A Study on the Phase Evolution and Magnetic Properties of Nd9.5-1.5xFebal.Ti2.5Zr0.5B15+2x (x=0-4) Bulk Magnets

Phase evolution, microstructure, and magnetic properties of Nd9.5-1.5xFebal.Ti2.5Zr0.5B15+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 Fe-3 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 Fe-3 B 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 Fe-3 B(o-Fe3B) in the as-cast state, consequently, exhibit extremely low permanent magnetic properties.