Research On Crystallization And Magnetic Properties Of RE-Fe-B Based Nanocomposite Magnet

Nanocomposite permanent magnetic materials with high remanence and maximum energy product, and low rare earth content have great potential in many fields of applications. Compared to Nd-Fe-B based permanent magnetic alloys, Pr-Fe-B based alloys have received relatively less attention. However, Pr-based nanocomposite may have higher coercivity and maximum energy product than its Nd-based counterpart since the hard magnetic phase of Pr2Fe14B has larger value of magnetic anisotropy field than Nd2Fe14B phase. Hence, in this paper the crystallization and hard magnetic properties of two types of PrFeB-based nanocomposites, i.e. Pr2Fe14B/Fe3B and Pr2Fe14B/α-Fe, are systematically investigated. Pr2Fe14B/Fe3B and Pr2Fe14B/α-Fe nanocomposite alloys were prepared by melt spinning and heat-treatment. The structure and properties and the effects of the composition and crystallization parameters on the performance of these alloys have been studied by the methods of XRD, DSC and VSM.In Pr2Fe14B/Fe3B alloy series, the study on crystallization behavior shows that the heating rate can effectively change the crystallization of amorphous materials. The faster the heating rate, the higher is the temperature of crystallization. The addition of high melting point transition element Ta significantly increases the activation energy of the Fe3B phase during crystallization, which leads to an increased crystallization temperature and improved the stability of amorphous phase. The addition of Nb can not only increases the crystallization activation energy of the Fe3B phase but also inhibits the formation of metastable Pr2Fe23B3 phase during the alloy crystallization process. The study on the magnetic properties shows that the addition of Ta element increases the coercivity. Partial substitution of Pr by Dy can also increase the coercivity but decrease the remanence of the alloy. Co is found to substitute Fe in both hard magnetic phase and soft magnetic phase. Co substituted alloys have fine and uniform grain size, which improves the exchange coupling between the hard and soft phases. Therefore, improved combination of magnetic properties has been obtained. Addition of Nb to Pr2Fe14B/Fe3B series can improve the magnetic properties for the crystallization time of 5 minutes, probably because Nb can inhibit the formation of metastable Pr2Fe23B3 phase. Based on the optimized composition and process excellent combined properties of Br=1.2T, Hcj=242.1kA/m and (BH)max=84.7kJ/m3 have been successfully obtained in the Pr4.5(Fe0.9Co0.1)77B18.5 alloy.In Pr2Fe14B/α-Fe alloy series, Ta and Co additions also improve the magnetic properties. However, the addition of Nb was found not beneficial to the properties, possibly due to the formation of non-magnetic Nb-rich phase. In this low rare earth Pr2Fe14B/α-Fe alloy series, good properties of Br=1.4T, Hcj=313.86kA/m and (BH)max=65.02kJ/m3 were obtained in Pr8Fe87B4Ta1 alloy.