Solidification structures and magnetic properties of NdFeB alloys produced by twin-roller quenching technique

Abstract

Abstrmt -The relationship between microstructures and magnetic properties of NdFeB ribbons or flakes produced by twin-roller quenching was investigated. Dependent on the process parameters magnetically isotropic cell structures or anisotropic columnar structures were obtained. The magnetic properties of the columns did not meet the expections. High press forces on the rollers did not improve the anisotropy of the partially pulverized flakes. The results are discussed in terms of constitutional conditions and deformation mechanisms.

Permanent magnets based on R-Fe-B and R-Fe-C alloys

“…The single-roller and twin-roller techniques have been used to produce anisotropic flakes from the melt , Alehtar et al 1989, Kuji et al 1989, Harada et al 1990b, Zaluska et al 1991, Grünberger et al 1994. In the single-roller technique, the alignment of the c-axis of the tetragonal Nd 2 Fe 14 B phase occurs via directional solidification by the formation of columnar structures.…”

“…The microstructural transition from columnar dendrites to equiaxial grains is attributed to the morphological changes in the solidification of undercooled melts. According to Grünberger et al (1994), the limits of the twin-rolling process control and also the constitutional conditions prevented the solidification of fine columnar structures with good magnetic properties across the whole flakes. High press forces lead to the deformation of the columnar structure without enhancement of the properties.…”