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 ( 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 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 ( 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 Co3.5Fe0.5CuCe alloy exhibited values ofiHc= 7000 Oe, Br= 6100 G, and MG.Oe. A Co3.6Fe0.5Cu0.9Ce alloy exhibited values ofiHc= 6000 Oe, G, aud MG.Oe after similar treatment.