MAGNETIC-PROPERTIES AND MICROSTRUCTURE OF MELT-SPUN ND-FE-GA-B ALLOYS

The magnetic and microstructural properties of melt-spun Nd18Fe76-XGaX B6 alloys have been studied as a function of Ga content. Coercivities of 17 kOe were obtained in underquenched samples having a large grain size of 500 nm. Samples prepared at wheel speeds of 15-19 m/sec, as we ll as overquenched (40 m/sec) and subsequently annealed, gave coercivi ties of around 20 kOe with no significant improvement of H-c upon Ga s ubstitution. In Ga-free samples prepared by annealing highly overquenc hed ribbons (at 60 m/sec) only moderate coercive fields could be achie ved (14 kOe). These samples had grain sizes of 70-100 nm. However Ga s ubstituted samples prepared under the same conditions have a fine grai n structure consisting of unequiaxed grains with size around 20 nm and show coercivities up to 23 kOe.