The Crystallization Behavior Of The Fe-Nd-Al-B-M(M=Dy, Zr) Amorphous Alloys

The preparation of the Nd-Fe-Al bulk amorphous alloys, having a highcoercivity at room temperature, successfully opened up a new field for theapplication of the amorphous alloy due to the simple fabrication process andgood formability. Based on our previous work, this study mainly focuses on theeffect of the elements Dy and Zr on the crystallization behavior of theamorphous Fe-Nd-Al-B alloys. In this dissertation, vibrating samplemagnetometer (VSM), differential scanning calorimeter (DSC), X-raydiffraction (XRD), scanning electron microscope (SEM), focused ion beam (FIB)and high resolution transmission electron microscopy (HRTEM) are employedto study the magnetic properties, phase composition and microstructure of theFe-Nd-Al-B-(Dy, Zr) alloys. The reason for the significant change in themagnetic properties during the crystallization process is discussed, and theresults are summarized as follows:1. The Fe-Nd-Al-B-Dy bulk amorphous alloys prepared by copper-moldcasting method all show hard magnetic properties at room temperature. Themagnetic property of the (Fe0.51Nd0.35Al0.10B0.04)98.8Dy1.2alloy with thediameter of5mm achieves the maximum value. The coercivity up to533.2kA/m and the remanence up to21.1Am2/kg are obtained. It is consist of theamorphous phase, Nd(Dy)2Fe14B, Nd2Fe17, Nd and Nd3Al phase.2. The rod-shaped Fe-Nd-Al-B-Dy bulk alloys are consist of theinhomogeneous microstructure. The value of the coercivity is higher in theedge, while the saturation magnetization is lower. The inhomogeneousmicrostructure also exists in the rod-shaped alloy with the minimumdiameter of2mm.3. For the1mm sheet of the (Fe0.51Nd0.35Al0.10B0.04)100-xDyx(x=0～3at.%)alloys, the glass-forming ability and the thermal stability can be improved bythe minor addition of Dy(x=1.2). For x=0, the annealed alloys still behavehard magnetic properties under different annealing conditions. Thecoercivity can increase by90%at low temperature (713K), which is due tothe increasing volume fraction of the hard magnetic Nd2Fe14B phase. Forx=1.2and3, the change of the magnetic property during the crystallizationshows the same discipline. The saturation magnetization, remanence andcoercivity gradually decrease with the increase of annealing temperature.The amount of the hard magnetic Nd(Dy)2Fe14B phase is gradually reduced.The hard magnetic phase, together with the amorphous phase, is finallytransformed into the non-magnetic phases, which are harmful to themagnetic property.4. The enhancements of the glass-forming ability and the thermal stability are observed in the Fe-Nd-Al-B bulk alloy with the small Zr addition. For the1mm sheet, the magnetic properties of the (Fe0.51Nd0.35Al0.10B0.04)100-xZrx(x=2,4) alloys are weakened with the increasing temperature, and they finallybecome soft magnetic properties. The areas of the hysteresis loops areobvious in the as-cast samples and the samples annealed at low temperature(713K), which are caused by the amorphous phase. For the alloys annealedat high temperature (above753K), the areas of the hysteresis loops aredisappeared. The annealed alloys are consist of the Fe-rich phase andNd-rich phase eutectic morphology, and the completely crystallized alloysare composed of Nd, Nd2Fe17, Fe2Zr and some unknown phases.