Directional solidification of Co-Cu-R permanent-magnet alloys

Co-Fe-Cu-Ce permanent-magnet alloys have been prepared by directional solidification using a modified Bridgman technique. Samples melted at low superheat temperatures (
\DeltaT \sim 20\deg
C above the melting point of about 1100°C) and solidified at moderate rates (∼2.3 cm/h) resulted in a reasonably homogeneous columnar grain structure with a preferred crystallographic orientation. The
c
axis is generally aligned within 15° of the growth axis. Increasing the speed of solidification led to a fine-grained structure with no texture, while decreasing the speed led to coarse columnar grains with erratic orientation. A large superheat temperature (
\DeltaT \sim 300-400\deg
C resulted in a reaction of the liquid with the alumina crucible wall and led to the formation of face-centered cubic Co-rich dendrites. With the modified Bridgman technique, oriented samples 8 cm long and 2.54 cm in diameter have been prepared with good magnetic properties. After annealing at 1000°C followed by aging at 400°C, a Co
3.5
Fe
0.5
CuCe alloy exhibited values of
i
H
c
= 7000 Oe, B
r
= 6100 G, and
(BH)_{\max} = 9.2
MG.Oe. A Co
3.6
Fe
0.5
Cu
0.9
Ce alloy exhibited values of
i
H
c
= 6000 Oe,
B_{r} = 6250
G, aud
(BH)_{\max} = 9.5
MG.Oe after similar treatment.