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http://dx.doi.org/10.4283/JKMS.2015.25.4.111

Improving Reproducibility of Coercivity of HDDR-treated Nd-Fe-B-type Material by Controlling Hydrogen Decrepitation  

Kim, Kyung Min (Pukyong National University)
Kim, Ja Young (Pukyong National University)
Kwon, Hae-Woong (Pukyong National University)
Lee, Jeong Gu (Korea Institute of Materials Science)
Yu, Ji Hun (Korea Institute of Materials Science)
Publication Information
Journal of the Korean Magnetics Society / v.25, no.4, 2015 , pp. 111-116 More about this Journal
Abstract
Practical difficulty in the HDDR (hydrogenation - disproportionation - desorption - recombination) processing of Nd-Fe-B-type alloy is a poor reproducibility of coercivity of the HDDR-treated material. In an attempt to improve the reproducibility of coercivity of the HDDR-treated $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ alloy, the hydrogen decrepitation was carefully controlled so as to induce more extensive micro-cracks in the particle. Prior to the hydrogenation and disproportionation reaction of HDDR processing, an additional hydrogen degassing was carried out at an elevated temperature of $600^{\circ}C$ under vacuum for the previously hydrogen decrepitated particle. During the additional hydrogen degassing the lattice of hydrogen absorbed $Nd_2Fe_{14}B$ phase was further shrunken, hence more microcracks were introduced in the particle due to its brittle nature. Particles with more micro-cracks had more homogeneous hydrogen absorption and desorption reaction during the HDDR-treatment. The improved reproducibility of coercivity of the HDDR-treated material was attributed to the improved homogeneity of the HDDR reactions due to the presence of more micro-cracks.
Keywords
Nd-Fe-B; HDDR; hydrogen decrepitation; micro-crack; coercivity;
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