Strategy of refining the microstructure of Nd-Fe-Co-Ga-B ribbons by high-speed melt-spinning and annealing

Abstract

• Increasing the melt-spinning speed to 50 m/s refines the grain size. • Changing the crystallization process is the mechanism of grain refinement. • The size of equiaxed grains in the annealed ribbons is reduced to 50–200 nm. • The intense exchange coupling effect contributes to the higher remanence. • The microstructure evolution models are proposed. Given the uneven grain size distribution in the ribbons melt-spun at 25 m/s, the strategy of improving the microstructure and magnetic properties of the ribbons by increasing the melt-spinning speed is discussed. The experimental results show that the grain size of Nd 13.65 Fe 73.55 B 5.6 Co 6.6 Ga 0.6 ribbons annealed at 700 °C is reduced to 50–200 nm by melt-spinning at 50 m/s. The change in the crystallization process is the primary mechanism for grain refinement. At high quenching speed, the amorphous matrix is formed first in the as-spun ribbons, and then uniform crystallization can be achieved through annealing. Compared to the annealed ribbons melt-spun at 25 m/s, the Mr and M 2T increased by ∼8 % due to the intense exchange coupling effect and the refined grains.