MAGNETIC HYSTERESIS PROPERTIES OF MELT-SPUN ND-FE-B ALLOYS PREPARED BY CENTRIFUGAL METHOD

Magnetic hysteresis properties and microstructure peculiarities of mel t spun Nd-Fe-B alloys (ribbons) prepared by melt quenching onto the in ternal surface of an iron spinning wheel at tangential speeds in the r ange 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 do es not practically depend on the wheel speed in applied range(18 kOe a t 5 m/s and 22 kOe at 20 m/s), whereas the grain size of the basic pha se (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 ribb ons have normal convex demagnetization curves, even those prepared at low wheel speeds (without peculiar step near H similar to 0, which usu ally exists on such curves for traditionally prepared underquenched me lt-spun Nd-Fe-B alloys). Grinding the ribbon in a vibration mill cause s the coersivity drop to 7 kOe after 120 min of treatment. However, th is operation increases the powder alignment ability and, as a result, the energy product for a fully dense magnet from anisotropic powder pr epared from some ribbons rises to 20-23 MGOe. (C) 1998 Elsevier Scienc e B.V. All rights reserved.