A Study on the Phase Evolution and Magnetic Properties of Nd $_{9.5 - 1.5{\rm x}}$ Fe $_{{\rm bal}.}$

Phase evolution, microstructure, and magnetic properties of Nd_9.5-1.5xFe_bal.Ti_2.5Zr_0.5B_15+2x (x = 0-4) rod magnets with a diameter of 0.9 mm have been investigated. For the as-cast magnets, large amount of 2:14:1 phase exists for x = 0, while an additional amorphous phase appears for x = 1-2, yet large amount of orthorhombic Fe₃ B (o-Fe₃B) phase is easily formed together with slight 2:14:1 and amorphous phases for x = 3-4. The appearance of amorphous phase with x = 1-2 results in the reduction of permanent magnetic properties drastically, which implies that annealing is necessary to improve the hard magnetic properties of these rod magnets. After annealing the magnets with x = 1-2, the amorphous phase is crystallized into 2:14:1 and Fe₃B phases, as a result, the magnetic properties were improved from B_r = 4.7-5.2 kG,_i H_c = 2.7-10.9 kOe, and (BH)_max = 1.1-3.7 MGOe for the as-cast magnets to B_r = 5.7-6.8 kG,_i H_c =6.2-7.4 kOe, and (BH)_max = 5.5-5.6 MGOe. For the magnets with x = 3 and 4, annealing treatment is not necessary due to the existence of large amount of orthorhombic Fe₃ B (o-Fe₃B) in the as-cast state, consequently, exhibit extremely low permanent magnetic properties.