Magnetic Properties and Microstructure of Directly Quenched R-Fe-Ti-Zr-Cr-B-C Bulk Magnets ( ${\hbox {R}}={\hbox {Nd}}$ , Pr, and Mischmetals)

Magnetic properties of directly quenched R_9.5Fe_72.5-yTi_2.5Zr_0.5Cr_yB_{15 -x}C_x (R=Nd, Pr, and mischmetals (MM); x=0-0.5; y=0-1) bulk magnets with a diameter of 0.9-1.1 mm and a length of 15 mm have been studied. Thermal magnetic analyses show that large amount of 2:14:1 phase together with a slight α-Fe phase are found for most of the developed magnets. Besides, a slight substitution of C for B and Cr for Fe in Nd_9.5Fe_72.5Ti_2.5Zr_0.5B₁₅ magnets can effectively refine the grain size of the bulk magnet, resulting in the remarkable enhancement of the magnetic properties. The optimal magnetic properties of Br = 5.9 kG, _iH_c=8.2 kOe and (BH)_max=7.2 MGOe could be attained in Nd_9.5Fe_71.5Ti_2.5Zr_0.5Cr₁B_14.5C_0.5. In addition, for R_9.5Fe_71.5Ti_2.5Zr_0.5Cr₁B_14.5C_0.5 magnets, even though the magnets with R=MM exhibit slightly lower B_r and (BH)_max than the magnet with R=Nd, magnetic properties of B_r=5.6-5.7 kG, _iH_c=10.3 -11.4 kOe, and (BH)_max=6.0-6.9 MGOe can also be achieved for the magnets with R = MM(A) and MM(B).