Abstract
For the HDDR Nd 13.5Fe 79.5B 7 magnetic powders, effects of disproportionation time and hydrogen pressure on the anisotropy were studied during the slow desorption stage. Studies showed that shorter disproportionation times caused the magnetic powders displaying higher anisotropy. With increasing disproportionation times, the degree of crystallographic alignment decreased. This in turn caused a drop in remanence and anisotropic character. Longer disporportionation times have also been correlated to a change in disproportionated microstructure from lamella to columnar. XRD (X-Ray Diffraction) studies showed that except NdH 2,α–Fe and Fe 2B, no other phases were included in the disproportionation mixture. This elucidated that the strong anisotropy is only related to a lamella disproportionation microstructure, which corresponds to a short disproportionation times. The lamella disproportionation microstructure may remain or inherit the alignment of original Nd 2Fe 14B grain, and may also be related to the alignment of the newly formed Nd 2Fe 14B grain. Thus, the anisotropic formation mechanism of ternary magnetic powders accords with “anisotropy-mediating phase” model. If the disproportionation mixture were carried out an optimum hydrogen pressure treatment during the HDDR process, the degree of crystallographic alignment can be further enhanced.
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