Journal of Magnetics

The Korean Magnetics Society (한국자기학회)
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Coercivity of Hot-pressed Compacts of Nd-Fe-B-type HDDR-treated Powder

  • Abdul Matin, Md. (Department of Materials Science and Engineering, Pukyong National University) ;
  • Kwon, Hae-Woong (Department of Materials Science and Engineering, Pukyong National University) ;
  • Lee, Jung-Goo (Korea Institute of Materials Science (KIMS)) ;
  • Yu, Ji-Hun (Korea Institute of Materials Science (KIMS))
  • Received : 2014.02.14
  • Accepted : 2014.04.02
  • Published : 2014.06.30
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Abstract

$Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ HDDR-treated powder was compacted by hot-pressing using different configurations of dies and heating rates. The die configurations were especially different in terms of the evacuation system that was used in heating for hot-pressing. The coercivity in the compacts was influenced by the evacuation system of the die and heating rate. In spite of the identical hot-pressing temperature and heating rate, coercivity was radically reduced above $600^{\circ}C$ in the compacts prepared in the closed-type die compared to that in the compacts prepared in the open-type die. The coercivity in the compacts prepared in the closed-type die decreased with increasing heating rate and the value further increased when extreme high heating rate was employed. $Nd_{12.5}Fe_{80.6}B_{6.4}Ga_{0.3}Nb_{0.2}$ HDDR-treated powder contained a significant amount of residual hydrogen (approx. 1500 ppm) in the form of $Nd_2Fe_{14}BH_x$ hydride. The dramatic coercivity decrease in the compact prepared in the closed die is attributed to the disproportionation of $Nd_2Fe_{14}BH_x$ hydride. High coercivity is mainly due to the effective desorption of hydrogen or the suppression of hydrogen-related disproportionation upon hot-pressing.

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References

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