The Study On Magnetic Properties And Crystallized Behavior For The Fe-(Nd,Co,Zr)-Y-B Bulk Amorphous Alloys

Amorphous alloys have a lot of excellent properties, such as high strength, high hardness, corrosion resistance and wear resistance. In recent years, the research of bulk amorphous alloys has become one of the hotest areas in the materials science. Fe-based bulk amorphous alloys also have been drawing increasing attention in recent years due to good magnetic properties. At the same time Fe is the most common metal in nature, with abundant resources and low cost. It is regretted that the Fe-based bulk amorphous alloys with good magnetic properties are difficult to be prepared; particularly ferromagnetic bulk amorphous alloys could be found only in a few systems. It greatly limits its application. Moreover, the study of the Fe-based ferromagnetic bulk amorphous alloys was more in soft magnetic properties but less in hard magnetic properties, especially less in the crystalline behavior and magnetic changes. The purpose of this paper is to prepare a new Fe-based bulk amorphous alloy with larger size, and investigate the magnetic properties, crystalline behavior of amorphous alloys and the change of magnetic properties after crystallization.Through adjusting the composition of the Fe-Nd-Y-Zr-B alloys systems, a new Fe₆₈Nd₅Zr₂Y₄B₂₁ bulk amorphous alloy with larger glass-forming ability was prepared by suction casting into the copper mold at 0.8mm in sheet thickness, 10mm in width, and 50mm in length. The as-cast Fe₆₈Nd₅Zr₂Y₄B₂₁ bulk amorphous alloy exhibited good soft magnetic properties.The structure, magnetic properties and crystalline behavior for the as-cast and anneal at different temperatures of Fe-(Nd,Co,Zr)-Y-B alloys were investigated by X-ray diffraction (XRD), differential thermal analysis (DTA), vibrating sample magnetometer (VSM) and thermo-gravimetric analysis (TGA).Firstly the influence by adding various alloys and changing different contents of Co Zr Nd on the glass-forming ability and magnetic properties of Fe-(Nd,Co,Zr) -Y-B alloys were investigated. The results suggested that the additions of Co had a little effect to GFA, 2at% addition of Zr and 5at% addition of Nd can probably improve GFA of the Fe-(Nd,Co,Zr)-Y-B alloys systems. With Nd contents increasing, the GFA droped dramatically and the alloy crystallized. When Co was added, the saturation magnetization had a little change and the coercive force decreased sharply. But the saturation magnetization and coercive force had a little change with the Cocontent increasing. When Zr was added, the alloy with 2at% of Zr addition exhibited the soft magnetic behavior. But the coercive force of the Fe-Nd-Zr-Y-B alloys became larger with Zr conent keeping on increasing. When Nd was added, the alloys exhibited the soft magnetic behavior with Nd addition less than 5at%. But the coercive force of the Fe-Nd-Zr-Y-B alloys became larger significantly with Nd content increasing.The crystalline behavior of Fe_73-xNd_xZr₂Y₄B₂₁(x = 0,2,5,7) bulk amorphous alloys was investigated. The results showed that the crystalline behavior was different with Nd adding or not. The crystalline temperature of the alloy with Nd addition was higher 50K than without Nd addition. By comparing the crystallization of different conents of Nd, the results found that the magnetic properties and crystalline behavior were different. The alloy without Nd addition was still exhibited soft magnetic properties after crystallization. The alloy with 2at% of Nd addition had a little coercive force after crystallization, but the change of coercive force was slightly. It increased from 0kA/m to 33kA/m only. It was noticed that the as-cast bulk amorphous alloy with 5at% of Nd addition exhibited the soft magnetic behavior, but the alloy tured to exhibite the hard magnetic behavior after crystallization. The coercive force of the bulk amorphous alloy with 5at% of Nd addition had obviously changed from 0kA/m to 143kA/m after crystallization. The phase of crystallization were changed from amorphous phase to α-Fe phase, Fe₃B phase, Nd₂Fe₁₄B phase, NdFe₄B₄ phase, and B₃Fe₃Nd phase. The appearance of hard magnetic behavior was due to the soft magnetic phase of α-Fe phase and Fe₃B phase and hard magnetic phase of Nd₂Fe₁₄B phase which produced strong exchange magnetic coupling in nanometer scales. It provided a new way to fabricate new bulk nanocomposite permanent material by crystallization. At the same time, it was found that the coercive force of Fe₆₈Nd₅Zr₂Y₄B₂₁ bulk amorphous alloy was increased limitedly after crystallization because of appearing the crystalline phases of NdFe₄B₄ phase and B₃Fe₃Nd phase. The alloy with 7at% of Nd addition exhibited the hard magnetic behavior as cast. It was noticed that the coercive force of the alloy was still increased from 109kA/m to 167kA/m after crystallization. The hard magnetic properties was enhanced. The results suggested that the crystalline phases had little change after crystallization, but the the proportion of the crystalline phases was found to be changed. The non-magnetic phase of NdFe₄B₄ phase and B₃Fe₃Nd phase were reduced, while the hard magnetic phase of Nd₂Fe₁₄B phase was increased, which is the reason why the coercive force was still increased after crystallization. It provided a way to improve the hard magnetic properties of the alloy with the crystalline phases by optimum annealing. But it is tobe studied in future how to enhance and improve the hard magnetic properties of the alloy after crystallization through reducing the non-magnetic phase and increasing the hard magnetic phase by optimizing annealed processes and adjusting proper composition.