Effect of the dehydrogenation speed and Nd content on the microstructure and magnetic properties of HDDR processed Nd-Fe-B magnets

Abstract

The effect of Nd content and dehydrogenation speed on the microstructure and magnetic properties of hydrogenation-disproportionation-desorption-recombination (HDDR) processed Nd-Fe-B magnetic powders was studied. The NdxB6.4Ga0.3Nb0.2Febal (x=12.5-13.5, at.%) mold casting alloys were subjected to HDDR process after homogenization heat treatment. During desorption-recombination stage, dehydrogenation speed and time were systematically changed to control the speed of the desorption-recombination reaction. The higher Nd content resulted in better magnetic properties of the HDDR powder, and this was attributed to the thicker and more uniform Nd-rich phase at grain boundaries. It was also confirmed that the slow dehydrogenation speed could maximize the effect of high Nd content on the magnetic properties of HDDR powder. At the optimized dehydrogenation speed, the coercivity and remanence was 15.3 kOe and 13.0 kG, respectively, at 12.9 at.% Nd content, which resulted in a (BH)max of 36.8 MGOe.

Effect Of The Desorption-Recombination Temperature On The Microstructure And Magnetic Properties Of HDDR Processed Nd-Fe-B Powders

“…It should be however noted that the remanence of 820 • C-DR treated HDDR powders is higher than that of 810 • C-DR treated HDDR powders in the Nd content range from 12.5 to 13.5 at.%. This result is consistent to our previous result in which slow DR speed suppressed temperature drop during DR stage and resultingly enhanced remanence due to highly textured microstructure [11]. Based upon these results, it can be concluded that higher temperature during DR stage results in higher degree of anisotropy of the HDDR powders.…”