• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.432-436
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• 1995

The hydrogen decrepitation behaviour of the $Sm_{2}Fe_{17} alloy containing 4at%Nb was examined by means of DTA and SEM metallography, and the magnetic properties of the alloy were studied by means of VSM or TMA. It has been found that a simple hydrogenation and degassing treatment for the alloy caused a poor hydrogen decrepitation. The cycle treatment consisting of repeated hydrogenation and degassing, however, caused a severe hydrogen decrepitation with a combination of intergranular and transgranular failure. The disproportionation temperature of the hydrogenated $Sm_{2}Fe_{17}-type alloy was enhanced significantly by small addition of Nb. It has also been found that the Curie temperature of $Sm_{2}Fe_{17} matrix phase in the Nb-containing alloy has been enhanced by the hydrogenation, and this was attributed to the increase in interatomic distance between the neighbouring iron atoms caused by the interstitial occupancy of the hydrogen atom into the $Sm_{2}Fe_{17}-type lattice. The magnetisation of the $Sm_{2}Fe_{17} alloy containing Nbwas found to be lower than that of the Nb-free alloy, and this was explained by the dilution effect due to the presence of the paramagnetic $Sm_{2}Fe_{17} phase.

• Journal of Magnetics
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• v.4 no.2
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• pp.55-59
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• 1999

In an attempt to find an effective production way of the$ Sm_2Fe_{17}N_{x-}type material, the Sm_2Fe_{17-}$type alloy with chemical composition of Sm 22.7 wt.%, Fe72.3 wt.% Nb 5.0wt.% was subjected to a HD (hydrogen decrepitation) treatment prior to a nitrogenation, and its effect on the formation of the nitride material was investigated. The nitrogenation behaviours of the alloy were investigated using a TPA(thermopiezic analysis), TMA, and DTA under nitrogen gas, and XRD. It has been found that the previous HD treatment significantly facilitated the formation of $Sm_2Fe_{17}N_{x-}$type nitride, and this was accounted for by the clean surface and the finer particle size of the powder caused by the HD treatment. It has also been found that the hydrogen atoms existing in the initial HD-treated alloy were removed almost completely during the nitrogenation. The heat output associated with the nitrogenation of the previously HD-treated alloy was found to be significantly smaller than that of the as-cast alloy.

• Journal of the Korean Magnetics Society
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• v.25 no.4
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• pp.111-116
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• 2015

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.

• Proceedings of the Korean Magnestics Society Conference
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• 1999.04a
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• pp.70-71
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• 1999

• Journal of Powder Materials
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• v.17 no.5
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• pp.359-364
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• 2010

In an attempt to optimize the magnetic properties of (Nd, Dy)-Fe-B sintered magnets, hydrogenation and post-sintering heat treatment processes were investigated at various hydrogenation temperatures and heat treatment temperatures. The coercivity of (Nd, Dy)-Fe-B sintered magnets hydrogenated at $400^{\circ}C$ increased to about 1.2 kOe without any detrimental effect on the remanence. Moreover, the coercivity of the magnets was enhanced further by a consecutive $2^{nd}$ and $3^{rd}$ step heat treatment. These results eventually leaded to the reduction of the Dy content in a high coercive (> 30 kOe) (Nd, Dy)-Fe-B sintered magnets, as much as 10%.