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
_9.5
Fe
_72.5-y
Ti
_2.5
Zr
_0.5
Cr
_y
B
_{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
_9.5
Fe
_72.5
Ti
_2.5
Zr
_0.5
B
₁₅
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,
_i
H
_c
=8.2 kOe and (BH)
_max
=7.2 MGOe could be attained in Nd
_9.5
Fe
_71.5
Ti
_2.5
Zr
_0.5
Cr
₁
B
_14.5
C
_0.5
. In addition, for R
_9.5
Fe
_71.5
Ti
_2.5
Zr
_0.5
Cr
₁
B
_14.5
C
_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,
_i
H
_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).