Magnetic hysteresis properties of melt-spun Nd-Fe-B alloys prepared by centrifugal method

Magnetic hysteresis properties and microstructure peculiarities of melt spun Nd-Fe-B alloys (ribbons) prepared by melt quenching onto the internal surface of an iron spinning wheel at tangential speeds in the range 5-20 m/s are reported. The alloy composition was Nd-36% wt, B-1.2% wt, and Fe-remainder. It was found that the coercivity of ribbons does not practically depend on the wheel speed in applied range(18 kOe at 5 m/s and 22 kOe at 20 m/s), whereas the grain size of the basic phase (2-14-1) steadily decreases when the speed rises, starting from 2-3 mu m for 5 m/s alloy down to the 200-300 nm for 20 ms alloy. All ribbons have normal convex demagnetization curves, even those prepared at low wheel speeds (without peculiar step near H similar to 0, which usually exists on such curves for traditionally prepared underquenched melt-spun Nd-Fe-B alloys). Grinding the ribbon in a vibration mill causes the coersivity drop to 7 kOe after 120 min of treatment. However, this operation increases the powder alignment ability and, as a result, the energy product for a fully dense magnet from anisotropic powder prepared from some ribbons rises to 20-23 MGOe. (C) 1998 Elsevier Science B.V. All rights reserved.