in (200) of the Fe36Co36B19.2Si4.8Nb4amorphous alloy, and had also little effect on the magnetic properties of the alloy.