A Study on the Phase Evolution and Magnetic Properties of Nd $_{9.5 - 1.5{\rm x}}$Fe$_{{\rm bal}.}$Ti$_{2.5}$ Zr$_{0.5}$ B$_{15 + 2{\rm x}}$ $({\rm x}=0 \hbox{--}4)$ Bulk Magnets

Phase evolution, microstructure, and magnetic properties of Nd
_9.5-1.5x
Fe
_bal.
Ti
_2.5
Zr
_0.5
B
_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 Fe
₃
B (o-Fe
₃
B) 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-Fe
₃
B) in the as-cast state, consequently, exhibit extremely low permanent magnetic properties.