Effect of Annealing Treatment on Magnetic Properties of Melt-Spun Nd-Fe-Co-B-V Ribbons

Amorphous ribbons of Nd11Fe72Co8B7.5V1.5 alloy were prepared by the single-roller rapid-quenching method at a substrate surface velocity of 20.7 m/s, and the effect of annealing on the magnetic properties was studied. The optimum annealing conditions were 650°C for 5 min.; crystallized ribbon thus annealed had a (BH)max of 148.6 kJ/m³. TEM observations indicated that the fine grains of ribbons crystallized from the amorphous state were from 25 to 33 nm in diameter. The temperature coefficients (in the range 25 to 125°C) of Br and HcJ for ribbon crystallized from amorphous Nd11Fe72Co8B7.5V1.5 alloy were ¿0.083%/°C (reversible) and ¿0.375%/°C (irreversible), respectively. The maximum energy product obtained for a Nd11Fe72Co8B7.5V1.5 bonded magnet prepared from ribbons annealed at 650°C was 94.2 kJ/m³; under these conditions the bonded magnet had a density of 6.25 Mg/m³.