HYDROGEN ABSORPTION AND DISPROPORTIONATION OF MELT-SPUN ND-FE-B RIBBONS

Hydrogen absorption and disproportionation of melt-spun Nd-Fe-B-based ribbons are significantly affected by quench state (wheel speed). The initial hydrogen absorption temperature corresponding to the formation of the Nd2Fe14BHx-type phase shifts from -120-degrees-C for ingot to 250-300-degrees-C for ribbons spun at 13, 15, 17, 20, 22, and 24 m/s w heel speeds. This shift is presumably related to the fact that ribbons are considerably more inert than ingot, which is typical of Nd-Fe-B m aterials. The hydrogen disproportionation temperature, however, monoto nically decreases with increasing wheel speed from > 700-degrees-C for ingot to 530-degrees-C for 24 m/s ribbons. Hydrogen absorption due to disproportionation exhibits a two-step feature for wheel speeds great er-than-or-equal-to 20 m/s. The onset and size of the lower temperatur e step correlates with the presence and amount of an amorphouslike com ponent in the x-ray diffraction spectra of as-spun ribbons. The amorph ouslike component is detectable only for wheel speeds greater-than-or- equal-to 20 m/s, and both the amount of amorphouslike component and th e size of the lower temperature step in the hydrogen absorption increa se with increasing wheel speed.